Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Mon Aug 14 2023

.SYNOPSIS...The local weather conditions will begin to dry out
today, and despite some shallow patches of moisture streaming
across the region, expect limited shower activity during the next
few days. A dense Saharan Dust Layer accompanying this drier air
mass will maintain hazy skies, with the highest concentrations
expected on Tuesday and Wednesday. While excessive rainfall risk
levels will decline during the next few days, excessive heat
hazard risks will pose a higher threat, with areas observing heat
index values exceeding 111 degrees. Moisture steered by a wind
surge and a subsequent tropical wave may enhance wetting rains by
the end of the work week, but conditions will likely dry out
during the weekend. Increasing winds will maintain choppy
conditions, with deteriorating hazardous seas likely by the end of
the week.


&&

.SHORT TERM...Today through Wednesday...

Overnight, some brief trade wind showers moved across eastern Puerto
Rico and the U.S. Virgin Islands. However, dry air with particles of
Saharan Dust moved over the islands by late night, lowering the
chances for rainfall activity. Winds were generally out of the east,
around 5 and 10 mph. Low temperatures fell to around the upper 70s
to lower 80s across lower areas. While at higher elevations, they
range around the 70s.

Today, expect the Saharan Air Layer to continue to move in, as well
as some moisture at times, resulting in isolated to scattered
showers with hazy skies and reduced visibility. The latest
precipitable water models suggest around normal PW content across
the area. However, dust aerosol guidances now show optical depths
around 0.20 and 0.30 throughout the day. For that reason, no
significant rainfall is anticipated. During the day, the low and
urban areas of the islands are foreseen to experience heat indices
around 102 degrees Fahrenheit and higher. The southern, eastern
interior, and eastern sections of Puerto Rico will experience heat
indices greater than 108 degrees Fahrenheit, and for that reason, a
Heat Advisory was issued. However, the northern and western areas of
Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands are
forecast to experience heat indices above 113 degrees. Therefore an
Excessive Heat Warning was issued for those areas. With these
conditions, heat exhaustion and heat strokes are possible, and we
urge people to follow the necessary precautions to avoid any of
those mentioned above. Although breezy conditions will continue due
to the robust high-pressure system that remains anchored over the
northern Atlantic, expect the movement of showers at times assisted
by the high-pressure system. The afternoon convection across western
Puerto Rico and the San Juan metro area could produce limited water
ponding across urban areas.

On Tuesday, expect an increase in Saharan Dust concentrations and a
significant decrease in visibilities. Below-normal precipitable
water values will prevail through mid-week. However, afternoon
convection across the western sections of Puerto Rico cannot be
ruled out. At this time, hot weather conditions are foreseen across
the islands. Therefore, heat advisories and warnings could be issued
during the period.

By mid-week, expect hot and hazy weather conditions to prevail again
across Puerto Rico and the U.S. Virgin Islands.

.LONG TERM...Thursday through Monday...

Based on the most recent model guidance, a transition from a dry
to a wet weather pattern is likely between Thursday and Friday,
followed by drying again during the weekend into early the
following week. On Thursday, a persistent drier air mass
accompanied by a dense Saharan Air Layer, with aerosol optical
depth (AOD) values of 0.20-0.30, will gradually be replaced by a
moist air mass. Despite variations in AOD values, particularly
during the wettest periods, conditions will remain hazy through
the end of the period. Increased moisture levels, generated by a
wind surge and subsequent tropical wave, should enhance showers
with thunderstorm activity and an increased excessive rainfall
risk between Thursday night and Friday night. This wet period will
be short-lived, replaced by yet another drier air mass invading
the northeastern Caribbean region from the east from Saturday
onwards. Total Precipitable Water (PWAT) values will range from
around 1.8 inches on Thursday morning to approximately 2.4 inches
by Friday afternoon, followed by a gradual drop in PWAT, falling
as low as 1.4 inches by Monday. Despite these variations,
afternoon showers with isolated thunderstorm development are
likely each day, even during dry periods, as shallow moisture
patches stream across the region steered by generally easterly
winds. Wind and excessive heat hazard risks will prevail through
the long-term forecast period, with the highest impacts across
coastal areas and lower elevations, where wind speeds and heat
index values can reach the 15-25 mph and 108-111 degrees range,
respectively.


&&

.AVIATION...VFR at all terminals. HZ will prevail across all
terminals after 14/12Z. At 14/17Z TJBQ will experience brief MVFR
conditions due to Isold VCTS and HZ. SFC Wnd fm E 15-20 kts with hir
gusts btw 24-28 kts especially near/with TS. Winds will decrease to
less than 14 kts after 13/22Z.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated steady seas between 2
and 5 feet. Deteriorating marine conditions are likely today, and
small craft should exercise caution due to seas up to 6 feet
and/or winds up to 20 knots, mainly across the Atlantic and
Caribbean waters of Puerto Rico, Mona Passage, and Anegada
Passage. Seas should remain at 5 feet or below with winds up to 15
knots elsewhere across the local waters. Increasing winds may
yield hazardous marine conditions for small craft by the end of
the workweek. There is a moderate rip current risk beaches of
northern, eastern, southeastern, and southwestern Puerto Rico,
Vieques, Culebra, and the U.S. Virgin Islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Tue Aug 15 2023

.SYNOPSIS...A drier air mass and dense Saharan Dust Layer will
maintain stable conditions and hazy skies, with the highest dust
concentrations today and Wednesday. This moderate to severe dust
event can be harmful, aggravating any respiratory conditions. to
Excessive heat hazard risks will pose a higher threat during the
next few days, with areas observing heat index values exceeding
111 degrees. Moisture steered by a wind surge and a subsequent
tropical wave may enhance wetting rains by the end of the work
week. Increasing winds will maintain choppy conditions, with
deteriorating hazardous seas likely by the end of the workweek.


&&

.SHORT TERM...Today through Thursday...

Overnight, passing showers moved across northern Puerto Rico,
Culebra, and the U.S. Virgin Islands. Mainly hazy skies prevailed as
more dry air with Saharan Dust particles filtered over the islands
at night. The wind flow was generally around 5 and 10 mph from the
east-northeast. Low temperatures remain in the low to mid-80s across
coastal areas. While at higher elevations, they stay in the mid to
upper 70s.

Today, expect higher concentrations of Saharan Dust particles to
move in and decrease the visibility significantly. Dust aerosol
guidances now show optical depths around 0.30 and 0.70 throughout
the day. For that reason, no significant rainfall is anticipated.
Despite the dry air across the area, brief passing showers over
northern and eastern Puerto Rico and the local islands cannot be
ruled out due to a robust high-pressure system that continues to
enhance breezy conditions from the east-northeast. Therefore, if the
afternoon convection develops, the highest rainfall accumulations
will be seen across the western-southwestern sections of Puerto
Rico. During the day, the northern, western, eastern, and eastern
interior sections of Puerto Rico will experience heat indices above
112 degrees, and for that reason, an Excessive Heat Warning was
issued. A Heat Advisory was issued for the southern areas of P.R.,
Vieques, Culebra, and the U.S. Virgin Islands due to heat indices
above 108 degrees. With these conditions, heat exhaustion and heat
strokes are possible, and we urge people to follow the necessary
precautions to avoid any of those mentioned above. By mid-week,
expect the below-normal precipitable water values to prevail.
Therefore, expect hot, dry, and hazy weather across Puerto Rico and
the U.S. Virgin Islands. We foresee that these hazy conditions could
make many people uncomfortable due to poor air quality, and we urge
people with respiratory illness to follow the necessary precautions
established by health professionals.

On Thursday, expect the dry air with Saharan Dust particles to
continue across the forecast area, but in lower concentrations, as
it keeps moving out of the region and a moisture surge moves in
across the islands. At this time, Thursday looks like the transition
day from a dry to a wet weather pattern.

.LONG TERM...Friday through Tuesday...

Based on the most recent model guidance, a delay in the transition
from a wet to a dry weather pattern has been introduced, now
likely from Sunday onwards. Increased moisture levels, generated
by a wind surge and weak tropical wave, should enhance showers
with thunderstorm activity and an increased excessive rainfall
risk for an extended period, now through Sunday. Weather
conditions will begin to dry out on Sunday, with a patchy weather
scenario likely through the rest of the forecast period. Total
Precipitable Water (PWAT) values will range from around 2.2 inches
on Friday, followed by a brief drop in PWAT on Saturday to about
1.7 inches, then rising to approximately 2 inches on Sunday and
back to 1.4-1.6 inches between Monday and Tuesday. Despite these
variations, afternoon showers with isolated thunderstorm
development are likely each day, even during dry periods, as
shallow moisture patches stream across the region steered by
generally easterly winds. Wind and excessive heat hazard risks
will prevail through the long-term forecast period, with the
highest impacts across coastal areas and lower elevations, where
wind speeds and heat index values can reach the 15-25 mph and
108-111 degrees range, respectively.


&&

.AVIATION...Again, VFR conds will continue to prevail at all TAF
sites with reduced visibilities during the forecast cycle.
Visibilities should remain 6SM. Easterly winds 15 to 20 knots with
higher gusts at/after 15/14Z. Winds will decrease to less than 16
kts after 15/23Z.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated steady seas between 2
and 5 feet. Wind-driven choppy marine conditions are likely today,
and small craft should exercise caution across most local waters.
Increasing winds may yield hazardous marine conditions for small
craft by the end of the workweek. There is a moderate rip current
risk for most north-, east-, and southeast-facing beaches of
Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Wed Aug 16 2023

...New SYNOPSIS, AVIATION, MARINE...

.SYNOPSIS...The extensive Saharan Air Layer (SAL) will peak this
morning into the early afternoon, thus maintaining hazy conditions
with limited shower activity. The variable cloud cover and dense
suspended dust particulates during the overnight and early morning
hours, maintained minimum temperatures warmer than normal due to limited
radiative cooling. This warm spell and overall dry atmospheric conditions
will continue across most coastal and urban areas in Puerto Rico and
the U.S. Virgin Islands. Consequently, Excessive Heat Warnings and
Heat Advisories were required today for several areas between 10 am
and 5 pm AST. Breezy northeasterly winds will persist especially along
the coastal areas, then becoming more easterly Thursday into Friday.
Another easterly wind surge is forecast by Saturday. Moisture advection
will be limited across the region, however passing clouds and few tradewind
showers can be expected, especially across the coastal waters and windward
sections in the morning followed by limited afternoon shower development
mainly in west and southwest Puerto Rico.

&&

.SHORT TERM...Today through Friday...
Once again, passing showers over northern and eastern Puerto Rico,
as well as St. Croix overnight. Mainly hazy skies prevailed as a
denser dry air mass with Saharan Dust particles moved over the U.S.
Virgin Islands, Puerto Rico, Vieques, and Culebra. The wind flow was
generally around 5 and 10 mph from the east-northeast. Overnight low
temperatures remain in the low to mid-80s across coastal areas.
While at higher elevations, they stay in the mid to upper 70s. These
warmer low temperatures experienced at night were associated with
the dense haziness that did not allow most of the energy irradiated
by the sun during the day to be released.

Saharan Dust particles will continue to filter across the forecast
area today, decreasing visibility significantly. Dust aerosol
guidances now show optical depths around 0.40 and higher throughout
the day. As mentioned in previous discussions, this can exacerbate
respiratory conditions in immunocompromised, vulnerable, and
sensitive groups. The latest model guidance suggests prevailing
below-normal climatological levels of precipitable water across the
islands today. Any rainfall activity that does develop across the
islands should be minimal/not significant due to the dry air mass
and breezy conditions. The robust high-pressure system over the
Atlantic will continue to enhance east-northeasterly winds and
breezy conditions. This wind flow will push the afternoon rainfall
activity across the western-southwestern quadrant of P.R. Today,
expect daily maximum temperatures to range in the upper 80s to 90s
along the coastal areas, while maximum temperatures should remain in
the upper 70s to 80s along the higher elevations. Therefore, expect
another day with warm temperatures across the tropical islands.
During the day, we anticipate heat indices above 112 degrees
Fahrenheit along the north-central to northwestern, western,
southwestern, and south-central sections of Puerto Rico, as well as
Vieques, Culebra, and the U.S. Virgin Islands. Therefore, an
Excessive Heat Warning was issued for those areas. The expected heat
indices above 108 degrees prompted the issuance of a Heat Advisory
for northwestern, eastern, and southwestern Puerto Rico through 5 PM
AST today.

On Thursday, expect a gradual increase in precipitable water content
as a wind surge approaches the region. Most available moisture will
remain below 700 mb, with drier air aloft. Nonetheless, expect the
Saharan Dust concentrations to remain across the forecast area. At
this time, Thursday looks like the transition day from a dry to a
wet weather pattern.

By the end of the workweek, expect an increase in moisture generated
by a wind surge and a weak tropical wave. These weather features
should enhance showers and thunderstorm activity.

Overall, the Saharan Air Layer (SAL) will continue to affect Puerto
Rico and the U.S. Virgin Islands through the short-term forecast
period. Therefore, dry, hazy, and hot conditions should prevail on
Wednesday, with Thursday being the transition day from a dry to a
wet pattern on Friday.

&&


.LONG TERM...Saturday through Wednesday...
On Saturday into Sunday, fragments of moisture trailing a weak
tropical wave and the moderate east northeast trades will bring
morning showers to the coastal waters and windward side of the
islands from time to time. The activity will be of short duration
with no significant accumulation forecast at this time. lingering
moisture and good daytime heating will favor some enhanced showers
and isolated thunderstorms on Saturday and Sunday. Based on
recent model guidance, a drier airmass will gradually spread
across the region along with low level moisture erosion as the
mid to upper level ridge will build across the region and a strong
surface high pressure ridge will reestablish across the west and
central Atlantic. From late Sunday and during the rest of the
forecast period, weather conditions will continue into a drying
trend, with only periods of a patchy shallow passing low level
clouds and limited trade wind showers likely. The suggested
layered Precipitable Water values (PWAT) will range between 1.7
and 1.95 inches Saturday into early Sunday, then a rapid drying
trend is expected thereafter with values between 1.40-1.60 inches
by late Sunday into Monday and through Wednesday. Surface winds
and steering flow is forecast to become more east northeast by
that time. Regardless of the overall dry pattern expected, early
morning passing showers and isolated to scattered afternoon convection
will remain likely each day, as pockets of shallow moisture will
continue to stream across the region steered by the moderate to
locally strong easterly winds, and combined with good daytime
heating. Overall breezy conditions and excessive heat hazard risks
conditions are so far expected to persist through the long-term
forecast period, with the main impacts focused along the coastal
and urban areas. Significant urban and small stream flooding is
not anticipated during the periods but isolated areas of ponding
water on roads and in poor drainage areas cannot be ruled out
especially during the afternoon hours in western Puerto Rico.

&&

.AVIATION...VFR conds will continue to prevail at all TAF sites
with reduced visibilities during the forecast cycle. Visibilities
should remain 6SM due to HZ. Easterly winds 15 to 20 knots with
higher gusts at/after 16/14Z. Winds will decrease to less than 16
kts after 15/23Z.

&&

.MARINE...
Mariners can expect choppy wind driven seas between 3 and 5 feet,
with occasional seas up to 6 feet and winds between 15 and 20 knots
and occasionally higher gusts across most local waters today and
increasing to near advisory criteria for portions of the offshore
waters by Thursday.

Beachgoers, the risk of rip currents is moderate for most beaches
in Puerto Rico and the U.S. Virgin Islands.

[cycloneye]

517 AM AST Thu Aug 17 2023///...

.SYNOPSIS...
Expect an increase of rain today due to a tropical wave that is
passing by. Heavier rain today may lead to minor flooding,
especially across western Puerto Rico. Windy conditions will
continue throughout the next few days, meanwhile Saharan Dust
continues to linger until at least Friday. The risk of rip
currents is moderate for most beaches today.

&&

.SHORT TERM...Today through Saturday...
A tropical wave with axis now crossing Puerto Rico and the Mona passage
this morning, will continue to bring additional showers and isolated
thunderstorms over the regional waters and parts of the islands. Sufficient
moisture availability along with good daytime heating will favor afternoon
shower and isolated thunderstorm development. The associated heavy rains
is will lead to ponding of water on roads and in poor drainage areas,
with minor urban and small stream flooding possible in isolated areas
especially during the afternoon, over the west sections of Puerto Rico.
Winds will increase today through Friday as a high pressure ridge will
reestablish north of the region resulting in the breezy easterly winds,
then becoming more northeasterly by Friday and Saturday.

The Saharan Air Layer(SAL) with a moderate to high concentration of
of suspended dust particulates will continue to be mixed in with the
moisture accompanying the tropical wave. It is however expected to gradually
diminish throughout the day at least until Friday. Hazy and muggy conditions
will therefore continue across the region. Another surge of dense Saharan
dust is also expected by Saturday and this will also aid in maintaining
the hot and hazy weather pattern. The high humidities and near normal
or slightly above normal temperatures will bring maximum heat indices
along almost all coastal and urban areas to limited to elevated Heat
Advisories conditions by late morning and through the afternoon hours.
As mentioned, during the afternoon hours, good daytime heating and
local effects combined with the brisk E-NE steering winds,will favor
shower and thunderstorm activity to develop particularly over parts
of the interior and west sections of Puerto Rico; including around
the San Juan metro and mainly downwind of the USVI during the afternoon
hours.

On Friday and Saturday expect the moderate to strong east to northeast
winds to continue to steer passing showers across the coastal waters
and the windward side of the islands, with some showers bringing periods
of heavy rains at times during the overnight and early morning hours
especially over the USVI and eastern PR. This will be followed by afternoon
convection with isolated but enhanced showers and thunderstorm activity
particularly over the interior and west sections of Puerto Rico, and
lesser activity in and around the USVI on Friday and Saturday. So far,
Saturday being the driest day, but with continued hazy conditions. Slightly
above normal high temperatures and maximum heat indices are forecast
to continue during the short term period, especially for urban, coastal
and areas in low elevations, and without relief from periods of isolated
to scattered showers activity and the chance of isolated but strong
thunderstorms activity each day over W interior PR due to intense
heating and local effects.

&&

.LONG TERM...Sunday through Friday...

The combination of a tropical wave passing across the eastern
Caribbean Sea and a Tropical Upper Tropospheric Trough (TUTT) to the
northeast will cause rainy weather on Sunday. Breezy conditions will
allow passing showers to move across eastern Puerto Rico and the
USVI throughout the morning hours followed by afternoon convection
that may bring impressive showers across western Puerto Rico. High
precipitable water values linger across the southern half of the
region on Monday, allowing similar conditions to prevail.

Tuesday through Thursday the TUTT leaves the local area and
moisture values go down. This will promote a seasonal pattern of
patchy rainfall across the eastern half of the region followed by
stronger afternoon activity due to diurnal heating, seabreeze
effects, and orographic lifting. This whole week is expected to be
hot as well, especially for urban coastal areas. On Friday, the
GFS suggests that a tropical system will be passing north of
Anguilla. Uncertainty remains about how this system will evolve
and the effects it will have on the local islands, therefore
continue to monitor updates from the National Hurricane Center
throughout the week.

&&

.AVIATION...Periods of MVFR or even IFR conds will remain possible
at JSJ/JBQ in SHRA/TSRA through at least 17/22z. Elsewhere,
mainly VFR conds to continue with VCSH/-RA likely. Easterly winds
at 15 to 20 knots with higher wind gusts, becoming at 12 knots or
less overnight.

&&

.MARINE...Choppy to hazardous seas to continue through at least
Friday with seas 6 to 8 feet and gusts near 30 knots. In
addition, periods of showers and thunderstorms with strong gusty
winds and frequent lightning are expected across the regional
waters through at least early the upcoming weekend.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
455 AM AST Thu Aug 24 2023

...New SYNOPSIS, AVIATION, MARINE...

.SYNOPSIS...
Issued at 407 AM AST Thu Aug 24 2023

Tropical Storm Franklin is north of the Dominican Republic and
moving north at about 13 mph. Rain bands in the local area have
dissipated and moisture is now near a minimum. The southern
rainband of Franklin is expected to edge back into the area as
Franklin intensifies Friday and Saturday, but when it returns to
the north, southerly flow will bring still warmer temperatures
to the northern portions of Puerto Rico and the U.S. Virgin
Islands. A return to easterly flow on Tuesday will signal a return
to more typical weather for mid August although temperatures will
continue to run just a little above normal.

&&

.SHORT TERM...Today through Saturday...

Calm overnight hours were experienced across the islands, since
external bands of Franklin dissipated over the Mona Passage--only
brushing the western coastline, before 10 PM. Minimum
temperatures were around the upper 60s and lower 70s across
higher elevations of Puerto Rico and around the upper 70s and low
80s across lower elevations of the islands.

Tropical Storm Franklin, was located over the southwestern
Atlantic, 55 miles east northeast of Grand Turk Island at 5 AM
AST, and will continue to influence the wind pattern across the
region into the weekend. Light to moderate southeasterly wind flow
will gradually veer during the next few days, becoming southerly
to south- southwesterly. Through Friday, a mid to upper-level high
pressure system will also be over the area, promoting subsidence
and drier air aloft, and decreasing shower activity. This feature
will erode as a mid to upper-level trough approaches the islands
late Friday into Saturday. A decrease in 850-700 mb moisture is
forecasted through most of Friday, before increasing again late
Friday into Saturday with current model guidance showing tail end
bands of Franklin reaching the region. Saturday is expected to be
the wettest day of the short term forecast period. According to
the current forecast track by the National Hurricane Center (NHC),
Franklin should be well north of the region by this time.

Slightly above normal temperatures and high heat indices are
expected today, particularly across coastal, urban and low elevation
areas. A Heat Advisory is in effect for several municipalities from
10 AM to 5 PM AST. Please refer to the latest NPWSJU and NPWSPN for
more information. Expect possible brief passing showers across
windward sectors of the islands during the morning and overnight
hours. Depending on sky clearing, afternoon convection can ramp up
due to diurnal and local effect, promoting showers and possible
isolated thunderstorms across sectors of interior to
northern/northwestern Puerto Rico.

&&

.LONG TERM...Sunday through Wednesday...

The last remnants of a persistent rainband from Tropical Storm
Franklin will begin receding to the north over the local Atlantic
waters Sunday and drier air will enter the area through Monday.
By Tuesday, Franklin is forecast to be a hurricane more than a
thousand miles north of Mona Island and flow in the lower levels
will turn to the east. Some moisture will return on this flow and
allow us to return to more typical weather for mid-August. This
will mean overnight and morning showers on the east coast of
Puerto Rico, and showers and thunderstorms over the western
interior during the afternoons. Only random showers are expected
in the U.S. Virgin Islands during the long term period, although
downstream showers may form each day.

At upper levels, high pressure over the local area on Sunday will
move north allowing easterly flow to prevail. A weak low will
form in the tropical Atlantic in a westward moving trough on
Monday and pass north of the U.S. Virgin Islands on Wednesday.
Owing to high pressure underneath it and to the north at lower
levels with limited instability, little enhancement is
anticipated to be seen in shower activity.

&&

.AVIATION...
(06Z TAFS)
Issued at 407 AM AST Thu Aug 24 2023

Mainly VFR conditions across all terminals. Afternoon
SHRA/TSRA development could result in brief MVFR conditions at TJBQ
and TJSJ between 24/17-22Z. Generally SE surface windflow at 8-15
kts with seabreeze variations and higher gusts, before decreasing
after 24/22Z. Higher gusts possible near TSRA/SHRA.

&&

.MARINE...
Issued at 407 AM AST Thu Aug 24 2023

Winds and seas will generally remain benign through the period,
although Tropical Storm Franklin will move into the waters north
of Puerto Rico Friday and Saturday. This will bring seas up to
around 5 feet in the Atlantic waters at that time. A rainband from
T.S. Franklin will also bring showers and thunderstorms to the
local Atlantic waters Friday and Saturday which will cause gusty
winds and frequent lightning around the band. Current conditions
at the local buoys show seas of 1.5 to 2.5 feet.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for PRZ001-002-010-012-013.

VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION...MRR
LONG TERM/PUBLIC....WS

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
503 AM AST Sat Aug 26 2023

.SYNOPSIS...

The tail from tropical storm Franklin, now located north of the
region at about 300 miles of San Juan, resulted in a very active
night with strong showers and scattered thunderstorms across the
south coast of Puerto Rico and local waters. This trail of
cloudiness and moisture is forecast to remain in the area,
resulting in cloudy skies and shower activity during the rest of
the morning and afternoon hours. As Tropical Storm Franklin moves
northward, as suggested by the official track from the National
Hurricane Center, a more typical weather pattern is forecast for
the islands with easterly winds. Tranquil marine conditions would
prevail during the period, with a moderate risk of rip currents
for the north-exposed beaches today.

&&

.SHORT TERM... Today through Monday...

The tail from Tropical Storm Franklin is lingering over the region
and scattered to numerous showers with strong thunderstorms
redeveloped along a line from the Mona Passage into east/southeast
PR. The Doppler radar estimated up to 5 inches in Patillas and
Maunabo, and up to 3 inches in Ponce and Salinas. Any additional
shower development along the southern and eastern sections of PR may
lead to flash flooding and mudslides in areas of steep terrain. A
Flash Flood Warning remains in effect for the municipalities of
Arroyo, Guayama, Maunabo, and Patillas through 630 AM AST. Rivers
across these areas were running close to minor flood stage. For the
rest of the day expect the moisture plume to linger across the
region, and southerly winds should push fragmented low-level
moisture across portions of PR, as well across Vieques, Culebra and
the northern USVI.

For the rest of the short term period, normal to above normal
precipitable water content(2.00-2.30 inches) could linger over the
region through late Sunday night, and 500 mb temperatures should
remain between minus 6-7 degrees Celsius, providing unstable
conditions aloft. As TC Franklin continues to strengthens and slowly
move northwards, expect veering of winds and abundant tropical
moisture over the islands. The sea breeze is expected to develop
along the northern coastal areas of PR, and this should enhance
convective activity along the northern slopes and coastal areas of
PR. Today, particularly over San Juan and vicinity and over north
central PR on Sunday. A drier air mass is expected to move from the
east/southeast on Monday, and this should limit the areal coverage
of showers over land areas. Max temperatures could reach the low
90s, if there is a break in clouds between the late morning and
early afternoon hours. Southerly winds and high moisture content
should keep warm to hot temperatures along the urban and lower
elevations of the coastal municipalities of all islands.
&&

.LONG TERM...Tuesday through Saturday...

A variable weather pattern will prevail for the long-term period.
As tropical storm Franklin moves northward far away from the
Caribbean, a building surface high pressure over the western
Atlantic will re-establish the easterly trade winds across the
area. This pattern will introduce a more summer-typical weather
pattern across the islands, with the usual morning pesky showers
followed by the western interior showers for Tuesday. By
Wednesday, tropical moisture, now located just a few miles east of
the Lesser Antilles, will be dragged by the surface winds and
increase the frequency of shower activity across the islands.
According to the latest run from the Gálvez-Davison Index (GDI),
there is potential for isolated to scattered thunderstorms across
the interior in the afternoon.

The bulk of the humidity will be out of the region by Thursday,
leaving PWAT values in the climatological normals over the islands.
However, the proximity of a mid-level (700-500 MB) trough will
enhance the vertical development on Thursday into early Friday
across the local waters and west Puerto Rico. By Friday, enough
moisture will cover the CWA again as a tropical wave reaches the
islands. So far today, PWAT values will go to 2.1 inches, and 500
MB temperatures will round in the -6 to -7 degrees. For the U.S.
Virgin Islands, a typical summer pattern is forecast for the whole
period, with the usual pesky brief passing showers in the
mornings and variable conditions in the afternoons.

&&

.AVIATION...

Mainly VFR conds at all terminals through the period. However,
SHRA/TSRA will continue to affect the coastal waters of PR and the
USVI due to outer band from TS Franklin. Mtn top obscd over
eastern PR and BKN-OVC lyrs btw FL050-FL150 will continue throught
the day. Sfc wnds S-SW at 5-10 kts with higher gusts near
convective activity.

&&

.MARINE...

Light to moderate southerly winds will prevail due to the
Tropical Storm Franklin, now 300 miles north of San Juan, PR. This
system is forecast to continue a northward movement as suggested
by the official track from the National Hurricane Center.
Therefore, mostly tranquil marine conditions will prevail with
seas up to 5 feet across all the waters and winds up to 15 knots.
Although marine conditions are mostly favorable, localized choppy
to hazardous marine conditions are expected near the heavy showers
and thunderstorms from the external bands of Franklin affecting
the area today. Therefore, mariners are urged to stay tuned for
marine statements. There is a moderate risk of rip currents across
the north expose beaches of PR, for the rest of the coastal areas
the risk will remain low.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Mon Aug 28 2023

.SYNOPSIS...Southeasterly trades and hot temperatures will continue
for the next couple of days, with urban and coastal areas reaching
Heat Advisory criteria. A surge in low-level moisture and a
tropical wave moving across the Caribbean waters is expected by
midweek. However, a weak Saharan Air Layer (SAL) will reach the
area at the same time causing hazy skies. Another tropical wave
and stronger SAL are expected to reach the eastern Caribbean
during the weekend.


&&

.SHORT TERM...Today through Wednesday...

Fair weather prevailed across all the islands late into the early
morning hours. Satellite Imagery only showed a few clouds moving
over St. Thomas, and no significant rainfall activity was
observed. Although conditions were calm, overnight temperatures
were in the upper 70s to the lower 80s across the coastal areas
and in the low to mid 70s across the mountains.

For the rest of the morning, all the islands will enjoy mainly clear
to partly cloudy skies with good periods of sunshine. Given the lack
of widespread cloudiness, the southeasterly winds, and the humidity
available, heat indices will climb to 108 to 111° degrees across all
the north and western coastal areas. For the east, south, and urban
sections, including the vicinity of Caguas, heat indices will remain
at up to 107 degrees. Around mid-day, the diurnal heating and the
local effects will trigger localized shower activity across the
northwestern quadrant and north-central areas. The heaviest activity
might result in gusty winds near the showers, hazardous driving
conditions, and ponding water in roadways and poor drainage areas.
Tuesday is going to be the transitional day; in the morning, average
PWAT values, resulting in a very typical summer day, but in the mid-
afternoon, the arrival of an easterly perturbation will increase the
water content across the islands. The surface pattern will be
replicated at the mid-levels, with a trough resulting in some
unstable conditions across the CWA. Therefore, starting from late
Tuesday into Wednesday, weather conditions will deteriorate.
Residents can expect an increase in the frequency of the shower
activity, with the advective pattern in the morning across the
windward sections, followed by afternoon activity. The showers will
focus more on the interior and western interior due to the easterly
trade winds resulting from a building high pressure extending from
the central Atlantic to the northeastern Atlantic.

.LONG TERM...Thursday through Monday...

TC Idalia over the western Atlantic and a weak surface high
pressure across the central Atlantic will maintain light to
moderate east to southeast trades through the period. Precipitable
water content is expected to fluctuate between 1.75-2.00 inches
and the 500 mb temperatures is forecast to remain close to minus
6 degrees Celsius. Therefore, a seasonable weather pattern is
expected, with trade wind showers moving at times across the USVI
and eastern sections of PR during the nighttime and isolated
thunderstorms developing each afternoon over west/northwest PR.
However, a Saharan Air Layer followed by a tropical wave are
expected to dominate the weather conditions during the weekend.


&&

.AVIATION...VFR conditions will persist across the TAF sites during
the period. Winds will continue from the southeast at 10 knots or
less, increasing at 28/14Z up to 15 knots with sea breeze
variations. Some brief VCSH are expected over TJBQ at 28/18z to
28/22Z due to the afternoon showers.


&&

.MARINE...Small pulses of a northerly swell will arrive by
midweek, resulting in a moderate risk of rip currents along the
northern beaches of Puerto Rico. Seas will range between 2 and 4
feet in general, and trade winds with a southerly component should
continue between 10 and 15 knots for the next few days.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
359 AM AST Thu Aug 31 2023


.SYNOPSIS...
Another hot day with excessive heat indices is anticipated for
Puerto Rico and also for the Virgin Islands. Rainfall activity
should be limited to local effects in the afternoon, and mostly
for western Puerto Rico and sections of the San Juan metro area.
Saharan dust will reach the islands latter in the week, so skies
will turn hazy. A northerly swell could reach the islands by
midweek, although seas are expected to remain at 6 feet or less.


&&

.SHORT TERM...Today through Saturday...

Calm weather conditions prevailed overnight with traces of
suspended Saharan Dust Particles. The low-lying areas had low
temperatures in the low 80s and upper 70s, while the mountains
observed lows in the mid and low 70s. Winds continue from the ESE
at around ten mph.

We expect another warm and hot day for the U.S. Virgin Islands
and the low-lying urban areas in Puerto Rico. GOES-E Total
Precipitable Water derived data indicated abundant near-normal to
above-normal moisture content. This moisture, combined with the
maximum air temperatures, will result in heat indices mainly
greater than 107 degrees Fahrenheit. Therefore, Excessive Heat
Warnings are in effect for the USVI, Vieques, Culebra, and from
San German (along the north coast) to Carolina, and Heat
Advisories for the remaining low-lying areas. The warm spell may
extend through Saturday afternoon.

The seasonal weather pattern will result in the typical periods
of sunshine and mostly clear skies, with the arrival of a few
passing showers across the windward sections each night and
morning. The afternoon convection will develop across western
Puerto Rico, driven by sea breeze fluctuations, local effects, and
excessive heat. Traces of suspended dust particles will continue
to be advected across the Northeast Caribbean, increasing by the
weekend. A weak tropical wave may approach the eastern Caribbean
basin with its bulk of moisture well to the south of USVI and PR
by early Saturday morning.


&&

.LONG TERM...Sunday through Friday...

Low to mid level ridge will drive the steering wind from the
southeast on Sunday through Tuesday. Then, as the high moves just
north of the local islands, the trade winds will shift from the
east. On these days, moisture appear limited, and confined to the
lower levels of the atmosphere, as the mid level ridge maintains a
dry air mass at those levels. This air mass will contain some
Saharan dust too, so skies will be hazy. Even with the lack of
dynamics, strong heating should be enough to fire up a few showers
each afternoon, but mainly for western areas in Puerto Rico. Other
areas may receive a shower or two, dragged by the trade winds, but
with no significant rainfall accumulation. By the end of the
workweek, some moisture may reach the islands, increasing the
potential for showers. In general, a seasonal pattern, with
summer-hot temperatures should prevail for at least the first
couple of days of September.

&&

.AVIATION...
VFR conditions will dominate the local flying area. HZ will
persist but with P6SM. SHRA/+TSRA will develop near JBQ around
31/16-22z, producing gusty winds and frequent lightning across the
interior and NW-PR. Winds will be mainly at 10 kt or less out from
the ESE, then after 31/13z, will fluctuate between 10 and 15 kt,
but under the sea breeze influence.

&&

.MARINE...
No significant marine events are forecast for the next two days,
except for locally stronger winds creating choppy seas. A
northerly swell associated with Hurricane Franklin could reach the
islands by midweek, but seas should remain at 6 feet or less. The
risk of rip currents is moderate for the northern beaches of
Puerto Rico.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
355 AM AST Fri Sep 1 2023

.SYNOPSIS...
The month of September will begin with a warmth note, as heat
indices are expected to be around 108 to 111 degrees for many
urban and coastal areas in Puerto Rico and the U.S. Virgin
Islands. Afternoon activity may lead to urban and small stream
flooding, especially along western Puerto Rico. A tropical wave is
expected to reach the islands this weekend, with the best
potential for rain on Sunday. Saharan dust is expected to reach
the islands by Monday, lingering throughout most of the workweek.

&&

.SHORT TERM...Tonight through Sunday...

Showers embedded in the winds moved overnight across the U.S.
Virgin Islands and Puerto Rico windward sections. Skies were
mostly clear with traces of suspended Saharan dust particles under
an east-south wind flow. The low-lying areas had low temperatures
in the low 80s and upper 70s, while the mountains observed lows
in the mid and low 70s.

The warm and hot conditions will continue for the U.S. Virgin
Islands and the low-lying urban areas in Puerto Rico, with heat
indices up to 111 degrees Fahrenheit. As a result, a Heat Advisory
is in effect for the USVI, Vieques, Culebra, and along the north
from San German to Carolina. Neither Warnings nor Advisories are
in effect for the rest of the urban and low-lying areas; they can
expect above-normal heat indices to create uncomfortable
conditions. The excessive heat threat may extend into the weekend.

The U.S Virgin Islands and Puerto Rico will be under the typical
weather conditions consisting of plenty of periods of sunshine and
mostly clear skies, with the arrival of a few passing showers
across the windward sections each night and morning. The sea
breezes, excessive heat, and local conditions will trigger
afternoon convection across western Puerto Rico, resulting in
flooding rains each day. The traces of suspended dust particles
may enhance the thunderstorm intensity and will continue to be
advected across the Northeast Caribbean, increasing the
concentrations by the weekend. By Saturday, the winds will shift
more from the southeast, and a weak tropical wave is forecast to
approach the eastern Caribbean basin with its bulk of moisture
south of USVI and PR. Sunday may be the wettest day of the short-
term period as the tropical wave moves near the region, influenced
by the possible track of Idalia at a distant and safe position
from the islands.

&&

.LONG TERM...Monday through Saturday...

A low to mid level high pressure will be driving winds from the
southeast by the start of next workweek. The trade winds will also
drag a Saharan Air Layer along the islands, resulting in hazy
skies through much of the workweek. Moisture will be mainly trap
at the lowest 850 mb of the atmosphere, with dry air from 850-400
mb. No significant rain events are anticipated this week, but
patches of moisture will still reach the islands at times,
resulting in a typical pattern of passing showers reaching the
Virgin Islands and eastern Puerto Rico early in the day, and
showers with isolated thunderstorms for the interior and western
Puerto Rico. By Friday, both global models show increasing
moisture, but with different upper patterns. The GFS has ridging
aloft, while a trough is observed in the ECMWF. Regardless, at
least some increase in shower activity can be expected by then,
lingering into the early weekend.

&&

.AVIATION...

Once again, expect VFR conditions for the local flying area with
HZ but with P6SM. SHRA/+TSRA will develop near JBQ around
01/16-22z, producing gusty winds and frequent lightning across the
interior and NW-PR. Winds will be mainly at 10 kt or less out from
the ESE, then after 01/13z, will fluctuate between 10 and 15 kt,
but under the sea breeze influence.

&&

.MARINE...
Tranquil marine conditions are expected today, but seas could
begin to increase on Sunday as a northerly swell arrives. So far,
the guidance suggest seas staying below 6 feet, but the trend will
need to be watch for any needed adjustments.

So far, the swell looks to be around 5 feet with a period of 11
seconds, which should at least trigger a high rip current risk
for the northern coast of the islands. For today, the rip current
risk is generally low, with a moderate risk for some beaches in
the northern coast of Puerto Rico and for Culebra.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Sat Sep 2 2023

.SYNOPSIS...

A Saharan Air Layer (SAL) will surround a weak tropical wave
moving across the eastern Caribbean today and tomorrow. Suspended
Saharan Dust particles will increase somewhat across the islands
of Puerto Rico and the U.S. Virgin Islands this afternoon and
onward. Sunday may be the wettest day of the short-term period as
the tropical wave moves near the region, influenced by Idalia at a
distant and safe position from the islands. Next week looks dry
and hazy due to the SAL, but we could transition to a more wet and
unstable weather pattern due to a tropical wave by next Friday
into next weekend. Another tropical system may approach the region
by early next week.

&&

.SHORT TERM...Today through Monday...

Small and weak patches of moisture have been moving across the
islands tonight, with isolated showers observed along eastern Puerto
Rico and the U.S. Virgin Islands. Rainfall accumulations were very
light. Temperatures dropped into the low 80s and upper 70s at lower
elevations and into the upper 60s in the mountain.

The environment today will be dominated by a weak Saharan Air Layer
and a tropical wave moving over the eastern Caribbean Sea. The bulk
of the moisture from the wave will remain over the water, but
satellite-derived precipitable water products do show another small
pocket of enhanced moisture approaching from the east that should
bring some passing showers today. The steering flow is from the
southeast today, due to a weak high pressure located over the
central Atlantic. These ingredients should combine to generate some
showers along the north-interior and northwest Puerto Rico in the
afternoon hours.

As the tropical wave moves across the Caribbean, more moisture will
filter into the region by early Sunday, with the potential for early
showers along the southern coast of Puerto Rico. The high resolution
models show modest rainfall accumulation, but wet roads may be
observed early in the day, and another round of afternoon activity
for the northwestern quadrant of Puerto Rico. Upper dynamics do not
favor widespread showers, although an isolated strong thunderstorm
cannot be ruled out. Once the wave departs, a drier air mass will
filter in, with Saharan particles embedded too. Therefore, the
environment will become unfavorable for rainfall activity, as hazy
skies prevail on Labor Day (Monday).

In terms of temperatures, we are not expecting a relief from the
above normal heat that has been punishing the islanders, so expect
excessive heat indices (above 108F) every day, especially from 9 AM
to 5 PM AST.

.LONG TERM...Tuesday through Monday...

Global models suggest drier-than-normal conditions from Tuesday
to late Thursday night or early Friday morning. Additionally,
GEOS-5 with Dust Aerosol Optical Thickness (AOT) indicates the
presence of traces of suspended dust particles through at least
Friday, when a tropical wave will bring a moist air mass and
unstable pattern. The warm-to-hot spell may continue daily with
heat indices between 102 and 112 degrees Fahrenheit or even
greater. Regardless of the dry air mass, the influence of the sea
breeze combined with pockets of moisture, diurnal heating, and
local effects may result in afternoon convection each day, mainly
across western Puerto Rico. Although some showers may affect the
Virgin Islands, they will experience more sunshine and scorching
temperatures than rainfall activity.

Both global models (GFS and ECMWF) suggest the region
transitioning to a wet and unstable weather pattern by Friday into
Monday. A tropical wave could affect the islands on Friday,
followed by an area of subsidence ahead of a more vigorous
tropical system around Sunday or Monday. Model guidance indicates
discrepancies associated with the motion and intensity of early
next week's tropical system. However, the latest GFS 02/00z and
ECMWF 02/00z solutions tend to develop a tropical system near the
Northeast Caribbean. That said, there is still a lot of
uncertainty regardless of this system due to how far in the
forecast it is. As we approach the peak of the Atlantic Hurricane
Season, we encourage all of you to keep track of the weather
conditions.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions expected to prevail. A few SHRA
will move across the Caribbean waters, but with little to no impact
to operations. Additional SHRA and isolated TSRA expected after 17Z
for NW PR and around the Cordillera Central, causing mountain
obscuration. Brief periods of reduced VIS and low ceilings also
expected from 17-22Z for TJBQ. Winds will be from the SE at 8-13 kts
with stronger gusts.

&&

.MARINE...

A northwesterly swell will arrive later this afternoon, suddenly
deteriorating coastal conditions. Marine guidance is
underestimating this swell, but 41046 buoys detected this swell
rapidly approaching the region. This swell was created by Idalia
and the tropical system far to the north over the Atlantic Ocean.
Mariners can expect seas between 3 and 5 feet this morning,
rapidly increasing to 4 to 6 by this afternoon, and near Small
Craft Advisory conditions by Sunday.

Beachgoers, the risk of rip currents is moderate for the north and
northwest-facing beaches in Puerto Rico and the U.S. Virgin
Islands and will turn high this afternoon into tomorrow.

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
442 AM AST Sun Sep 3 2023

...New SYNOPSIS, AVIATION, MARINE...

.SYNOPSIS...
Issued at 420 AM AST Sun Sep 3 2023

Coastal conditions from Rincon to Fajardo, Culebra, St Thomas, and
St John are hazardous due to life-threatening rip currents and
dangerous breaking waves. The tropical wave will move northward,
pooling plenty of moisture over Puerto Rico and the U.S. Virgin
Islands due to tropical and extratropical systems off to the north
over the Atlantic Ocean. A Saharan Air Layer (SAL) will move in
from the east and affect the Northeast Caribbean tonight and early
Monday, lasting throughout the work week. The hot spell will
return on Monday and stay through at least next Friday, followed
by a potential shift to a wetter and more unstable weather due to
a low-level disturbance. The National Hurricane Center monitors a
tropical system near the Cabo Verde Islands that may approach the
region early next week.

&&

.SHORT TERM...Today through Tuesday...

The moisture field of a tropical wave is evident just south of
Puerto Rico and a significant moisture gradient now reaching the
Leeward Islands. The most significant activity of the wave will
remain over the Caribbean Waters, but since last night, some showers
managed to reach the southern and eastern municipalities of Puerto
Rico, Vieques, Culebra and all of the U.S. Virgin Islands. The
heaviest showers was observed over St. Croix, and from Naguabo to
Ceiba, with a brief period of reduced visibilities observed in the
international airport.

Cloudiness and passing showers will continue to move in along the
area, with the more frequent activity anticipated-again- for eastern
and southern Puerto Rico. Wet roads as well as ponding of water on
low-lying areas can be anticipated in these areas. Later in the
afternoon, stronger showers and thunderstorms could develop in the
western half of Puerto Rico, with frequent lightning and an elevated
risk for urban flooding and water surges along the rivers. Then,
the drier air mass currently over the Leeward Islands will begin to
filter in. This air mass also contains Saharan dust, so skies will
be hazy and rain will taper off.

Throughout the forecast period, a surface to mid levels high
pressure just northeast of the local islands will maintain a deep
layer flow out of the southeast, with a trade wind cap inversion
developing at around 850 mb. Since moisture will be trapped at the
lower levels, precipitable water values will drop below normal, with
a noticeable reduction of shower activity in the area. Regardless,
strong heating should be enough to fire up some showers in the
northwestern quadrant of Puerto Rico.

Today, the cloud coverage should limit the brutal heat indices that
have been punishing the islanders. It will not be cool though, with
values still ranging from 102 to 107 degrees. With more sunshine
anticipated for Monday and Tuesday, and with 925 temperatures over
two standard deviation above normal, temperatures and heat indices
will soar once again. Heat advisories or excessive heat warnings may
be required these days.

&&

.LONG TERM...

Global models suggest drier-than-normal to near-normal conditions
from Labor Day through Wednesday or early Thursday. Furthermore,
GEOS-5 with Dust Aerosol Optical Thickness (AOT) indicates the
presence of traces of suspended dust particles through at least
Friday, when a low-level disturbance will bring a moist and
unstable weather pattern. Regardless of the lack of moisture at
the beginning of the upcoming work week, the sea breeze combined
with pockets of moisture, diurnal heating, and local effects may
result in afternoon convection with isolated strong thunderstorms
each day, mainly across western Puerto Rico. Although some showers
may affect the Virgin Islands, they will experience more sunshine
and scorching temperatures than rainfall activity. The hot spell
will possibly last through Thursday, with daily heat indices
between 102 and 112 degrees Fahrenheit or even greater, after
which there is a possibility of a shift towards a more unsettled
and rainy weather pattern.

The National Hurricane Center monitors a tropical wave near the
Cabo Verde Islands. Environmental conditions are conducive for
this system to become a Tropical Cyclone through the next week,
with a 70 percent formation chance through the next 7 days. It is
still too early to know for sure the trajectory and intensity
forecast it will have when approaching the Northeast Caribbean
early next week. Therefore, the end of this Long Term Forecast
period is challenging because changes in this system's evolution
will alter the weather conditions we may experience in the
islands. However, as we approach the peak of the Atlantic
Hurricane Season, we must remain vigilant of any potential impacts
on daily operations or plans.&&

.AVIATION...
(06Z TAFS)
Issued at 420 AM AST Sun Sep 3 2023

Mainly VFR conditions expected to prevail. SHRA are moving from
the Caribbean Sea into USVI and southern PR. Brief interruptions
to operations possible for USVI before 16Z, and for TJPS and TJSJ
through much of the period. Isolated TSRA could also develop for
TJBQ after 18Z, with periods of reduced VIS and low ceilings.
Winds will be from the SE at 9 to 14 kts, with stronger gusts,
especially around strong SHRA and TSRA.

&&

.MARINE...
Issued at 420 AM AST Sun Sep 3 2023

Model guidance continues underforecasting the north-
northwesterly swell. Therefore, we manually adjust the marine
forecast following the local buoy network at deep and nearshore
waters. Expect seas between 4 and 7 feet across the Atlantic
Waters and Mona Passage. A Small Craft Advisories is in effect for
the Atlantic Waters from this afternoon through at least early
Tuesday morning.

Mariners with interest across Puerto Rico and the U.S. Virgin
Islands should monitor marine conditions for next weekend as a
tropical wave monitored by the National Hurricane Center and, with
a 70 percent chance of formation in the next 7 days, should move
close to the Northeast Caribbean.

The north-northwesterly swell creates hazardous coastal conditions
due to life-threatening rip currents and breaking waves along the
north-facing beaches from Rincon to Fajardo, Culebra, St Thomas,
and St John.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Wed Sep 6 2023


.SYNOPSIS...
Remnants from a northerly swell will continue to cause hazardous
beach conditions over northern Puerto Rico and Culebra. Excessive
heat will continue to impact the islands, but to a lesser extent
than in previous days. The National Hurricane Center is
monitoring Tropical Storm Lee as it moves over the Atlantic basin.
Marine and coastal conditions, along with weather conditions could
deteriorate this weekend as Lee passes north of the area. The
users are advised to monitor the evolution of Lee through the
next several days.

&&

.SHORT-TERM...Today through Friday...

Today's hazard risks focus on excessive heat at limited threat
levels and excessive rainfall at limited to elevated threat levels.
Both hazard risks will continue throughout the rest of the workweek.

Radar and satellite imagery indicated fair weather conditions across
the region, with minimal cloud cover and lack of showers. Overnight
low temperatures fell to around 68 degrees across higher elevations
of the interior and about 80 degrees across lower elevations. Winds
were generally light and variable but calmer further inland.

A multi-level high pressure system east-northeast of the region, and
dominant feature, will yield low-to-mid level east-southeast winds
at 5-15 mph today, gradually backing from the east on Thursday as
the system slowly moves away and dissipates over the western
Atlantic. By Thursday night into Friday, winds will become
progressively more from the east-northeast, influenced by Tropical
Storm or potentially Major Hurricane Lee, as it moves northeast of
the local islands. Mid-level ridging, linked with the above-mentioned
high pressure, will hold over the region, supporting a trade wind
cap around the 850 mbar layer and unfavorable conditions for deep
convective development. Steered by this general wind flow,
shallow tropical moisture will gradually replace a relatively
drier airmass accompanied by light concentrations of Saharan Dust
particles that have persisted across the region during the last
few days. This transition will echo in Precipitable Water (PWAT)
values across the region, increasing from two standard deviations
(1.1-1.2 inches from the 6/12Z sounding) to slightly above one
standard deviation (1.7- 1.8 inches) below climatological moisture
levels from this afternoon into Thursday, as suggested by
satellite-derived PWAT. Following the most recent model guidance
and in close agreement with satellite- derived PWAT, a narrow
patch of drier air will quickly follow, causing PWAT to fall again
close to two standard deviations below climatological moisture
levels by Thursday night. Still, this will be short-lived, with
abundant moisture steered by a low-level disturbance causing PWAT
to quickly rise to around one standard deviation (2.0-2.1 inches)
above climatological moisture levels between Friday afternoon and
late Friday night. Prevailing southeasterly winds and well above
normal 925mb temperatures will lead to warm-to-hot conditions
through Friday, with daytime high temperatures peaking into the
lower 90s and heat index values likely to exceed 108 degrees
across some areas.

Following the described scenario, expect a slight increase in shower
activity today, mainly from afternoon convective development. In
response to the persistent weak steering flow (5-15 mph), rains from
the anticipated slow-moving showers with possible isolated
thunderstorms will likely lead to elevated excessive rainfall hazard
risks, resulting in urban and small stream flooding. Today's
activity should cluster across the central interior west-
northwestward to the far western and northwestern sections of Puerto
Rico, with secondary rainfall maxima possible across northeastern
Puerto Rico, including portions of the San Juan metropolitan area.
Across the U.S. Virgin Islands and the local islands, expect
variable weather conditions with a mixture of sunshine and the
occasional passing shower in the afternoon. Warm-to-hot conditions
are likely today, with prolonged warmer conditions in rain-free
areas across northern Puerto Rico, Vieques, and Culebra, where Heat
Advisories are in place. Heat index values of 102-107 degrees are
likely in other lower elevations and urban areas. For details, refer
to the Non-Precipitation Warnings, Watches, and Advisories product
(NPWSJU) issued by the National Weather Service, San Juan office.


&&

.LONG TERM...Saturday through Wednesday...

The long-term forecast will be mostly modulated by current Tropical
Storm Lee as it moves over the tropical Atlantic. According to the
official forecast track and intensity from the National Hurricane
Center, Lee will become a major hurricane on Friday and pass to
the north of Puerto Rico by late Sunday. The center of
circulation, or eye, is expected to remain between 250 to 300
miles north of the islands. Although Lee is forecast to become a
large hurricane, its tropical storm wind field will remain mostly
far from the forecast area. So far, we have 10% to 20% probability
of experiencing tropical storm force winds of less than 39 mph,
with less percentage associated with higher wind intensities.
Therefore, we are not expecting a direct impact from Lee. However,
Lee will pass sufficiently close to influence local weather
patterns, particularly by shifting wind direction and speed and
increasing moisture content to above-normal levels across the
northeastern Caribbean.

Winds will become light and shift from the northeast, north, and
northwest this weekend. For now, global models are showing less
cloud coverage throughout the weekend, which could enhance diurnal
heating effects during afternoon hours. By Sunday, it seems that we
will also be under the influence of a col region as Lee passes
northeast of the local islands. Therefore, the weekend could observe
explosive deep convective activity each afternoon, first developing
across the Cordillera Central and afterward moving along coastal
regions depending on outflow boundary patterns. If this scenario
plays out, expect urban and small-stream flooding with this
activity, with the potential of flash flooding events in localized
areas. Gusty wind conditions are possible with the strongest
thunderstorms, which could cause minor damage to tree limbs and
blowing of light, unsecured objects. The highest uncertainty will be
how close the subsidence region from the periphery of Lee will reach
the local islands this weekend, diminishing convective activity
across the region.

By early next week, squally weather is possible as Lee continues
moving northwestward. The rest of the week could also observe a
continuation of unsettled weather conditions as Lee continues to
induce southerly winds across the islands and pull plenty of
tropical moisture. However, this will strictly depend on how Lee
behaves after it passes north of the local islands. Hot and muggy
conditions will linger with these southerly winds. Continue to
monitor the NHC and the NWS San Juan forecast for further updates
as this event unfolds.

&&

.AVIATION...Mainly VFR conditions will prevail during the next 24
hours. However, TSRA/SHRA could result in brief MVFR conditions
across TJBQ, TJSJ, and USVI terminals between 06/16-22Z. Light to
calm and variable winds becoming ESE and increasing to 10-15 knots
with higher gusts and sea breeze variations between 06/14-22Z. Winds
will become lighter to calm and variable again after 06/22Z.

&&

.MARINE...
Remnants from a northerly swell will continue to cause rough seas
across the Atlantic regional waters, although it will remain
under Small Craft Advisory criteria. The northwestern and northern
beaches of Puerto Rico and Culebra continue to be hazardous for
beachgoers, due to hazardous breaking waves. Therefore, a high
risk of rip currents is in effect for these areas.

[cycloneye]

Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
536 AM AST Thu Sep 7 2023


.SYNOPSIS...
Expect variable weather conditions with mixed periods of sunshine
and rain today, and peak rain activity generated from afternoon
convective development. High risk of rip currents will persist
today for north-facing beaches of Puerto Rico. Marine and coastal
conditions will turn extremely hazardous this weekend as Hurricane
Lee passes north of the area. Excessive heat hazard will increase
next week as winds turn southerly over the local islands.

&&

.SHORT-TERM...Today through Saturday...

Today's hazard risks focus on excessive heat and lightning at
limited threat levels and excessive rainfall at limited to elevated
threat levels. All three hazard risks will persist through the
weekend.

Radar and satellite imagery indicated fair weather conditions early
in the evening, followed by increased shower activity after
midnight. Some showers moved over eastern Puerto Rico, Vieques,
Culebra, and the U.S. Virgin Islands, leaving around half an inch
between Arroyo and Guayama. Overnight low temperatures fell to about
68 degrees across higher elevations of the interior and about 81
degrees across lower elevations. Winds were generally light and
variable but calmer further inland.

Although dissipating as it meanders across the western Atlantic and
north of the local islands, a multi-level high pressure system will
maintain low-to-mid-level east-southeast winds at 5-15 mph today.
Winds will become progressively more from the east-northeast to the
northeast Friday into Saturday as Hurricane Lee moves well east and
northeast of the local islands. Mid-level ridging, linked with the
above-mentioned high pressure and the resulting trade wind cap
inversion, will gradually weaken today, yielding marginal conditions
for deep convective development. Following satellite-derived Total
Precipitable Water (PWAT) and in agreement with the most recent
model guidance, a patch of shallow tropical moisture will continue
to stream across the region, with PWAT increasing to slightly above
one standard deviation (1.7-1.8 inches) below climatological
moisture levels this afternoon. Quickly after that, a narrow patch
of drier air will follow, causing PWAT to fall close to two standard
deviations (1.4-1.5 inches) below climatological moisture levels
tonight. Still, this will be short-lived, and abundant tropical
moisture steered by a low-level disturbance will envelop the
forecast area from Friday morning, causing PWAT to hold at around
one standard deviation (2.0-2.1 inches) above climatological
moisture levels through Saturday. Slightly above normal 925mb
temperatures in a high-moisture environment will lead to warm-to-hot
conditions, with daytime high temperatures peaking into the lower
90s and heat index values likely to exceed 108 degrees, particularly
across rain-free areas on Thursday and Saturday.

Following the described scenario, expect variable weather conditions
with mixed periods of sunshine and rain today, and peak rain
activity generated from afternoon convective development. Given the
persistent weak east-southeast steering flow, moderate to locally
heavy rains from the anticipated slow-moving showers and isolated
thunderstorms will likely lead to elevated excessive rainfall hazard
risks, resulting in urban and small stream flooding. Isolated flash
floods and mudslides are possible, particularly in areas that
experienced rains on previous days. Today's activity should cluster
across the interior to northwestern sections of Puerto Rico, with
showers spreading across surrounding areas late this afternoon.
Secondary rainfall maxima are possible across eastern Puerto Rico,
including portions of the San Juan metropolitan area. Across the
U.S. Virgin Islands and the local islands, expect variable weather
conditions with a mixture of sunshine and the occasional passing
shower throughout the day. With the entrance of drier air, fair
weather conditions with the occasional passing shower over windward
areas are likely tonight, followed by more frequent showers with
thunderstorms on Friday and Saturday. Warm-to-hot conditions are
expected again today, with prolonged warmer conditions across
northern and eastern sections of Puerto Rico, Vieques, and Culebra,
where Heat Advisories are in place between 10 AM and 5 PM AST.
Elsewhere, particularly across lower elevations and urban areas,
heat indices of 102-107 degrees, where heat exhaustion is possible
with prolonged exposure. For details, refer to the Non-Precipitation
Warnings, Watches, and Advisories product (NPWSJU) issued by the
National Weather Service, San Juan office.

&&

.LONG TERM...Sunday through Thursday...

The official NHC forecast track and intensity have not changed
much and is expected to continue on track as Lee remains north of
the local islands. Tropical storm force wind probabilities
continue at 10% to 20% for the local area. Therefore, as mentioned
in the previous discussion, confidence level is high regarding
track forecast and we don't expect a direct impact from Hurricane
Lee this weekend. However, the anticipated weather scenario for
the long-term forecast period remains uncertain since it will be
linked to the dynamic pattern associated with the outermost area
of Hurricane Lee as it crosses the Atlantic waters north of the
forecast area. Although the northeastern Caribbean will be
engulfed in above-normal moisture content through the cycle from
the proximity of Hurricane Lee, rainfall accumulations from model
guidance remain unimpressive.

For now, Sunday seems the wettest of the long-term forecast, with
variations in shower and thunderstorm activity throughout the
week. Areas affected by showers and thunderstorms will depend on
the changing steering wind. A col region will develop over the
area promoting convective activity to develop over the Cordillera
Central, mostly in the afternoon accentuated by local and diurnal
effects. Any shower and thunderstorm activity will move fairly
slowly, enhancing rainfall accumulations in certain areas. This
pattern will lead to elevated hazard risks from lightning and
excessive rainfall. For the rest of the week, winds will shift
counterclockwise, from the northwest on Monday to southwest by
mid- week. Southwestern steering winds will increase the risk of
any strong thunderstorm moving over the San Juan Metropolitan area
in the afternoon hours. However, as indicated above, uncertainty
persists as models continue to change from cycle to cycle,
although we are not expecting widespread activity across the
islands. Other potential hazard risks include excessive heat, at
limited to elevated risk levels, particularly by mid-week of next
week as weak southerly winds persist over the region. Stay tuned
for further updates on the forecast.

&&

.AVIATION...SHRA could result in brief MVFR conditions across TJSJ,
TJPS, and USVI terminals terminals through 07/14Z. Between 07/17-
23Z, TSRA/SHRA could also result in MVFR to brief IFR conditions
possible across all PR terminals. Light to calm and variable winds
increasing to 10-15 knots with higher gusts and sea breeze
variations between 07/14-22Z. Winds will become lighter to calm and
variable again after 07/22Z.

&&

.MARINE...Dissipating northerly swells and moderate to locally fresh
winds will maintain choppy seas up to 6 feet across most of the
local waters during the next few days. Thus, small craft operators
should exercise caution, particularly near coastal areas during peak
hours of the day. These dissipating swells will continue to generate
life-threatening rip current conditions today for beaches across the
north coast of Puerto Rico, where a High Risk of Rip Currents
remains in place.

Marine conditions will deteriorate by Saturday into early next week
as swells generated by Hurricane Lee affect the local waters.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through this afternoon for PRZ001-002-005-
008-010.

Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for PRZ001-004-005-008-012-013.

High Rip Current Risk until 6 AM AST early this morning for
PRZ012.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Fri Sep 8 2023


.SYNOPSIS...
A surface perturbation pushed by Hurricane Lee is approaching the
region. This will promote shower and thunderstorm activity
throughout the day. Variable weather conditions expected this
weekend as Major Hurricane Lee moves northeast of the area. Marine
and coastal conditions will deteriorate this weekend through next
week.

&&

.SHORT-TERM...Today through Sunday...

Today's main hazards revolve around the risk of excessive rainfall
and lightning, with threat levels ranging from limited to elevated,
and these concerns are expected to persist throughout the weekend.

Analysis of radar and satellite imagery indicates that eastern
Puerto Rico experienced showers during the evening hours, resulting
in minimal radar-estimated rainfall accumulations. However,
conditions improved significantly after midnight, leading to fair
weather under clear skies. Overnight temperatures varied across the
region, with higher elevations in the interior dropping to around 68
degrees while lower elevations maintained temperatures at
approximately 81 degrees. Winds were generally light and variable.

Influence by Major Hurricane Lee's wind field, local winds are
anticipated to shift from the east-northeasterly today, becoming
more northeasterly on Saturday and variable on Sunday due to Lee's
proximity. Despite these variations, the steering flow is expected
to remain light, ranging from 5 to 15 mph throughout the forecast
period.

Based on satellite-derived Total Precipitable Water (PWAT) data and
following recent model guidance, a substantial amount of tropical
moisture, originating from a low-level disturbance and steered by
Lee's outer flow, is forecasted to spread west-southwestward across
the forecast area. This transition will rapidly increase PWAT
levels, exceeding one standard deviation (2.0-2.2 inches) above
normal moisture levels today and continuing through Saturday.
Consequently, expect an increase in showers and thunderstorm
activity each day, clustering across the interior to west-
southwestward sections of Puerto Rico during the afternoons.
Nonetheless, rains may affect most land areas, particularly on
Saturday, which appears to be the most active day during the
forecast period. This showery scenario should persist through the
overnight and early morning hours, with showers accompanied by
thunderstorm activity extending into eastern Puerto Rico and the
U.S. Virgin Islands. The resulting moderate to heavy rains will
likely generate excessive rainfall impacts, including ponding of
water on roadways and poorly drained areas, as well as urban and
small stream flooding, even with nighttime activity. There is also a
potential for localized flash floods and mudslides.

While there is some uncertainty about the evolution of Lee's outer
bands as the system moves well northeast of the local islands, model
guidance suggests that Lee's feeding band will extend into the
northeastern Caribbean starting Sunday night, transporting
significant amounts of tropical moisture into the region. While the
current forecast aligns with this scenario, it calls for a more
conservative approach regarding precipitation probabilities at this
time.

Despite slightly lower temperatures at the 925mb level and
northeasterly winds, there is potential for some relief from the
prevailing warm-to-hot conditions. Still, heat index values could
reach 102-107 degrees, particularly across prolonged rain-free areas.

&&

.LONG TERM...Monday through Friday...

Looking ahead to next week, the prevailing influence of Major
Hurricane Lee will persistently shape the local weather patterns.
Winds will shift from the northwest on Monday culminating in
southeasterly winds by Friday, shifting in a counterclockwise
manner, induced by Hurricane Lee as it moves northward. Although
near-normal to above-normal moisture content will dominate
throughout the week with feeding bands from Lee still present across
the area, the support for convection aloft is anticipated to wane
due to the persistent presence of a mid to upper-level ridge over
the region through at least Wednesday. During this period, 250 mb
heights are expected to remain higher than usual, leading models to
exhibit cautious optimism regarding rainfall, primarily driven by
intermittent afternoon convection stemming from diurnal heating and
local effects. Tuesday and Wednesday may bring an uptick in showers
and isolated thunderstorms to the San Juan metro area, with
prevailing southwest winds.

As Thursday approaches, the GFS Galvez Davison-Index algorithm hints
at Lee's feeder bands reactivating, resulting in an expanded
coverage area of isolated to scattered thunderstorms across the
local islands. This resurgence could be attributed to the
development of an upper-level trough to the northeast of the region
toward the end of the workweek. Additionally, 500 mb temperatures
are projected to decrease to a range of -7 to -8 degrees Celsius,
potentially inducing a more favorable dynamic weather pattern for
the latter part of the forecast period. However, it's important
to note that there remains a high degree of uncertainty due to the
erratic behavior of Lee's feeder bands. Nevertheless, the
persistent above-normal moisture content and the proximity of
Hurricane Lee will heighten the potential for shower and
thunderstorm activity in select areas.

Another potential hazard to be mindful of is the possibility of
excessive heat, with the risk level ranging from limited to
elevated. This concern becomes more pronounced, especially as we
progress into the middle of the upcoming week, given the persistence
of weak southerly winds in the region. For the latest updates, it is
advisable to closely monitor the evolving forecast.

&&

.AVIATION...SHRA could result in brief MVFR conditions across TJSJ
and USVI terminals after 08/13Z and TJBQ after 08/22Z. Between 08/16-
22Z, TSRA/SHRA could result in MVFR to brief IFR conditions
across TJPS. Light to calm and variable winds becoming
northeasterly and increasing to 10-15 knots with higher gusts and
sea breeze variations between 08/14-22Z. Winds will remain
northeasterly but lighter after 08/22Z.

&&

.MARINE...Large swells from Major Hurricane Lee will reach the
regional waters by Saturday morning, and will continue to do so
through next week. Seas of up to 12 feet are possible throughout
this period. For now, Small Craft Advisories are therefore in effect
for the offshore Atlantic waters and Anegada Passage. Rip current
risk will become high during the weekend as Hurricane Lee moves
close to the area.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
502 AM AST Sat Sep 9 2023


.SYNOPSIS...

This weekend, expect variable weather conditions as Major Hurricane
Lee tracks to the northeast of the region. Marine and coastal
conditions are anticipated to worsen from this weekend into the
following week.

&&

.SHORT TERM...Today through Monday...

For the rest of the morning...Isolated to scattered showers will
persist along the northern and eastern sections of PR and the USVI
with mainly isolated showers over the coastal waters. The prevailing
northeast wind flow driven by the broad cyclonic circulation of the
major Hurricane Lee located some 440 miles or so E of the Northern
Leewards overnight, will continue throughout the day. Lee is still
forecast to track west northwest across the Atlantic water and
remain well northeast of the islands during the rest of the weekend,
then continue north of the area late Sunday through Monday.
Northeasterly winds will prevail today then gradually become light
and variable tonight into early Sunday, then more west southwesterly
late Sunday into Monday based on the latest guidance and track of
Hurricane Lee, which will continue to influence the overall local
steering pattern. Overnight low temperatures along the coastal areas
will range in the upper 70s to low 80s, and in the upper 60s to low
70s in higher elevations. High temperature will be in the low to mid
90s along coastal areas with maximum heat indices reaching 108-111
degree along the north and east sections of some of the islands and
between 100-107 degrees elsewhere.

For the rest of today, the continued transport of low level moisture
will be sufficient to support afternoon convection mainly over the
central and west to southwest sections of Puerto Rico. However brief
periods of isolated to scattered afternoon showers cannot be ruled
out in and around the San Juan metro area and the U.S. Virgin
Islands later in the afternoon and during the evening hours.

For Sunday and into Monday expect fairly light and variable winds to
continue as Hurricane Lee is forecast to continue west northwest
across the Atlantic and remain well north of the region while
disrupting the overall circulation across the region. So far recent
guidance and the overall pattern continued to suggest a gradual
increase in moisture content as Lee pulls further north of the
region while lifting fragments of trailing moisture across the
region late Sunday into Monday, as winds become more southwesterly.
Although there still remains uncertainty in the forecast for
rainfall amounts across the region during the period, expect
sufficient moisture transport and pooling across the area each day
for early morning and afternoon convection. Some showers and the
thunderstorm activity will produce periods of locally heavy rains at
times, as occasional feeder bands and the trailing moisture plume
from Hurricane Lee will make their way across the region. Please
continue to stay informed with the latest advisories and updates
from the National Hurricane Center and our local forecast office WFO
San Juan PR and also info regarding the marine and coastal
conditions which are forecast to rapidly deteriorate over the rest
of the weekend into early next week.

&&

.LONG TERM...Tuesday through Saturday...

We continue to closely monitor Major Hurricane Lee as it progresses
in the Atlantic waters, with the latest forecast indicating that the
eye of the hurricane is expected to be located around or more 300
miles north-northeast of Puerto Rico by Tuesday. While Lee will
continue moving northward throughout the week, there are potential
indirect impacts associated with the outer bands that warrant
attention.

As mentioned in previous discussions, the erratic movement of the
feeder bands from Lee is adding uncertainty to the rainfall
forecast, particularly amounts and locations. For the latter, the
heaviest rains will depend on the wind pattern which will be mostly
southwesterly to southerly through at least the end of the workweek.
This could mean that the southern municipalities and St. Croix may
be affected mostly late night through morning hours, while interior
and northern municipalities of Puerto Rico may observe the greatest
rainfall in the afternoons.

The models consistently indicate the likelihood of a mid- to upper-
level ridge during the initial part of the forecast period, which
could potentially suppress convective activity to some extent across
the islands. By the end of the workweek, a TUTT will approach from
the northeast with 250-height fields and 500 mb temperatures falling
to below-normal levels. Therefore, conditions aloft may turn
conducive for convective activity by the latter part of the week.
Certainly, the ECMWF and GFS Galvez Davison-Index algorithms
indicate the possibility of feeder bands reactivating by the end of
the workweek. Should this situation materialize, areas including
northeastern Puerto Rico, Vieques, Culebra, and the northern Virgin
Islands could experience elevated impacts from these feeder bands.
This could potentially lead to localized flooding and flash
flooding, especially in low-lying and flood-prone areas. Minor wind
damage is possible as wind gusts from the strongest thunderstorms
may be possible. It is essential to exercise caution when traveling
and avoid flooded roadways. Nevertheless, it is essential to
emphasize that the forecast carries significant uncertainty, as
mentioned earlier.

Throughout the week, heat-related effects will persist due to light
southerly winds and elevated humidity levels, which will in turn
raise the heat index values across the islands. Some relief could be
felt by next weekend as winds return more easterly across the
northeastern Caribbean. Continue to monitor updates from the
National Hurricane Center and WFO San Juan for the latest
information.

&&

.AVIATION...

VFR conds at all terminals and en route btw the local islands.
Due to the moderate low level NE wind flow, expect SCT SHRA with
Isold TSRA ovr ATL waters and btw E PR and the USVI til 09/13Z.
Brief Mtn top obscr ovr E PR due to SHRA/Low clds lyrs. SCT ocnl
BKN lyrs nr FL025...FL040 w/SHRA. AFT 09/15z expect incr clds
across the region with potential for additional late morning and
aftn convection in and around the islands with Psbl MVFR/ brief
IFR conditions at times mainly ovr Central Mtn range of PR. Sfc
wnds calm to LGT/VRB,bcmg ENE at 10-15 kt with occasionally higher
gusts and sea breeze variations. Brief wind gusts BTW 20-25 kts
accompanying SHRA/Isold TSRA psbl aft 09/16Z and rest of prd.

&&

.MARINE...Large swells from Major Hurricane Lee will reach the
regional waters today and will continue to do so through next week.
Seas of up to 15 feet are possible throughout this period. For
now, Small Craft Advisories are therefore in effect for the
offshore and coastal Atlantic waters and Anegada Passage. Coastal
areas, particularly along the northern and eastern shores, are at
risk of dangerous surf conditions and rip currents starting
tonight through next week. Mariners and beachgoers should exercise
caution and heed advisories.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Sun Sep 10 2023


.SYNOPSIS...

Tropical moisture will continue to be present steered by Hurricane
Lee, currently northeast of the area. Throughout the week,
external bands of this system with showers and thunderstorms,
along with gusty winds, can reach sectors of the islands. Urban
and small stream flooding is likely and local flash flooding is
possible. Marine and coastal conditions are anticipated to worsen
today and extend for most of the workweek.

&&

.SHORT TERM...Sunday through Tuesday...

For the rest of the morning...Peripheral external bands spiraling
outwards from the distant Hurricane Lee will continue to bring
isolated to scattered showers across the regional waters and local
islands steered by the prevailing northeast low level wind flow. On
the forecast track, Lee is expected to pass well north of the U.S
Virgin Islands and Puerto Rico into early next week. Overnight low
temperatures along the coastal areas will range in the upper 70s to
low 80s, and in the upper 60s to low 70s in higher elevations. No
significant rainfall accumulations are expected during the morning
hours, but brief periods of moderate to locally heavy rains may
cause ponding of water on roads along with gusty winds as the
showers pass by.

For the rest of the day, due to the current track and broad cyclonic
circulation of Lee, expect the local winds to gradually weaken as a
col area sets up across the region, thus promoting light and
variable winds. The weak steering winds along with sufficient
moisture advection, intense heating and local effects along with sea
breeze variations will promote periods of heavy rain and locally
strong thunderstorms especially along the Cordillera Central of
Puerto Rico during the afternoon hours. These expected conditions
may increase the likelihood of flooding rains during the afternoon
hours across these areas. As a result of the expected conditions,
rainfall amounts between 1 to 4 inches will be possible,
particularly in the Cordillera central, along the southern slopes,
and eastern Puerto Rico. The San Juan metro area and the USVI may
also experience periods of afternoon showers but lesser amounts and
rainfall accumulations are so far expected.

For Monday and Tuesday expect the fairly light and variable winds to
continue as Hurricane Lee is forecast to continue west northwest
across the Atlantic well north of the region. However by late Monday
into tuesday a light south to southwesterly flow is forecast as Lee
pulls northwards and away from the area. Consequently the disruption
in the overall circulation across the region is expected to continue
with recent model guidance all suggesting a gradual increase in
moisture content as Lee lifts further north and pulls a trailing
moisture plume across the region while the local winds become more
southwesterly by Tuesday.

During the period, also expect hot and humid conditions to persist
with temperatures expected to soar in the low to mid 90s along some
coastal and urban areas with maximum heat indices possible reaching
excessive Heat warning and Heat advisory conditions.

That said, expected sufficient moisture transport and pooling across
the region each day for early morning and afternoon convection
across the islands and coastal waters. Some of this activity will be
locally heavy at times and may cause urban and small stream flooding
as well as ponding of water on roads and in poor drainage areas.
Mudslide will remain possible in areas of steep terrain especially
areas that have experienced periods of heavy rains in recent days.
Marine and coastal surf zone conditions will continue to rapidly
deteriorate as Hurricane Lee moves north of the region. These
hazardous and dangerous marine conditions are expected to last over
much of the upcoming week.

Please continue to to stay informed with the latest advisories and
updates from the National Hurricane Center and our local forecast
office WFO San Juan PR, and regarding the marine and coastal
conditions over the next several days.

&&

.LONG TERM...Wednesday through Sunday...

Anticipate a wet and unstable weather pattern for the long-term
period as the feeder bands from Hurricane Lee are set to maintain
their influence over the region.

As of the latest information from the National Hurricane Center
(NHC), the core of Hurricane Lee will be positioned over 400 miles
to the west-northwest of Puerto Rico by Wednesday. Nonetheless, the
impact of Lee will extend to the nearby islands, carrying the possibility
of notable weather effects. The latest guidance indicates that Lee's
feeder bands will interact with an approaching Tropical Upper-
Tropospheric Trough or TUTT Low from the northeast, leading to the
likelihood of active weather conditions by the second half of the
week. Models have maintained consistency across successive cycles
of this weather pattern. Therefore, POPs have been raised during
this time frame to accurately depict this scenario.

Should this interaction unfold as presently forecasted, the likelihood
of flooding risk will escalate with the heaviest downpours. This
is due to the combination of moisture from Lee's feeder bands and
the instability associated with the TUTT. This may result in the
risk of flash flooding and localized flooding in vulnerable areas.
Light southerly winds induced by Lee could enhance rainfall
accumulations and increase the potential of flooding risk across
the San Juan metro area. Some areas could experience gusty winds
associated with the strongest thunderstorms, potentially causing
isolated power outages and minor wind damage. Lingering effects
will spread to the weekend as well, although with a gradual
improvement in weather conditions.

It is crucial to emphasize that the timing and intensity of this
interaction between Lee's feeder bands and the TUTT remain highly
uncertain. As this scenario is expected late in the forecast period,
significant changes in the forecast of either feature could alter
the potential impacts.

The first half of the forecast period will likely experience hot
weather conditions, primarily due to prevailing light southerly
winds and elevated moisture levels. These factors will combine to
increase heat index values, making for uncomfortable conditions
across the region. However, we anticipate improving conditions by
the weekend as easterly winds bring relief from the heat. Continue
to monitor local forecasts for updates and any advisories that
may be issued.

&&

.AVIATION...
VFR conds will prevail at all terminals. However, the external bands
from Hurricane Lee located (AT 03Z) near 21.0N...59.9W and about 285
MI...NE of the Northern Leeward Islands, will bring occasional SHRA/
Isold TSRA to the regional waters and TJSJ/TJBQ/TIST/TISX til 10/13Z.
Thereafter, SHRA/Isold TSRA expected to develop mainly across the
Central Mtn range of PR fm 10/16z-23z. This will create MTN Top
obscr and brief MVFR/Limited IFR conds with SHRA/TSRA. BKN ocnl OVC
cig nr FL025...FL040 psbl during prd with Isold to SCT SHRA en route
btw PR and the USVI. SFC winds will be calm to light and variable,
bcmg light fm the northeast to north around 10 kt aft 10/14z with
sea breeze variations.

&&

.MARINE...Marine and coastal conditions will deteriorate from today
onward. The breaking waves will increase to 10 feet or more today
across the north and east-facing beaches in St Croix and will spread
into the Atlantic Coastline of Puerto Rico tonight through this
week. The swell will peak Monday through Wednesday when seas between
10 and 15 feet are forecast, especially for the Atlantic and eastern
waters. The breaking waves will also peak between 15-20 feet Monday
into Wednesday. Coastal flooding may affect the most vulnerable
areas along the Atlantic Coastline of Puerto Rico and the eastern
half of St Croix.

&&

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
509 AM AST Mon Sep 11 2023

...New SYNOPSIS, AVIATION, MARINE...

.SYNOPSIS...
AT 09Z UTC...Hurricane Lee centered near 23.1N 62.6W. Minimum
central pressure at 950HPA and was moving to the northwest or 310
degrees at 7 mph/6 kts. Maximum sustained winds 120 mph/105 kts.
Please continue to follow the National Hurricane Center (NHC) for
latest guidance for additional track and intensity forecast.

Occasional bands of moisture steered by the broad circulation of
Hurricane Lee, will continue to spiral south and west across the
region bringing intervals of showers and thunderstorms, along with
brief wind gusts over the local waters and mainly coastal sectors of
the islands during the rest of the early morning hours. Intense
daytime heating and the fairly light north northwesterly winds,a
long with good sea breeze variations will favor afternoon convection,
mainly over portions of the central interior, the east interior
and San Juan metro, then around the U.S. Virgin islands later in
the afternoon.

.Impacts...Urban and small stream flooding will be likely with local
flash flooding possible in isolated areas over Puerto Rico. Marine
and coastal conditions are forecast to deteriorate throughout the
day as Lee tracks northwest and moves north of the region. Hazardous
marine and dangerous surf zone conditions along with life-threatening
rip currents will therefore affect the islands for the next several
days. Hot and humid conditions will persist with high temperatures
forecast to reach the low to mid 90s along coastal and urban areas
with maximum heat indices reaching excessive Heat advisory conditions
in some areas.

&&

.SHORT TERM...Today through Wednesday
Variable weather conditions prevailed across the region during
the overnight hours. The radar Doppler showed some brief isolated
to numerous showers moved across the north coastal areas due to
the northeastern wind flow generated by Hurricane Lee at almost
350 miles northeast of the region. The bulk of the shower remained
over the waters, and rainfall accumulations were insignificant.
Overnight temperatures were in the upper 70s to the lower 80s
across the coastal areas, between the low to mid-70s in the
mountains, and even lower in valleys.

Variable weather conditions will persist during the short-term
period due to Hurricane Lee moving northwestward north of the
region. For today, relatively light to variable winds will continue,
shifting more from the south-southwest in response to the northwest
movement of Hurricane Lee. Given this change in the wind pattern,
the shower's focus will be more over the interior, moving into the
northeastern section near the San Juan metro area. According to the
GOES, Satellite Imagery derived the PWAT across the area round
between 1.7 to 2 inches, which remains above the climatological
thresholds. Therefore, the forecast for today calls for afternoon
convection across the interior and northeastern sections with a
moderate risk of a flood threat.

On Tuesday, as Hurricane Lee will lift northward, the south-
southwesterly will prevail across the islands. Model guidance
suggests moisture intrusion for most of the day, but the satellite
imagery shows a slot of less moisture. This area will move in by
Tuesday, limiting somewhat the amount of shower activity. Although
there is a lack of moisture, the shower activity that develops will
be localized over the interior and northern by Tuesday afternoon.
More moisture will move in by Wednesday, increasing the frequency of
the shower activity across the region. For Thursday, winds will
drift more from the south, and according to The Gálvez-Davison Index
(GDI), isolated to scattered thunderstorms will develop over the
windward sections.&&

.LONG TERM...Thursday through Monday...
Anticipate a continued moist and unstable weather pattern to continue
at least through Thursday as some lingering feeder bands from Hurricane
Lee may still lift up across the region steered by a southerly wind
flow influenced by its broad cyclonic circulation.

The latest model guidance although reflecting some discrepancies in
the lingering effects of Lee's trailing feeder bands both suggest a
deepening Tropical Upper-Tropospheric Trough (TUTT) north and
northeast of the region, thus resulting in unstable condition aloft
by the latter part of the period. Consequently the potential for
early morning and afternoon convection will remain likely each day
with a good change of enhanced afternoon thunderstorm activity
especially across the central interior and northern half of Puerto
Rico.

If this overall pattern continues to unfold, the likelihood of urban
and flash flooding risk will be high with the heavy rains during each
afternoon due to the combination of lingering moisture from Lee's
feeder bands and the instability aloft associated with the TUTT. A
slow but gradual improvement is expected by the latter part of the
upcoming weekend into Monday.

Overall there still remain some uncertainty in the timing and coverage
of the convective activity associated with the lingering moisture
field and the presence of the upper trough. Therefore further adjustments
may be made for the latter part of the forecast period due to any changes
in the overall scenario and potential impacts. Please continue to monitor
local forecasts for updates and any advisories that may be issued.

&&

.AVIATION...
VFR conditions will prevail for most of the TAF sites; however,
ISO to SCT showers with TSRA near TJSJ will briefly result in MVFR
conditions at 11/17Z & TJPS will mainly see VCSH around
11/18-11/22Z. Winds will remain calm to light and VRB and shift
from the south to southwest at 5 to 10 kt after 11/13z with sea
breeze variations and higher gusty winds near the showers. &&

&&

.MARINE...The northerly swell will continue deteriorate marine
and coastal conditions today through at least mid-week. The swell
will peak today through Wednesday, when seas between 10 and 15 feet
are possible, especially for the Atlantic and eastern waters. Isolated
minor coastal flooding may affect the most vulnerable areas along the
Atlantic Coastline of Puerto Rico and the eastern half of St Croix.
Please refer to the latest Marine Weather Message (MWWSJU) and
Coastal Hazard Message (CFWSJU) and Coastal Water Forecast
(CWFSJU) issued by WFO San Juan PR for additional info and
updates.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
536 AM AST Tue Sep 12 2023

...New SYNOPSIS, AVIATION, MARINE...

.SYNOPSIS...
A moist southwesterly wind flow continued across the region
overnight and into the morning ours bringing periods of showers
and isolated thunderstorms to portions of the islands and coastal
waters. Although somewhat drier conditions are expected today,
there will be sufficient moisture transport from the distant
Hurricane Lee's feeder bands, to support afternoon showers and
thunderstorm development. The showers and thunderstorm development
should be focused mainly along the central interior and east
sections of Puerto Rico, including around the San Juan metro and
and mainly around the northern U.S Virgin Islands. &&

.SHORT TERM...Today through Thursday

Variable weather conditions prevailed across the region during the
overnight hours. The radar Doppler showed some brief isolated to
scattered showers moved across the northwestern area, affecting the
coastal regions and some municipalities across the northwestern and
the south-central sections of Puerto Rico through Thursday

Variable weather conditions prevailed across the region during the
overnight hours. The radar Doppler showed some brief isolated to
scattered showers moved across the northwestern area, affecting the
coastal regions and some municipalities across the northwestern and
the south-central sections of Puerto Rico. The bulk of the showers
were observed in Aguadilla and Las Marías, but rainfall
accumulations were less than one inch. Overnight temperatures were
in the upper 70s to the lower 80s across the coastal areas, between
the low to mid-70s in the mountains, and even lower in valleys.

Today, a variable weather pattern will prevail across the region due
to Hurricane Lee, located more than 350 miles northeast of the area.
Lee will continue to aid the southwesterly component in winds,
drifting all the morning activity across the northwestern and
southern sections. Although high cloudiness will be present, the
southwesterly wind, the good amount of clear to partly cloudy skies,
will enhance heat indices between 108 to 111 across Mayaguez and
vicinity, from Aguadilla to Arecibo, the northeastern PR, Culebra,
Vieques, and St. Croix, where a Heat Advisory will be in effect from
10 AM to 5 PM. Across the northcentral, heat indices will reach even
more, reaching or exceeding 114 degrees, where an Excessive Heat
Warning is in effect from 10 AM AST to 5 PM AST. The available
moisture, the diurnal heating, and the local effects will favor
another active afternoon across the interior and northeastern PR.
The heaviest activity could result in water ponding in roadways and
some urban flooding across localized areas.

On Wednesday into Thursday, as Hurricane Lee lifts even northward, a
more south component in winds will prevail across the islands. So
far today, model guidance suggests less moisture intrusion for the
morning hours, increasing during the day to PWAT values in the
climatological normals. Therefore, atmosphere conditions will be
favorable for shower activity. The heaviest activity would result in
isolated thunderstorms, as The Gálvez-Davison Index (GDI) suggested.
Therefore, the forecast includes variable morning conditions,
followed by the afternoon convection across the southern interior
and norther sections.to Rico. The bulk of the showers
were observed in Aguadilla and Las Marías, but rainfall
accumulations were less than one inch. Overnight temperatures were
in the upper 70s to the lower 80s across the coastal areas, between
the low to mid-70s in the mountains, and even lower in valleys.

Today, a variable weather pattern will prevail across the region due
to Hurricane Lee, located more than 350 miles northeast of the area.
Lee will continue to aid the southwesterly component in winds,
drifting all the morning activity across the northwestern and
southern sections. Although high cloudiness will be present, the
southwesterly wind, the good amount of clear to partly cloudy skies,
will enhance heat indices between 108 to 111 across Mayaguez and
vicinity, from Aguadilla to Arecibo, the northeastern PR, Culebra,
Vieques, and St. Croix, where a Heat Advisory will be in effect from
10 AM to 5 PM. Across the northcentral, heat indices will reach even
more, reaching or exceeding 114 degrees, where an Excessive Heat
Warning is in effect from 10 AM AST to 5 PM AST. The available
moisture, the diurnal heating, and the local effects will favor
another active afternoon across the interior and northeastern PR.
The heaviest activity could result in water ponding in roadways and
some urban flooding across localized areas.

On Wednesday into Thursday, as Hurricane Lee lifts even northward, a
more south component in winds will prevail across the islands. So
far today, model guidance suggests less moisture intrusion for the
morning hours, increasing during the day to PWAT values in the
climatological normals. Therefore, atmosphere conditions will be
favorable for shower activity. The heaviest activity would result in
isolated thunderstorms, as The Gálvez-Davison Index (GDI) suggested.
Therefore, the forecast includes variable morning conditions,
followed by the afternoon convection across the southern interior
and northern sections.

&&

.LONG TERM...Friday through Tuesday...

The latest model guidance still suggests lingering effects of
Lee's trailing feeder bands across the region through Friday along
with a deepening Tropical Upper-Tropospheric Trough (TUTT) north
and northeast of the region. This along with the expected southeasterly
wind flow will result in unstable conditions and support good afternoon
convection especially across portion of the central and north sections
of Puerto Ric. Expect late evening and morning showers to affect the
U.S. Virgin islands and also sections of eastern Puerto Rico.

For the weekend and at least into Monday, a gradual erosion of moisture
is expected as winds become more east northeast and a mid to upper
level ridge builds across the region. This will therefore increase
stability aloft and favor a more typical summertime weather pattern.
Consequently the potential for early morning and afternoon convection
will remain possible but with still a good chance of enhanced afternoon
thunderstorm activity due to good daytime heating and local effects,
steered by the local wind flow. By Tuesday there remain a lot of uncertainty
in the forecast, as model guidance suggest the approach of another
strong tropical wave or area of Low pressure northeast of the region.
There however remains a lot of inconsistencies in the models and will
therefore continue to monitor the next few model run to see how this
unfolds.

As far as impacts for the period, there will be moderate risk for
urban and flash flooding each day due to periods of locally heavy
rains each afternoon, mainly due to the combination of lingering
moisture and good daytime heating.

&&

.AVIATION...
VFR conditions will prevail for most of the TAF sites.However,
VCSH showers will prevail near TJBQ until 12/15Z. Afternoon
showers across the interior and northern sections could be
lowering the ceiling near TJBQ, TJSJ & TJPS around 12/15Z to
12/19Z. Light winds will persist from the west until 12/18Z,
becoming more from the south with sea and land breeze variations.

&&

.MARINE...
Northerly swell action generated from Hurricane Lee will continue
to invade and batter the Atlantic Coastline with wave heights between
4 and 7 feet with a wave period of 11 and 13 seconds, breaking waves
between 8 and 13 feet still expected across the north and east-facing
beaches in Puerto Rico and the U.S. Virgin Islands. Hazardous seas
and dangerous rip current conditions will continue for the next several
days. Refer to the Coastal Hazard Message (CFWSJU) and Marine Weather
Message (MWWSJU) for additional information.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
557 AM AST Fri Sep 15 2023


.SYNOPSIS...

Once again, expect the hot conditions to prevail today. However,
afternoon convection is still possible. Surface winds will become
easterly by Saturday, ending the trend of southerly wind flow.
High heat index values are likely each day. Northerly swell from
Hurricane Lee will continue to dissipate across the local waters
and northern exposed coastlines.

&&

.SHORT TERM...Today through Sunday...

At the surface, the effects of Hurricane Lee are fading for the
local area, but some subsidence is still found above the marine
layer that has been suppressing shower activity overnight even
though precipitable water values in the 15/00Z radiosonde run were
slightly better than 2 inches. High pressure is now found between
Hurricane Lee over 1100 miles north of Mona Island and a low
pressure (AL97) near 14 north and 43 west or 1200 miles east of the
eastern most Windward Islands in the tropical Atlantic. This high
pressure is ridging into the northeastern Caribbean. AL97 will
likely be a tropical storm when it crosses 20 north near 50 west
early Sunday morning, but we will remain nominally under the
influence of the high pressure and east northeast-to-east winds
during the short-term period. Precipitable water values will
continue to decrease through Sunday with an intervening dry slot
late on Saturday afternoon. This will be particularly true on Sunday
when mid-level layers also dry significantly. Hence, most of the
rain and thunderstorms during the period will be due to local
effects in southeast winds on Friday and more easterly winds on
Saturday and Sunday.

Temperatures have remained very warm in most areas. San Juan tied
its warmest maximum and average temperature for the date yesterday
and broke its overnight minimum record since records began in 1899.
Although temperatures are expected to come down around 2 or 3
degrees today, it will still be very warm with high humidity values
in the lower elevations of the north and east portions of Puerto
Rico. Therefore, an excessive heat warning has been issued for north
central Puerto Rico, San Juan and vicinity as well as for Culebra
and Vieques. Heat advisories also exist for other lower elevation
zones including Saint Croix, and eastern and northwestern Puerto
Rico.

These warm conditions and weaker moisture will keep conditions hot
with showers and isolated thunderstorms in some areas of western and
interior Puerto Rico and the U.S. Virgin Islands.

At upper levels high pressure wedged between Hurricane Lee and a
TUTT low near 25 north and 55 west will keep winds light and
generally north or northeast. Some divergence aloft and temperatures
cooling a little over a degree at 500 mb will provide a little help
through tonight for thunderstorms both over the local waters and
during the afternoon in the interior and west, where heat and
moisture are abundant.

&&

.LONG TERM...Monday through Thursday...

The main concerns for this part of the forecast are the constant
changes in wind direction, and the increase in moisture content
across Puerto Rico and the U.S. Virgin Islands as a tropical wave
now monitored by the National Hurricane Center continues to move
way north of the forecast area. At this time, the latest model
guidance suggests a gradual increase in moisture content since
Monday. PWAT values indicate values around normal climatological
levels and near above-normal climatological moisture content by
the beginning of the workweek. However, the GFS and ECMWF cross-
section models show most moisture content below 700mb through the
period, meaning that most of the rainfall activity across Puerto
Rico and the U.S. Virgin Islands will be driven primarily by the
local effects. Currently, we anticipate easterly winds to prevail
on Monday. However, by Tuesday, winds will turn northeasterly, and
by late mid-week, they will become north along the northern areas
of the island and southerly along the southern sections. Therefore,
Wednesday afternoon activity should focus mainly on the Cordillera
Central of Puerto Rico. By the end of the period, expect mainly
variable winds across the islands. Overall, winds in the long-term
forecast should be light. Therefore, we foresee low to moderate
risk for urban and flash flooding, mainly in isolated areas each
day due to periods of locally heavy rains each afternoon. This
part of the forecast generally leans into a more humid and hot
pattern over the tropical islands, where variable weather
conditions will prevail.

&&

.AVIATION...VFR conditions will prevail thru arnd 15/15Z. Aft
15/15Z SHRA/TSRA are expected to dvlp over interior PR with mtn
obscurations and lcl MVFR-LIFR conds. MVFR conds may affect
TJMZ/TJBQ/TJSJ briefly but should not prevail. Sfc winds less than 7
kt bcmg S-SW and incrg to 10-15 kt with hir gusts in sea breezes and
nr TSRA. Max winds blo FL440 VRB less than 20 kt. Maximum wind NE 35-
45 kt btwn FL480-540.

&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated persistent wave heights
between 5-8 feet for buoys with north and western exposure and
1-3 feet for more protected buoys (Ponce, Vieques, and Saint
Thomas). The swell produced by Hurricane Lee will continue to
dissipate. For details, refer to the Marine Weather Message
(MWWSJU) and Coastal Hazard Message (CFWSJU) issued by the
National Weather Service, San Juan office.

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
533 AM AST Sat Sep 16 2023

.SYNOPSIS...
Issued at 455 AM AST Sat Sep 16 2023

The influences of post tropical Cyclone Lee are now diminishing,
but a long trailing line of convergence still remains poised just
north of Puerto Rico and the U.S. Virgin Islands and will bring
showers typical of the east northeast to east flow that we will
experience through much of the rest of next week. Temperatures
will also moderate considerably, but may still remain slightly
above normal. Showers and thunderstorms are possible each day and
at this time, and with the lighter winds, some of the rain
accumulations may lead to ponding or urban and small stream
flooding in the week ahead.


&&

.SHORT TERM...Today through Monday...

Overnight, mostly clear skies prevailed over Puerto Rico, Vieques,
and Culebra. Nonetheless, primarily variably cloudy conditions
predominated over the U.S. Virgin Islands as some showers filtered
in. The minimum temperatures along the coastal areas of PR and
the USVI fluctuated in the upper 70s to low 80s, while in the
higher mountains, they stayed in the 60s. During the night, the
wind flow across the islands was mostly land breezes. However,
some easterly components were seen.

Today, the hot and variable weather conditions will prevail across
Puerto Rico and the U.S. Virgin Islands. Daily maximum temperatures
along the coasts should fluctuate in the upper 80s to mid 90s, while
in the mountains, they will range in the upper 70s to low 80s. The
warm temperatures will be accompanied by heat indices above 108 and
112 degrees Fahrenheit in the low areas of the islands. An Excessive
Heat Warning was issued for north-central PR, Culebra, and Vieques
due to expected heat indices above 112 degrees. A Heat Advisory was
issued for northwestern and northeastern PR and St. Croix. In the
morning, we anticipate periods of isolated to scattered showers to
move across the islands. Nonetheless, in the afternoon, expect most
of the rainfall activity to focus on the interior, western, and
southwestern sections of Puerto Rico as east-northeasterly winds
prevail. At this time, models continue to suggest a weak ridge
building across the Caribbean. This weather feature will limit the
heavy rainfall to the afternoon hours, where the diurnal heating,
orographic lifting, and sea breeze effects will contribute to
thunderstorm development. Like in previous days, expect frequent
lightning and gusty winds across the affected areas. The latest
guidance suggests precipitable water content around normal to
slightly above normal climatology today. However, expect PWAT values
to fluctuate around average to below average by late Saturday into
Sunday. On Monday, similar weather conditions should prevail.
Tropical Depression number 15 was located about 1070 miles east of
the Lesser Antilles at 5 AM AST and is expected to develop into a
tropical storm later today and a hurricane by Monday.

&&

.LONG TERM...Tuesday through Friday...

Tropical depression number 15 is expected to be a hurricane by
early Tuesday morning and almost 900 miles northeast of Culebra.
This will place the col between the weak trough over the Leeward
Islands and the tropical cyclone. Hence winds across the local
area will be outside the general influence of the wind field
surrounding the hurricane and local winds will be generally east
northeast and gentle with sea breezes. Moisture will be near
normal with patches and bands of moisture being advected out of
the system toward the area that will generate showers and
thunderstorms--some with heavy rain. Currently the heavier rains
are expected on Thursday afternoon but heavy rain is likely each
afternoon in mostly interior locations. At upper levels a ridge of
high pressure is expected to hold over the area Tuesday through
Thursday and then drift westward. Currently we expect somewhat
above normal temperature through the long term period that will be
moderated by shower activity and vary only a little from day-to-
day.

&&

.AVIATION...
(06Z TAFS)
Issued at 455 AM AST Sat Sep 16 2023

VFR conditions will prevail across all terminals. Aft
16/17Z SHRA/TSRA are expected to dvlp over interior, western, and
southwestern PR with mtn obscurations and brief MVFR conds. MVFR
conditions may affect TJMZ/TJBQ briefly but should not prevail. Sfc
winds less than 6 kt bcmg E-NE and incrg to 10-15 kt with hir gusts
in sea breezes and near TSRA.

&&

.MARINE...
Issued at 455 AM AST Sat Sep 16 2023

Swell from post tropical cyclone Lee are slowly subsiding, but
will linger well into the upcoming week. Swell from the Hurricane
anticipated to pass well northeast of the area by some 900 miles
will begin to arrive on Wednesday when small craft advisories are
likely to be required.