Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Sat May 17 2025

.KEY MESSAGES...

* A strong upper-level trough will maintain an unsettled weather
pattern, heightening the risk of excessive rainfall across
Puerto Rico and the U.S. Virgin Islands today and possibly tomorrow.

* Saharan dust will continue to move across the region, resulting
in hazy skies through at least next Tuesday.

* Afternoon showers and thunderstorms, driven by local effects and
daytime heating, are expected to develop daily next week across
the interior and western Puerto Rico.

* Decreasing winds will promote low rip current risk across all
coastal areas of the islands throughout the weekend.

&&

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

Radar and satellite analysis indicated mostly quiet weather across
Puerto Rico overnight, with areas of fog developing over the
mountainous interior. Since 8 PM AST, scattered showers and isolated
thunderstorms affected eastern Puerto Rico—including Vieques and
Culebra—as well as the U.S. Virgin Islands, resulting in increased
cloud cover and peak radar-estimated rainfall totals of 1 to 2
inches in Fajardo and Saint John. Winds were generally light, with
measurable speeds below 10 mph mainly observed across windward
coastal areas. Minimum temperatures dropped into the lower 60s in
the higher elevations, while exposed coastal areas of southern and
eastern Puerto Rico, along with the local islands, remained in the
upper 70s.

A mid-to-upper-level cutoff low and its associated surface-induced
trough will remain the dominant weather feature through the weekend.
This pattern will continue to support deep convective development,
especially today and into early Sunday, aided by cooler-than-normal
temperatures aloft and an abundance of tropical moisture. Precipitable
water values today will range between 1.9 and 2.1 inches, near to
above typical levels for this time of year. A gradual drying trend
is anticipated beginning Sunday into early next week, as drier air
filters in behind the upper-level trough. While winds will gradually
diminish as the surface trough settles northeast of the region over
the next few days, breezy conditions may persist today around the
Anegada Passage, just east of the U.S. Virgin Islands.

Despite the presence of a Saharan Air Layer (SAL), which may locally
suppress convective activity, today is still expected to be the most
active day of the short-term period. Scattered to locally numerous
showers and isolated thunderstorms are forecast, with the greatest
impacts likely over eastern Puerto Rico, the Cordillera Central, and
northwestern Puerto Rico, including the San Juan metro area. Rains
from slow-moving showers will support a limited to elevated risk of
excessive rainfall. The strongest thunderstorms may also produce
frequent lightning, strong wind gusts, and the potential for small
hail. Given already saturated soils, urban and small stream
flooding, localized flash flooding, and landslides remain possible.

The overall pattern becomes less favorable for organized convection
by Sunday and Monday. While isolated to scattered showers and
thunderstorms will still be possible, mainly during the afternoon
hours, activity is expected to be less frequent and less intense,
with flooding threats becoming more localized. Temperatures will
remain near seasonal normals throughout the period, though a limited
excessive heat hazard may develop across northern and western Puerto
Rico on Sunday and Monday. Please refer to the Experimental
Graphical Hazardous Weather Outlook for the latest depiction of at-
risk areas.

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

The forecast remains generally on track for the long-term period.
At the surface, a high-pressure system over the Atlantic Basin
will maintain an easterly to southeasterly wind flow throughout
the forecast period. On Tuesday and Wednesday, a weak upper-level
trough will move across the area, while a mid-level ridge builds
over the western Caribbean. Winds will remain light through at
least midweek, then gradually increase from Thursday onward. According
to the latest model guidance, precipitable water values will
fluctuate around seasonal averages—approximately 1.8 inches on
Tuesday, decreasing to between 1.5 and 1.7 inches on Wednesday and
Thursday, and rising again to around 1.8 inches by Friday
afternoon onward.

Given this pattern, marginally unstable conditions are expected
mainly on Tuesday and Wednesday. The combination of moisture,
daytime heating, and local effects will favor shower development,
particularly during the afternoon hours. However, the likelihood
of thunderstorms will decrease as 500 mb temperatures rise into an
above-average range (around -4 to -5 degrees Celsius), which could
limit convective development. On the other hand, by the end of
the week, temperatures are forecast to return to around -7 degrees
Celsius at 500 mb, increasing the potential for thunderstorm activity
with afternoon convection, but less moisture and instability will
be available. From Thursday through Saturday, the upper- level
trough will shift to our east, placing its convergent side over
the region, while the mid-level ridge shifts eastward and exerts
more influence, promoting more stable atmospheric conditions.
Either way, afternoon convection cannot be ruled out due to the
available moisture (mainly confined in the lower levels of the
atmosphere) and local effects, particularly across the western
portion of Puerto Rico during peak heating hours.

Temperatures are expected to remain warmer than normal throughout the
forecast period, as suggested by 925 mb temperatures, which will
peak on Tuesday and stay above average for the rest of the week.
Also, model are still showing Saharan dust concentrations over the
region at least through Tuesday.

The main takeaway is that there will likely be rainfall activity
each day, mainly during the morning in eastern Puerto Rico and
the U.S. Virgin Islands, and during the afternoon in western
Puerto Rico. Tuesday has the highest probability of afternoon
rainfall in the west, with chances between 60% and 70%, followed
by Wednesday with 50% to 60%. From Thursday through Saturday, more
stable conditions are expected, but available moisture should
still result in afternoon convection, although it is not expected
to be deep or widespread. The flood risk will likely remain limited.

&&

.AVIATION...
(06Z TAFs)

Unsettled conditions will bring MVFR and brief IFR periods at most
TAF sites, continuing across USVI terminals through the period.
SHRA/TSRA will affect Puerto Rico terminals mainly between 17/16-
22Z. Saharan dust concentrations remain minor, with visibility above
6 miles, except near +SHRA/TSRA. Light to calm winds at first,
increasing to 8–12 mph with strong sea breeze variations after
17/14Z. Gusts possible near strong TSRA.

&&

.MARINE...

A surface trough will influence light to moderate easterly winds. A
deep trough with its axis currently located to the west of the region
will continue to support unsettled weather conditions today, with a
high chance of thunderstorm development mainly across the eastern
local waters. These storms could lead to locally higher winds and
seas. In addition, hazy conditions are likely over the next few days
due to the presence of Saharan dust.

&&

.BEACH FORECAST...

There is a low rip current risk today across all coastal areas of
the islands as winds are expected to become lighter. However,
life-threatening rip currents often occur near groins, jetties,
reefs, and piers. Similar conditions are expected to prevail over
the weekend and into early next week. A moderate rip current risk
will likely return around midweek. For more information, please
refer to the latest Coastal Hazard Message (CFWSJU) and Surf Zone
Forecast (SRFSJU).

&&

.HYDROLOGY...

Abundant tropical moisture (with heavy moisture levels) and
increased instability due to a nearby cutoff low will keep the
flood risk high across Puerto Rico and the U.S. Virgin Islands
today and tonight. Since soils are already saturated and some
rivers are running high, any additional heavy rain could cause
urban and flash flooding, river flooding, and landslides—even
after the heaviest rain stops. For more details, please see the
Hydrologic Outlook (ESFSJU).

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
517 AM AST Sun May 18 2025

.KEY MESSAGES...

* An upper-level low will maintain an unsettled weather pattern,
heightening the risk of excessive rainfall across Puerto Rico
and the U.S. Virgin Islands through today.

* The Saharan Air Layer will continue to advance across the
region, with concentrations expected to peak from this
afternoon into Monday. As a result, hazy skies will persist
through at least Tuesday or Wednesday of next week.

* Afternoon showers and thunderstorms, driven by daytime heating
and local effects, are expected to develop daily next week
across the interior and western Puerto Rico.

* Above-normal temperatures are anticipated this week, mainly next
Tuesday through the end of the week where an elevated heat risk
will be likely particularly across northern and western Puerto
Rico.

&&

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

A quiet night prevailed across Puerto Rico and the US Virgin
Islands, with mostly calm conditions and some fog developing over
the mountainous interior. Scattered showers were observed over
the surrounding waters, with some moving over the US Virgin
Islands and eastern Puerto Rico, producing limited rainfall.
Minimum temperatures ranged from around 60°F in the higher
elevations to the mid-70s in isolated areas of eastern Puerto
Rico. At the same time, the US Virgin Islands remained warmer,
with lows in the mid to upper 70s. Winds were generally light,
mostly below 10 mph, mainly along windward coastal areas.

A lingering upper-level cutoff low and its associated surface-
induced trough will remain the dominant weather feature today,
followed by a weaker upper-level trough sinking south into the
Caribbean by late Monday into Tuesday. Although overall instability
will be lower than in recent days, the pattern will continue to
support deep convective development, as 500 mb temperatures rise
above typical seasonal values (above -6 °C). As drier air filters
into the region, moisture levels will diminish and remain near
typical thresholds (around 1.6–1.8 inches of precipitable water)
over the next few days. At the surface, the trough will maintain
generally light easterly winds today and Monday, shifting to an east-
southeasterly flow by Tuesday, driven by a broad surface high over
the central North Atlantic.

Despite a Saharan Air Layer (SAL), which may locally suppress
convective activity, variable conditions are expected, with a
gradual decrease in the areal coverage and intensity of showers over
the coming days. Generally, quiet mornings give way to scattered
afternoon showers and isolated thunderstorms. Marginally unstable
conditions, combined with typical moisture levels and triggered by
local forcing, such as diurnal heating and sea breeze convergence,
could still result in a locally elevated risk of excessive rainfall
and flooding. A few thunderstorms may also produce frequent
lightning and strong wind gusts, though the potential for small hail
remains low due to the lack of sufficiently cool temperatures aloft.
The most significant impacts are expected over central to northern
and western Puerto Rico, as well as downwind from Sierra de Luquillo
and the local islands into the San Juan metropolitan area and
eastern Puerto Rico, consistent with a typical diurnal pattern.

Temperatures are expected to rise over the coming days. This warming
trend may lead to limited excessive heat hazards today, with the
potential for elevated heat risks early next week, particularly
across northern and western sections of Puerto Rico. These conditions
primarily impact individuals who are especially sensitive to high
temperatures, especially outdoors without effective cooling or
adequate hydration. For the latest depiction of areas at risk from
excessive rainfall, heat, and other hazards, refer to the
Experimental Graphical Hazardous Weather Outlook.

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

The long term will feature variable weather conditions and above-
normal temperatures. At the surface, a high-pressure system over
the Atlantic Basin will maintain an easterly to southeasterly
wind flow throughout the forecast period. A weak upper-level
trough will continue moving across the area by Wednesday, while a
mid- level ridge builds over the western Caribbean. Winds will
remain light through at least Wednesday, then gradually begin to
increase from Thursday onward. In terms of moisture content, the
latest model guidance still shows precipitable water values
fluctuating around seasonal averages—approximately 1.7 to 1.9
inches. Moisture will be mostly confined below the 700 mb level,
as drier air filters into the mid and upper levels.

The combination of moisture, daytime heating, and local effects will
favor shower development, particularly during the afternoon hours.
The 500 mb temperatures will fluctuate around -6 to -7 degrees
Celsius (average for this time of year) from Wednesday through
Saturday, which can support isolated thunderstorm activity with
afternoon convection, though upper-level instability will be more
limited from Thursday onward. From Thursday through Sunday, the
upper-level trough will shift eastward, placing its convergent
side over the region, while the mid-level ridge also shifts east
and exerts greater influence—promoting more stable atmospheric
conditions. Nevertheless, afternoon convection cannot be ruled out
due to available moisture and local effects, particularly across
the western portion of Puerto Rico during peak heating hours each
day, although it is not expected to be deep or widespread. The
flood risk will likely remain limited.

One of the main concerns during this period will likely be the
warm temperatures. Temperatures are expected to remain above normal
throughout the forecast period, as indicated by 925 mb temperatures,
which stay above average. Additionally, on Wednesday, models still
show remnants of the Saharan Air Layer across the region, although
this is expected to decrease through the remainder of the period.

The main takeaway is that warmer than normal temperatures are
anticipated and rainfall activity is likely each day—mainly
during the morning in eastern Puerto Rico and the U.S. Virgin
Islands, and afternoon convection with isolated thunderstorms
across sectors of western Puerto Rico.

&&

.AVIATION...
(06Z TAFs)

There is a chance for VCSH across all USVI terminals throughout the
period, with afternoon SHRA/TSRA potentially causing brief MVFR
conditions at most PR terminals between 18/16-22Z. Winds will begin
light to calm, then increase to 10–15 kt with sea breeze influences
after 18/14Z. Gusty winds are possible near strong TSRA.

&&

.MARINE...

A surface trough will promote light to gentle easterly winds across
most local waters over the next few days. A deep upper level low
north of the region will continue to support unsettled weather
conditions through at least today. Thunderstorms will lead to
locally higher winds and seas. In addition, hazy skies will be in
place at least through next Tuesday due to the presence of Saharan
dust particles.

&&

.BEACH FORECAST...

There is a low rip current risk today and tonight across all
coastal areas of the islands. However, life-threatening rip
currents often occur near groins, jetties, reefs, and piers.
Similar conditions are expected to prevail most of the upcoming
workweek. A moderate rip current risk will likely return by the
end of the week.

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Mon May 19 2025

.KEY MESSAGES...

* An area of suspended Saharan dust is currently moving over the
region, resulting in hazy skies, especially in areas with limited
rainfall activity.

* Another active afternoon is expected across interior and
northwestern Puerto Rico, continuing the elevated flood risk.

* Southerly winds will lead to above-normal temperatures over the
next few days. This will result in a limited to elevated heat risk
during this period, particularly in urban and coastal areas

&&

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

Radar and satellite imagery registered calm conditions during the
overnight hours across Puerto Rico and the U.S. Virgin Islands.
Persistent showers did form, but they mostly remained over the
waters of the Atlantic, Caribbean, and the Mona Passage. Some
showers moved across Vieques, leaving only minimal accumulations.
Since midnight, minimum temperatures have dropped to the low to mid-
70s across coastal areas of Puerto Rico and into the 60s across the
mountainous regions, while the U.S. Virgin Islands observed mostly
upper 70s. Light and variable winds prevailed.

Based on the latest surface analysis, a surface high-pressure system
dominates the central to eastern Atlantic. This, along with a nearby
induced surface trough, will maintain an easterly to southeasterly
wind flow across our region through the forecast period. A mid-to-
upper-level trough and its associated cut-off low will continue
shifting northeastward while gradually weakening today, followed by
another weak mid-to-upper-level trough expected to move across the
region Tuesday and Wednesday. In terms of moisture content, the
latest model guidance shows precipitable water values fluctuating
between 1.8 and 2.0 inches today and Tuesday, then between 1.7 and
1.9 inches by midweek, levels considered average to slightly above
average for this time of year.

On tap for today is an overall quiet morning, with the exception of
some showers moving across the Virgin Islands and eastern Puerto
Rico. Then, model guidance supports the development of afternoon
showers and isolated thunderstorms mainly over central, northern,
and western Puerto Rico, driven by diurnal heating and sea breeze
convergence. The flood risk for today remains between limited and
elevated, as this activity will likely lead to ponding of water on
roads and in poorly drained areas, as well as flooding in urban
zones, small streams, and washes. Additionally, hazy skies are
expected as a Saharan Air Layer continues advancing across the
region, with concentrations forecast to peak today and gradually
decrease in the coming days. Mostly fair weather is expected
overnight across the local islands, with just a few passing showers
over the eastern coastal areas of Puerto Rico and surrounding
islands.

By tomorrow and Wednesday, a similar weather pattern will prevail,
with showers and isolated thunderstorms mainly developing during the
afternoon hours, but slightly improving each day. A limited flood
threat is expected across northwestern and north-central Puerto
Rico. The main concerns during this period will be the warming trend
in the temperatures. Conditions are forecast to remain above
average, with 925 mb temperatures expected to peak on Tuesday and
Wednesday near two standard deviations above normal. The heat risk
will be elevated across coastal, urban, and low-elevation areas,
affecting most individuals sensitive to heat, especially those
without effective cooling or adequate hydration.

The main takeaway is that warmer-than-normal temperatures are
anticipated, and rainfall activity is likely each day—mainly during
the morning in eastern Puerto Rico and the U.S. Virgin Islands, and
in the afternoon across central and western Puerto Rico, with the
potential for isolated thunderstorms.

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

The long-term forecast trends have not changed significantly. At the
surface, a high-pressure system over the central Atlantic will
maintain a persistent easterly to southeasterly wind flow. This high-
pressure system is expected to strengthen, increasing the pressure
gradient over the northeastern Caribbean and, consequently, wind
speeds across the region throughout the forecast period. Warmer
temperatures will still persist, although to a lesser extent than in
previous days, as the winds now have a reduced southerly component
due to the shifting position of the surface high pressure. Still,
heat index values above 100F can be expected in urban and coastal
areas during the peak hours of the day.

At upper levels, a mid-to-upper-level ridge will move in from the
west and settle over the northeastern Caribbean, pushing an upper-
level trough eastward on Thursday. This will promote some subsidence
aloft and increase 250 mb height fields, resulting in less favorable
upper-level dynamics. However, 500 mb temperatures are expected to
remain near normal, which could still provide some atmospheric
instability if sufficient lifting is present.

Precipitable water values are expected to be near seasonal normals,
fluctuating between 1.5 and 1.8 inches, which fall within the 25th
to 75th percentile range of climatological levels. Moisture levels
will remain confined below the 700 mb level for the most part as
drier air filters into the mid-levels. Despite reduced upper-level
dynamics and overall moisture, localized convective activity is
still likely due to a combination of sufficient low-level moisture,
daytime heating, and orographic lift. Morning showers are favored
across eastern Puerto Rico and the U.S. Virgin Islands, while
afternoon convection with isolated thunderstorms is possible over
western and northwestern Puerto Rico. However, due to limited upper-
level support, this activity is not expected to be deep or
widespread. As a result, the overall flood risk will remain low,
with the potential for localized elevated risk.


&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions will prevail this morning. VCSH will remain
possible this morning mainly across USVI TAF sites. Brief periods of
MVFR conditions mainly across TJSJ and TJBQ TAF sites due to VCSH
and -RA around 19/18Z through about 19/23Z. After 18/14Z, E to SE
winds at 8 to 12 knots with sea breeze variations, becoming lighter
tonight.

&&

.MARINE...

A weakening surface trough will promote light to gentle easterly
winds across most local waters through at least Tuesday. A building
surface high pressure over the central Atlantic will bring moderate
to locally fresh easterly trades from midweek onward. For today
through Tuesday, hazy skies will persist in areas with limited shower
activity due to the presence of suspended Saharan dust.

&&

.BEACH FORECAST...

A low risk of rip currents is expected to continue through most of
the workweek. However, life-threatening rip currents can still occur
near jetties and piers.

[cycloneye]

 https://x.com/TTMetOffice/status/1924468044715159670

[cycloneye]

Area Forecast Discussion...DELAYED
National Weather Service San Juan PR
519 AM AST Tue May 20 2025

.KEY MESSAGES...

* Southerly winds will contribute to above-normal temperatures over
the next few days, with today and tomorrow expected to be the
hottest. As a result, a Heat Advisory has been issued for the
northern, western, and southern coastal areas of Puerto Rico.
Other urban and coastal areas of Puerto Rico, as well as the U.S.
Virgin Islands, are also expected to experience high heat index
values.

* Lingering suspended Saharan dust will continue to produce hazy
skies, particularly in areas experiencing limited rainfall
activity.

* Another active afternoon is expected across interior and
western/northwestern Puerto Rico, continuing the elevated flood
risk.

&&

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

Radar and satellite imagery indicated calm conditions during the
overnight hours across Puerto Rico and the U.S. Virgin Islands.
Persistent showers and a few lightning strikes did form, but they
mostly remained over the Atlantic and Caribbean waters. Since
midnight, minimum temperatures have dropped to the mid to upper 70s
across coastal areas of Puerto Rico and into the 60s in the
mountainous regions, while the U.S. Virgin Islands observed mostly
upper 70s to low 80s. Light and variable winds prevailed.

Surface high pressure across the Atlantic basin and a weak surface
trough will maintain a light southeasterly wind flow today and
tomorrow, increasing to moderate by Thursday. Aloft, a weak mid- to
upper-level trough is expected to move across the local region from
the northwest today through Wednesday, as indicated by a decreasing
trend in 250 mb heights. In terms of moisture content, the latest
model guidance shows precipitable water values fluctuating between
1.8 and 2.0 inches through Wednesday, which are considered average
to slightly above average for this time of year. By Thursday, values
are expected to range slightly lower, between 1.4 and 1.6 inches.
Therefore, model guidance suggests the development of afternoon
showers and isolated thunderstorms, mainly over central, northern,
and western Puerto Rico, driven by diurnal heating and sea breeze
convergence. As a result, the flood risk for today and Wednesday
remains between limited and elevated, as this activity will likely
lead to ponding of water on roads and in poorly drained areas, as
well as flooding in urban zones, small streams, and washes. By
Thursday, the flood risk is expected to remain limited, as showers
should be less widespread.

In addition to the rain, the main focus of the forecast is the
warmer temperatures expected today and over the coming days.
Currently, the warmest days are forecast to be today and tomorrow,
with temperatures slightly easing thereafter, as suggested by 925 mb
temperatures peaking near two standard deviations above normal
before gradually decreasing. The heat risk is elevated across
coastal, urban, and low-elevation areas, affecting most individuals
sensitive to heat—especially those without effective cooling or
adequate hydration. As a result, a Heat Advisory—the first of the
season—is in effect today from 10 AM to 5 PM AST across northern,
western, and southern municipalities of Puerto Rico. Some
recommendations are: drink plenty of fluids, stay in air-conditioned
spaces, avoid the sun, and check on relatives and neighbors. Take
extra precautions when outdoors: wear lightweight and loose-fitting
clothing, and try to limit strenuous activities to early morning or
evening hours. Take immediate action if you observe symptoms of heat
exhaustion or heat stroke.

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

The long-term forecast begins with weak ridging aloft, which will
slightly reduce upper-level instability. Nevertheless, 500 mb
temperatures will remain between -6C and -7.5C, with 700–500 mb and
850–700 mb lapse rates staying within climatological normal, or even
slightly steeper than usual. This will allow marginal instability to
persist through at least the weekend. The main limiting factor will
be moisture availability, as precipitable water values and mid-level
relative humidities fall to within seasonal normals, occasionally
dipping slightly below average. Even so, moisture levels will remain
sufficient for shower development and afternoon convection,
particularly when combined with surface heating and local effects.
However, this activity is expected to have reduced areal coverage
compared to recent days. Additionally, breezy to windy conditions
will prevail, promoting fast-moving showers that will help limit
rainfall accumulations across the area. As a result, flooding risk
will be mostly limited, with the potential for ponding of water in
roads and in poorly drained areas. Localized urban flooding cannot
be ruled out.

The pattern begins to change by early next week as another upper-
level trough exits the eastern seaboard and deepens while moving
eastward toward the northeastern Caribbean. The forecast becomes
more complex, with model guidance suggesting that this trough may
interact with an approaching tropical wave, currently located near
25W. The combination of favorable upper-level dynamics and well-
above-normal tropical moisture could result in an elevated risk of
flooding. However, confidence in this scenario remains low, as it
lies near the end of the long-term forecast period. Changes in the
synoptic pattern over the coming days may affect the timing or
location of the area where these features converge. Therefore,
continue to monitor forecast updates closely as we move into early
next week.


&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions will prevail this morning. VCSH will remain
possible this morning mainly across USVI TAF sites. Brief periods of
MVFR conditions mainly across TJSJ and TJBQ TAF sites due to VCTS and
-RA around after 16Z through about 22Z-23Z. Calm winds, becoming, E
to SE winds at 8 to 10 knots after 13-14Z, Sea breeze variation
during the early afternoon, then light/ variable overnight.

&&

.MARINE...

Light to gentle easterly winds will persist across most local waters
through at least Wednesday. A building surface high pressure over
the central Atlantic will bring moderate to locally fresh easterly
trades from midweek onward. Hazy skies will persist through at least
today in areas with limited shower activity due to the presence of
suspended Saharan dust. Isolated thunderstorms will continue to
develop across the regional waters, particularly across western
coastal waters of Puerto Rico each afternoon.

&&

.BEACH FORECAST...

A low risk of rip currents is expected to continue through most of
the workweek. However, life-threatening rip currents can still occur
near jetties and piers.

&&

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
505 AM AST Wed May 21 2025

.KEY MESSAGES...

* Another day with a Heat Advisory in effect for the northern,
western, and southern coastal areas of Puerto Rico. Elevated heat
index values are also expected across other urban and coastal
areas of Puerto Rico, as well as the U.S. Virgin Islands.

* Lingering suspended Saharan dust will continue to cause hazy skies
today, though it has been diminishing and is expected to gradually
clear over the coming days.

* Another active afternoon is expected across interior and western
Puerto Rico, maintaining an elevated flood risk. However, areal
coverage and expected flooding risk are forecast to gradually
diminish in the coming days.

&&

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

Radar and satellite imagery indicated calm conditions during the
overnight hours across Puerto Rico and the U.S. Virgin Islands.
Persistent showers and a few lightning strikes did form, but they
mostly remained over the Atlantic and Caribbean waters. Since
midnight, minimum temperatures have dropped to the mid to upper 70s
across coastal areas of Puerto Rico and into the 60s in the
mountainous regions, while the U.S. Virgin Islands observed mostly
upper 70s to low 80s. Light and variable winds prevailed.

Surface high pressure across the Atlantic basin and a weak surface
trough will maintain a light southeasterly wind flow today and
tomorrow, increasing to moderate by Thursday. Aloft, a weak mid- to
upper-level trough is expected to move across the local region from
the northwest today through Wednesday, as indicated by a decreasing
trend in 250 mb heights. In terms of moisture content, the latest
model guidance shows precipitable water values fluctuating between
1.8 and 2.0 inches through Wednesday, which are considered average
to slightly above average for this time of year. By Thursday, values
are expected to range slightly lower, between 1.4 and 1.6 inches.
Therefore, model guidance suggests the development of afternoon
showers and isolated thunderstorms, mainly over central, northern,
and western Puerto Rico, driven by diurnal heating and sea breeze
convergence. As a result, the flood risk for today and Wednesday
remains between limited and elevated, as this activity will likely
lead to ponding of water on roads and in poorly drained areas, as
well as flooding in urban zones, small streams, and washes. By
Thursday, the flood risk is expected to remain limited, as showers
should be less widespread.

In addition to the rain, the main focus of the forecast is the
warmer temperatures expected today and over the coming days.
Currently, the warmest days are forecast to be today and tomorrow,
with temperatures slightly easing thereafter, as suggested by 925 mb
temperatures peaking near two standard deviations above normal
before gradually decreasing. The heat risk is elevated across
coastal, urban, and low-elevation areas, affecting most individuals
sensitive to heat—especially those without effective cooling or
adequate hydration. As a result, a Heat Advisory—the first of the
season—is in effect today from 10 AM to 5 PM AST across northern,
western, and southern municipalities of Puerto Rico. Some
recommendations are: drink plenty of fluids, stay in air-conditioned
spaces, avoid the sun, and check on relatives and neighbors. Take
extra precautions when outdoors: wear lightweight and loose-fitting
clothing, and try to limit strenuous activities to early morning or
evening hours. Take immediate action if you observe symptoms of heat
exhaustion or heat stroke.

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

The weekend will begin with a typical seasonal weather pattern, as
near-normal to slightly below-normal moisture levels combine with
marginal instability aloft, associated with weak ridging over the
northeastern Caribbean. Shower activity will follow the
characteristic diurnal pattern, with passing showers affecting
windward coastal areas of the islands during the night and early
morning hours. This will be followed by afternoon convective
activity, driven by surface heating, sea breeze convergence, and
orographic lifting over the interior and western portions of Puerto
Rico.

A few isolated thunderstorms may develop at times during this
period, but they are expected to be brief. Additionally, breezy
conditions will result in fast-moving showers, limiting rainfall
accumulations in any specific area. At most, a limited flooding risk
is expected, potentially leading to ponding on roadways and poor
drainage areas, with very localized urban and small stream flooding.
A limited excessive heat risk will also persist through the weekend
across urban and coastal areas, primarily affecting heat-sensitive
individuals, especially those outdoors without effective cooling or
adequate hydration.

Uncertainty persists by early next week due to the interaction
between a deepening upper-level trough to the west of the forecast
area and an approaching tropical wave from the east, currently
located near 28.5W. The timing and placement of these synoptic
features remain fairly consistent across model guidance, with the
latest runs positioning the trough axis over Hispaniola between
Tuesday and Wednesday. This places our area on the favorable
(eastern) side of the trough. At the same time, the tropical wave is
expected to begin lifting northward, moving over or near our region.
However, the most active portion of the wave now appears to be
slightly farther west compared to previous model runs. Despite this
shift, well above-normal moisture and increased instability aloft
will be present across the forecast area, increasing the potential
for numerous showers and thunderstorms. This could lead to an
increased flooding threat for Puerto Rico and the U.S. Virgin
Islands.

However, the Caribbean may be under the influence of the suppressing
phase of the MJO, which is indicative of reduced upper-level
divergence and decreased favorability for deep convective activity.
In fact, the latest CPC Global Tropics Hazards Outlook assigns a 50%
to 65% probability of below-average rainfall across the northeastern
Caribbean. This introduces additional complexity to the forecast.
Nevertheless, it is important to continue monitoring the situation,
as there remains a chance for increased moisture convergence and
instability to result in a heightened flooding risk by early next
week.


&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions will prevail during this forecast period.
Brief VCSH is expected across eastern TAF sites this morning.
Periods of MVFR conditions are possible at TJSJ and TJBQ due to VCTS
and -RA between 16Z and approximately 21–22Z. Winds will be calm in
the morning, becoming east to southeast at 8–10 knots after 13–14Z,
with sea breeze variations in the early afternoon, then light and
variable overnight.

&&

.MARINE...

Light to gentle easterly winds continue today across most local
waters. However, a building surface high pressure over the central
Atlantic will bring moderate to locally fresh easterly trades tonight
through the weekend. Isolated thunderstorms will continue to develop
across the regional waters, particularly across the northern and
western coastal waters of Puerto Rico each afternoon.

&&

.BEACH FORECAST...

Weak winds over the area continue to result in tranquil seas and,
consequently, a low risk of rip currents. However, life-threatening
rip currents can still occur near jetties and piers.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
512 AM AST Thu May 22 2025

.KEY MESSAGES...

* Afternoon showers and thunderstorms are expected daily across
the Cordillera Central of Puerto Rico, creating a limited to
elevated risk of flooding rains.

* The warm to hot period will continue today, gradually improving
tomorrow into the weekend.

* An unstable weather pattern may return by the beginning of the
workweek.

&&

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

Calm weather conditions prevailed overnight, with land breezes
observed in most coastal areas. Overnight minimum temperatures
dropped to the mid to upper 70s along the coast and to around the
mid-60s in the mountains.

Another above-normal temperature day is expected today, although to
a lesser extent than in recent days. The 22/06Z 925 mb temperature
data from NUCAPS showed values ranging from 20.7C to 21.7C across
the forecast area, about 1 to 2 degrees Celsius higher than what
model guidance indicated for that time. A similar pattern was noted
in the 22/00Z TJSJ upper-air sounding, which showed 925 mb
temperatures about 1 degree warmer than model forecasts. All
observed values remain well above the climatological normal for this
time of year. Moisture levels will be slightly lower compared to
recent days, which may lessen the impact on heat index values.
However, with the warming trend persisting and sufficient moisture
still present, a Heat Advisory has been issued, this time limited to
the northern and western municipalities of Puerto Rico. Residents
are advised to limit strenuous outdoor activities to the early
morning or evening hours and to stay well-hydrated throughout the
day. A gradual decrease in temperatures is expected over the coming
days.

Today and through the short-term forecast period, a slight shift in
the weather pattern is expected. The upper-level trough that has
been influencing the northeastern Caribbean will continue to move
eastward. In its wake, weak ridging aloft will build over the
forecast area, accompanied by a gradual increase in 250 mb heights.
However, marginal instability will persist, especially today, as the
upper-level trough remains nearby. Instability indicators, such as
500 mb temperatures and low- to mid-level lapse rates, will remain
at near normal levels.

As mentioned earlier, a slightly drier slot, as observed by GOES-19
Precipitable Water satellite data, is expected to move in during the
morning hours. However, an east-southeast wind flow will help return
moisture levels to near normal by this afternoon, with those
conditions expected to persist through the rest of the short-term
period. Steering winds will strengthen today as a surface high
pressure over the central Atlantic builds, increasing the pressure
gradient over the northern Caribbean through the weekend. Shower and
thunderstorm activity will follow a typical seasonal pattern, with
some showers developing over local waters during the night and early
morning, occasionally moving over windward coastal areas.

During the afternoon, marginal instability combined with sufficient
moisture, surface heating, sea breeze convergence, and orographic
lifting will support the development of showers and isolated
thunderstorms over the interior and western portions of Puerto Rico.
The highest rainfall accumulations are expected this afternoon, as
today will feature the greatest instability due to the proximity of
the upper-level trough and slower steering winds. This could lead to
an elevated flooding risk in very localized areas out west. On
Friday and Saturday, rainfall accumulations during the afternoon are
expected to decrease due to faster-moving showers and the trough
shifting farther away. Nonetheless, a limited flooding risk will
still be present.

&&

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

The long-term forecast remains on track, with a variable pattern
ahead. Another surface high pressure in the western Atlantic is
likely to migrate eastward and build over Central Atlantic,
promoting easterly trades through most of the period. The weather
conditions for early next week will most likely be seasonal, with
Precipitable Water (PWAT) values around 1.7 - 1.8 inches and 500 mb
temperatures between -7.5 and -8.0 Celsius. With increasing winds,
deep convection activity is expected to develop in the afternoon
mainly over portions of western Puerto Rico. Streamers created by
the local islands may also move into portions of eastern Puerto Rico
as well.

The deep upper-level trough northwest of the CWA is still expected
to approach the local area by Monday into Tuesday. Additionally, a
tropical wave located at approximately 32W is also anticipated to
approach the forecast area now on Monday evening into Tuesday. Based
on deterministic guidance from the GFS and ECMWF, the combination of
moisture associated to the tropical wave and the upper-level trough
will increase PWAT values to above climatological normal.
Additionally, colder 500 mb temperatures will enhance deep
convection activity. Hence, moderate to locally heavy rainfall
and thunderstorms mainly over the windward sections during the
night and early morning and into western portions of Puerto Rico
in the afternoon. The flooding potential will remain elevated for
the aforementioned areas.

Ensemble members agree that a less wet pattern for the second
part of the workweek is the most likely scenario due to the
approach of a Saharan Dust layer. From the latest guidance, the
highest concentrations should remain south of the region, but
uncertainty remains high. Under that scenario, deep convection
activity should remain limited with isolated thunderstorms in the
afternoon. However, the combination of daytime heating, local
effects, and available moisture may trigger showers in the early
morning over windward sections and western/northwestern Puerto
Rico in the afternoons.

By Thursday, decreasing winds from the southeast will pool warmer
and humid air into the local area. This is also reflected in the
925 mb temperatures, which will increase to above climatological
normal again. Hence, a limited risk of excessive heat is likely
and may affect most individuals sensitive to heat.

&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions will prevail across most terminals. Afternoon
SHRA/TSRA could cause mtn top obsc and brief MVFR/IFR at TJBQ
between 22/17-22Z. Calm to light and variable winds becoming more
easterly with sea breeze variations at 10-15 mph aft 22/14Z. Winds
become light and variable aft 22/22Z.

&&

.MARINE...

A building surface high pressure over the central Atlantic will
promote gentle to moderate easterly trades today, becoming moderate
to locally fresh by Friday. Isolated thunderstorms will continue to
develop across the regional waters, particularly across the northern
and western coastal waters of Puerto Rico each afternoon.

&&

.BEACH FORECAST...

The risk for rip currents will remain low today for all beaches
and coastal areas of the local islands. However, gradual increase
of winds will most likely promote a moderate risk of rip currents
by tomorrow Friday into the weekend. Beachgoers must exercise
caution.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
513 AM AST Fri May 23 2025

.KEY MESSAGES...

* Afternoon showers and thunderstorms are expected to develop each
afternoon across portions of central, western, and northern
Puerto Rico through early next week. Ponding of water in roads
and poor drainage areas and minor flooding are possible with
the strongest activity.

* Increasing winds will promote a moderate risk of rip currents in
St. Croix today, gradually spreading across Vieques, Culebra,
and northern and eastern beaches of Puerto Rico throughout the
weekend.

* An unstable and wetter weather pattern may return by the
beginning of the workweek, however, model guidance suggest an
area of suspended Saharan Dust approaching the Caribbean basin
that could limit shower and thunderstorm activity.

&&

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

Overnight satellite and radar observations indicated persistent
variable to mostly cloudy skies across the region. Scattered to
numerous showers and areas of persistent light rain were observed
over the local waters, with some moving across the U.S. Virgin
Islands, Vieques, Culebra, and eastern Puerto Rico. So far, the
highest rainfall totals, slightly over an inch, were estimated in
Humacao. Most of this rainfall occurred early in the night.
Overnight low temperatures ranged from the upper 60s in the higher
elevations to the mid to upper 70s across eastern and southern
Puerto Rico and the surrounding islands. Winds were generally light
and variable over Puerto Rico due to land breezes, while easterly
winds prevailed across the U.S. Virgin Islands. Expect similar
activity to continue for the rest of the morning hours. Winds were
generally light and variable over Puerto Rico due to land
breezes, while easterly winds prevailed across the U.S. Virgin
Islands. Wind gusts in the upper teens to lower 20s (mph) were
still reported at nearshore buoys, suggesting that higher gusts
may have reached coastal areas exposed to the wind.

The forecast remains on track, with a limited heat risk now expected
across urban and coastal areas of the islands through the short-term
period. This level of heat primarily affects individuals who are
extremely sensitive to high temperatures, particularly when outdoors
without effective cooling or adequate hydration. A slight adjustment
in the forecast includes a modest expansion of areas with higher
POPs for this afternoon, as the axis of the upper-level trough
continues to linger over the Leeward Islands. With the trough's
proximity still providing marginal instability aloft and sufficient
moisture, the probability of shower and thunderstorm activity has
increased.

Breezy conditions will persist through the weekend, as the pressure
gradient tightens across the northern Caribbean due to the
strengthening surface high over the central Atlantic. While faster
steering winds may somewhat limit rainfall accumulations this
afternoon, model soundings indicate unidirectional flow from the low
to mid-levels, which could still support training showers and
thunderstorms. This setup increases the potential for storms to
redevelop upstream and repeatedly impact the same areas.

As a result, under an east-southeast wind flow, expect shower and
thunderstorm development over the interior and northwestern portions
of Puerto Rico. Streamers downwind of the smaller islands, as well
as from El Yunque into the San Juan metro area, cannot be ruled out.
Overall, an elevated flooding threat is expected over western Puerto
Rico, with a more limited risk across the eastern third of the
island due to morning and afternoon shower activity. Southern Puerto
Rico is likely to experience minimal rainfall.

Similar weather conditions are expected through the weekend, with
slightly favorable dynamics aloft as the trough continues to shift
eastward. Shower and thunderstorm activity will follow the typical
diurnal pattern and will largely depend on moisture availability. On
Saturday, a limited flooding risk is expected across western Puerto
Rico during the afternoon, as moisture levels drop to below-normal
levels. By Sunday, moisture levels are expected to rebound,
resulting in a pattern similar to today, elevated flooding risk in
the west and a limited risk over eastern Puerto Rico due to
overnight and morning showers.


&&


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

A variable weather pattern is very likely for the next workweek.
A surface high pressure over the western Atlantic will build and
migrate eastward, promoting mostly southeasterly winds. The latest
model guidance highlights the approach of an upper- level trough
from the northeast of the local region that will bring instability
aloft. Additionally, the tropical wave located at 38W is likely
to approach the Caribbean but remain south of the forecast area by
Monday night. However, moisture associated with the tropical wave
will pool into the region, increasing low to mid-level moisture
content. Ensemble members keep agreeing, showing 40 - 50 % of
seeing near above- normal Precipitable Water values. In terms of
instability, lower 250 mb heights and colder 500 mb temperatures
(around -8.5 Celsius) should enhance deep convection.
Additionally, the Galvez- Davison Index (GDI) suggests the
potential of thunderstorm activity across the CWA during that
period. However, a factor that could limit deep convection
activity could be the Saharan Dust layer that is anticipated to
approach the Caribbean Basin now earlier than expected. But since
uncertainty remains high regarding the time of arrival and
considering local effects, the most likely scenario would be moderate
to locally strong showers and isolated thunderstorms moving over
the windward sections during Morning night, and early Tuesday,
while convection activity is likely to develop over interior and
western/northwestern Puerto Rico. Based on that, the flood threat
will remain elevated along the aforementioned areas.

From the latest discussion, the deterministic model guidance showed
GFS and ECMWF highlighting a less humid pattern for the second part
of the workweek. Ensemble members continue showing a decrease of
PWAT values to near below climatological normals by Wednesday due
to the Saharan Dust layer approaching the region earlier compared
to older solutions. Based on the latest guidance, the highest
concentrations should remain south of the CWA but most moderate
concentrations may be observed in the southern half of the
forecast area. This layer could inhibit the deep convection
activity during the afternoons, without triggering the upper-level
dynamics. However, as mentioned in the previous discussion,
available moisture below 850 mb levels, daytime heating, and local
effects would still enhance isolated showers and thunderstorms
mainly along interior and western/northwestern Puerto Rico.

Above-normal temperatures are still expected for the second part
of the workweek, being Thursday the warmest day. A limited risk
very likely along most urban and coastal areas of Puerto Rico and
the U.S. Virgin Islands, with an elevated threat along northern
and western portions of Puerto Rico.


&&


.AVIATION...

(06Z TAFs)

Afternoon SHRA/TSRA will generate MVFR to brief IFR conditions
across TJSJ/TJBQ between 23/16-22Z. VCSH possible across USVI
terminals throughout the period. Light and variable winds across PR
terminals and E winds at 5-10 knots across USVI terminals. Winds
will increase to 12-18 knots after 23/14Z, with sea breeze
variations and higher gusts, particularly near SHRA/TSRA.


&&


.MARINE...

A building surface high pressure over the central Atlantic will
promote moderate to locally fresh easterly winds for the next few
days. Isolated thunderstorms will continue to develop across the
regional waters, particularly across the western coastal waters of
Puerto Rico each afternoon. Hence, small craft should exercise
caution.


&&


.BEACH FORECAST...

For today, the risk of rip currents will remain low for the beaches
and coastal areas of Puerto Rico, St. Thomas and St. John, with
the exemption of St. Croix which is now under a moderate risk.
With winds increasing through the weekend, the moderate risk will
spread along northern and eastern beaches of Puerto Rico,
including Vieques and Culebra. Beachgoers must be aware of the
current conditions and exercise caution when visiting beaches
with possible life- threatening rip currents.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Sat May 24 2025

.KEY MESSAGES...

* There is a moderate risk of rip currents across the eastern and
northern beaches of the islands through early next week.

* Diurnally induced afternoon showers and isolated thunderstorms
are expected to develop mainly over western PR each afternoon.
Across the USVI and eastern PR, streamers are expected to
develop downwind of the islands and mountain areas.

* A moderate to strong Saharan Air Layer (SAL) with suspended
Saharan dust will move across the region on Monday and Tuesday.

* A weak tropical wave will enter the eastern Caribbean on Sunday,
increasing the chances of showers over the islands through
Monday.


&&

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

Mostly fair conditions prevailed in the night hours, with passing
showers moving occasionally over the local waters into eastern
portions of Puerto Rico and the U.S. Virgin Islands. Doppler radar
rainfall estimates did not surpass 0.10 inches. Minimum temperatures
remained in the upper 70s in the lower elevations, with some
stations reporting low 80s, while at higher elevations stations
indicated mid to upper 60s.

Current satellite-derived products show drier air mass filtering
into the region, along with showers embedded in the trades east
of the Leeward Islands. A broad surface high pressure
strengthening the Central Atlantic will continue promoting breezy
E-ESE winds for the next few days. A mid-to upper-level ridge
building northeast of the region will bring drier air into the
forecast area and enhance stability aloft. Ensemble members agree
that PWAT values are likely to decrease to below-normal values
(1.2 - 1.4 inches) today. However, passing showers should move
occasionally over windward sections during the morning. Although
faster winds should limit the deep convection activity, the
combination of local effects, seasonal 500 mb temperatures,
daytime heating, and the available moisture will increase the
potential of showers and isolated thunderstorms over western
Puerto Rico in the afternoon, with a limite risk of flooding. This
pattern should continue on Sunday, with a slight increase of PWAT
values that will elevate the flooding risk over the
aforementioned areas.

A dense layer of Saharan Dust located in the Central Atlantic is
expected to approach the Caribbean Basin by Monday, seeing moderate
concentrations in St. Croix before noon. Although this event could
limit deep convection activity, deterministic guidance from GFS and
ECMWF still highlight an increase of PWAT values over the local area
by Monday, meaning that isolated showers and thunderstorms may
develop in the afternoon over interior and western Puerto Rico.
Although the flooding risk will remain limited, rainfall
accumulations may promote ponding of water in roadways and poorly
drained areas. For the rest of the forecast area, expect hazy skies,
lower visibility, and deteriorate air quality, affecting people
sensitive to these particles.

Temperatures will be near above normal today, gradually decreasing
the next few days. Urban and coastal areas may expect maximum
temperatures in the upper 80s and low 90s, while higher elevations
should expect upper 70s to low 80s. Heat indexes will reach 100
Fahrenheit each day, nevertheless, the heat risk will remain
limited for most urban and coastal areas of Puerto Rico.

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

Hazy skies due to a lingering Saharan Air Layer with suspended
Saharan dust will continue on Tuesday. Although drier air aloft
will persist on Tuesday, sufficient low-level moisture content is
also expected, therefore, diurnally induced afternoon showers with
iso thunderstorms cannot be ruled over western PR. Then, through
at least Thursday, the area will remain under the influence of an
upper-level trough over Hispaniola and a weak mid-level ridge east
of the Leeward Islands. This will cause the 500 mb temperatures
to drop to around -8C and the precipitable content to remain near
1.75 inches, which is in the higher end of the 50th percentile for
this time of the year. Therefore, afternoon thunderstorms are
likely to develop over portions of the Cordillera and western PR.
These thunderstorms may cause strong gusty winds and locally heavy
rainfall that can lead to urban and small stream flooding. For
the end of the forecast cycle, the 500 mb temps are expected to
warm about 2 degrees, suggesting more stable conditions aloft.
However, at the lower levels, another tropical wave is forecast to
enter the eastern Caribbean and increase the precipitable water
content once again between 1.75 and 2.00 inches.


&&

.AVIATION...

(06z TAFs)

Mostly VFR conds for TAF sites. VCTS for TJBQ is likely due
SHRA/TSRA over western PR around 24/17z, which may bring brief MVFR
conds. E-ESE winds will increase to 15 -19 kt with higher gusts btw
26 - 28 kt after 25/14z, decreasing to 10 - 11 kt around 24/22z
24/23z.


&&

.MARINE...

A surface high pressure building over the North Atlantic Ocean will
promote moderate to locally fresh easterly winds through early next
week. A tropical wave will move mainly south of the region and across
the Caribbean Sea between Sunday and Monday. Isolated thunderstorms
are expected to develop across the western coastal waters of Puerto
Rico each afternoon.


&&

.BEACH FORECAST...

Increasing easterly winds and choppy wind-driven waves will
promote a moderate risk of rip currents through the weekend.
Therefore, life-threatening rip currents are possible across the
north and east facing beaches of the islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Sun May 25 2025

.KEY MESSAGES...

* There is a moderate risk of rip currents across the eastern and
northern beaches of the islands through midweek.

* Diurnally induced afternoon showers and isolated thunderstorms are
expected to develop mainly over western PR each afternoon.
Across the USVI and eastern PR, streamers are expected to develop
downwind of the islands and mountain areas.

* A moderate to strong Saharan Air Layer (SAL) with suspended
Saharan dust will move across the region on Monday and Tuesday.
Resulting in hazy skies, reduced visibilities and a
deterioration in air quality.


&&

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

Pockets of moisture moved frequently last night, mainly over the
local waters and windward sections of Puerto Rico and the U.S.
Virgin Islands, but Doppler Radar rainfall estimates remained low.
Winds slightly decreased during the night, however, gusty winds came
from time to time. Stations in Aibonito, Charlotte Amalie, and Lime
Tree Bay (St. Croix) reported wind gusts above 20 mph (26, 21, and
26 mph respectively). Stations across the CWA reported seasonal
minimum temperatures, as urban and coastal areas in the upper 70s
and low 80s. Interior portions of Puerto Rico remained in the 60s
with 62 Fahrenheit in Jayuya and 69 Fahrenheit in Villalba.

The short-term remains on track, with a variable weather pattern for
the beginning of this week. A surface high pressure building over
the Atlantic basin will promote an easterly wind flow for the rest
of the forecast period. Satellite-derived products show moisture
filtering into the region, bringing showers over the regional
waters, as mentioned in the previous discussion. Although the latest
global guidance suggests slightly below-normal values (1.4 - 1.5
inches), the combination of daytime heating and local effects will
increase the chance of afternoon convection. The 25/00z RAOB
reported 500 mb temperatures around -6 Celsius, slightly warmer
compared to the global model. However, it suggests that they
should cool enough by the afternoon, enhancing deep convection
activity. Therefore, moderate to locally heavy showers and
isolated thunderstorms are expected today mainly over western
Puerto Rico. Rainfall accumulations will likely increase the
potential of flooding, as the aforementioned areas have received
recent rainfall and soils remain saturated. Hence, expect ponding
of water in roadways and poorly drained areas, along isolated
urban and small streams flooding.

The Saharan Dust layer over the Central Atlantic is expected to
approach the local area on Monday, with moderate concentrations
reaching St. Croix during the morning. This type of event would
normally inhibit deeper convection activity, however, deterministic
guidance of the GFS and ECMWF still highlights an increase of PWAT
values on Monday afternoon into Tuesday due to the approach of an
upper-level trough and moisture associated with a tropical wave
located east of Barbados. Ensemble members agree that the most
likely scenario is to observe seasonal to near above climatological
normal mainly in the afternoons (1.6 - 1.8 inches). 500 mb
temperatures should remain seasonal on Monday but will get colder by
early Tuesday, increasing the potential of convective weather.
Additionally, the Galvez-Davison Index suggests this pattern for
Monday and Tuesday, with the potential of isolated thunderstorms
developing in western/northwestern Puerto Rico in the afternoon
alongside the San Juan streamer. Hence, the flood potential will
also remain limited to elevated but localized over these areas. For
the rest of the forecast area, expect moderate to locally high
concentrations that will bring hazy skies, lower visibility, and
deteriorate air quality, affecting people sensitive to these
particles.

With the Saharan Dust event coming in, temperatures should increase
to above normal. With the increase in moisture content, is very
likely to observe heat indexes above excessive heat criteria. Hence,
limited to elevated risk of heat is anticipated for most urban and
coastal areas of Puerto Rico and the U.S. Virgin Islands.


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

Hazy skies, caused by a lingering Saharan Air Layer with lesser
amounts of suspended Saharan dust than previous days, will continue
on Wednesday morning. Maximum temperatures are expected to range
from the upper 80s to low 90s across most coastal areas and urban
areas in the lower elevations of the islands for most of the period.
Breezy conditions are expected during the weekend under the
influence of a surface high pressure over the Central Atlantic and
the arrival of a tropical wave.

At least through Thursday, the area will remain under the influence
of an upper-level low over Hispaniola and a weak mid-level ridge
stretching from the Tropical Atlantic. In response, the 500 mb
temperatures are expected to drop to around -8°C and the
precipitable water content will fluctuate between 1.50 and 1.75
inches, which is about normal levels. Therefore, afternoon
thunderstorms will likely develop over the mountain ranges and
western Puerto Rico. These thunderstorms may produce strong winds
and locally heavy rainfall, which could lead to urban flooding and
small-stream flooding.

For the end of the week into the weekend, the ridge is expected to
build over the area, and the 500 MB temperatures are expected to
warm by about 2 degrees, indicating more stable conditions aloft.
However, another tropical wave is forecast to enter the eastern
Caribbean between Friday and Saturday, increasing the precipitable
water content to between 1.75 and 2.25 inches. This suggests a
wetter pattern over the islands, particularly on Saturday.


&&

.AVIATION...

(06Z TAFs)

Mainly VFR conds for all TAF sites. Moisture content will increase
today, bringing afternoon SHRA/TSRA over western PR and possible
VCTS for JBQ around 25/18z, which may slightly reduce CIG/VIS. VCSH
should move over IST and ISX after 25/23z. Breezy conds will
continue today, with E winds btw 15 - 20 kt and gusts up to 30 kt
after 25/13z, slowing down btw 7 - 11 kt after 25/23z.


&&

.MARINE...

A surface high pressure building over the Atlantic Basin will
promote moderate to locally fresh easterly winds through next week.
A tropical wave will move mainly south of the region and across the
Caribbean Sea from late today through Monday. Isolated thunderstorms
are expected to develop across the western coastal waters of Puerto
Rico each afternoon. Hazy skies and reduced visibilities are
expected on Monday and Tuesday due to Saharan dust.


&&

.BEACH FORECAST...

Increasing winds will result in beaches reaching a moderate risk of
rip currents, mainly for the eastern and northern half of Puerto
Rico, Vieques, Culebra, and for all of the Virgin Islands. Life-
threatening rip currents could occur in these places.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
527 AM AST Mon May 26 2025

.KEY MESSAGES...

* A moderate to high Saharan Air Layer (SAL) event is expected
from today through early Wednesday, resulting in hazy skies,
reduced visibilities and deteriorated air quality across the
region.

* A surge of moisture associated with a tropical wave moving south
of the region, will promote the entrance of fast-moving showers
throughout the day.

* Breezy conditions will result in a moderate risk of rip currents
along the northern, eastern and southeastern beaches of Puerto
Rico, Vieques, Culebra, and St. Croix. Beachgoers, please take
caution while vising the local beaches this week.


&&

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

A tropical wave moving south of the region will continue to increase
moisture content from the surface to around 700 MB today. At the
same time a strong Saharan Air Layer will continue to filter over
the eastern Caribbean, bringing drier air aloft and gradually
increasing Saharan dust particles over the islands. An upper-level
low is expected to develop over Hispaniola by early Tuesday morning
and linger just west of the region through the short-term period.
This will cause the 500 MB temperatures to drop to near -8C and
promote somewhat unstable conditions over the area. Therefore,
expect a mixture of hazy skies with increasing cloudiness today as
showers continue to develop across the Caribbean waters and over the
islands under the influence of tropical wave and the diurnal cycle
of afternoon convection over the mountain areas of Puerto Rico.

Hazy skies due to moderate to high concentrations of Saharan dust
will persist through Tuesday, with lesser concentrations lingering
on Wednesday. A drier air mass is expected to move over the area
from the east between Tuesday and Wednesday, and the precipitable
water content is forecast to drop from over 2 inches today to near
1.50 inches by Wednesday morning. Having said that, the proximity of
the upper-level low and the colder 500 MB temperatures in
combination with the available low-level moisture content, daytime
heating, the sea breeze convergence, and other local effects will
induce the development of afternoon showers and isolated
thunderstorms each afternoon over western Puerto Rico. Additional
showers from streamers developing downwind of the U.S. Virgin Islands
and eastern PR are also expected to develop around noon each day.

Warmer than normal temperatures are expected on Tuesday and
Wednesday, with max temps ranging from the upper 80s to low 90s
along the lower elevations and urban areas of the islands. However,
heat indices today could increase btw 102F-108F before the onset of
afternoon showers.

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

A building surface high pressure strengthening over the central
Atlantic will maintain east to southeast winds throughout the
forecast period. By Friday, a tropical wave is expected to move over
the northeastern Caribbean, increasing moisture across the region
with precipitable water values (PWAT) around 2.0 inches. In
response, temperatures in the 500 mb are expected to decrease to -
8°C, increasing the potential to observe thunderstorm activity
across portions of central and northwestern Puerto Rico. However,
after the wave passage conditions will become more stable aloft as
a mid-to-upper level ridge begins to build over the area from
Saturday onward.

The latest precipitable water (PWAT) guidance suggest normal
climatological values during the weekend of 1.5 to 1.8 inches.
Despite the drier conditions and stability aloft, showers are
anticipated to develop across portions of western Puerto Rico due
to daytime heating, sea breeze convergence and orographic
effects.

Low concentrations of suspended Saharan Dust particles will continue
to reach the local islands over the weekend, promoting hazy skies
through at least early next week. The 925 mb temperatures will
remain at normal to above normal climatological values during the
weekend, particularly over the northern, western and southern
coastal areas of Puerto Rico. Highs will remain in the range from
the upper 80s to low 90s across the coastal and urban areas, and in
the upper 70s to low 80s in the higher mountains. Heat indices will
reach the 100°F each day, particularly on Friday and Saturday.

&&

.AVIATION...

Mainly VFR conds expected. However, a tropical wave moving across
the Caribbean Sea will increase SHRA/TSRA over the local area today.
This may lead to brief MVFR conds, particularly at TJSJ/TJBQ fm
26/16z-22z. HZ and reduced VSBY due to Saharan dust will prevail
through at least late Tuesday. E to ESE winds btw 14-18 kt with
stronger gusts and sea breeze variations expected aft 26/14z.

&&

.MARINE...

A surface high pressure building over the Atlantic Basin will
promote moderate to locally fresh easterly winds through this week.
A tropical wave will move south of the region and across the
Caribbean Sea today. Isolated thunderstorms are expected to develop
across the western coastal waters of Puerto Rico each afternoon. Hazy
skies and reduced visibilities are expected through mid-week as
Saharan dust moves over the region.

&&

.BEACH FORECAST...

Breezy conditions will continue to promote a moderate risk of rip
currents along the northern, eastern and southeastern beaches of
Puerto Rico, Culebra, Vieques and St. Croix through this week.
Although the risk for rip currents is low elsewhere, life-
threatening rip currents often occur in the vicinity of groins,
jetties, reefs, and piers.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
436 AM AST Tue May 27 2025

.KEY MESSAGES...

* A moderate to high Saharan Air Layer (SAL) event will continue
to affect the northeastern Caribbean through early Wednesday,
resulting in hazy skies, reduced visibilities and deteriorated
air quality across the region.

* Showers and isolated thunderstorms are expected to develop
mainly over central and western Puerto Rico each afternoon
while streamers are expected to develop downwind of the islands
and mountain areas.

* Another dense plume with higher concentrations of Saharan dust
will return early next week. Please take the necessary
precautions, particularly for adverse conditions for
immunocompromised, vulnerable and sensitive groups.

&&

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

Light showers were noted across the northern coastal and eastern
sections of Puerto Rico, as well as across the U.S. Virgin Islands
throughout the early morning hours. The Doppler radar estimated
under a tenth of an inch of rain with this activity. Isolated
thunderstorms and heavier showers were noted over the northwestern
coastal and offshore Atlantic waters of PR. Minimum temperatures
were from the mid-60s across the higher elevations of PR to the mid-
70s and low-80s across the lower elevations of PR and the USVI. The
wind was from the east at less than 10 mph with lighter land breeze
variations.

Moderate to high concentrations of Saharan dust will continue today
over the eastern Caribbean. This will continue to cause hazy skies
across all the islands and local waters. An upper-level low is
expected to develop over Hispaniola today and linger just west of
the region through the rest of the short-term period. This will
promote marginal unstable conditions aloft as the area remains under
the right quadrant of the low, increasing upper-level divergence and
promoting colder 500 MB temperatures of around -7.5C. Therefore,
diurnally induced afternoon showers with isolated thunderstorms are
expected to develop mainly over western PR, and downwind from the
USVI and the eastern interior of PR. In general, moderate to locally
fresh trade winds are expected throughout the day, with a slight ENE
component by this afternoon. Therefore, afternoon showers will focus
over west/southwestern PR, and limit somewhat the potential for
higher than normal heat indices along coastal and urban areas.
Regardless, max temps are still forecast to range from the mid-to
upper-80s across the eastern and northern portions of the islands,
to the upper-80s and low-90s across the southwest to western areas.

For Wednesday and Thursday, a drier air mass is expected to move
over the area from the east and the precipitable water (PWAT)
content is forecast to drop from around 1.80 inches today to near
1.40 inches by Thursday afternoon. This is expected to promote fair
weather conditions overall across the islands. However, shallow
pockets of moisture embedded in the trade winds will cause some
fluctuations in the PWAT at times, particularly during the night,
when mostly passing showers are expected across the USVI and eastern
sections of PR. Also, locally induced afternoon showers with brief
thunderstorms are still expected to develop each day over western
PR.

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

A tropical wave will move south of the region from Friday into
Saturday, increasing moisture across the region. The bulk of the
moisture will remain south of the area on Friday with limited
impacts over the area. However, as the wave moves toward the
Dominican Republic, some moisture associated with the wave will
reach portions of the Mona Passage and western Puerto Rico.
Therefore, showers and isolated thunderstorms cannot be ruled out
over this region, particularly on Friday afternoon into the evening.
A second tropical wave is expected to move fast south of the area on
Saturday night into early Sunday with very limited impacts over the
region. The latest precipitable water content (PWAT) guidance
suggest seasonal climatological values during the weekend period
(1.6 to 1.8 inches).

As the weekend progresses a mid-to-upper level ridge will build over
the northeastern Caribbean promoting stability aloft and drier
conditions. With the 500 mb temperatures expected to warm up to near
above normal values of -6°C and -7°C through early next week. At the
surface, a strong high pressure in the central Atlantic will promote
southeasterly winds and the entrance of a drier air mass on Sunday,
that is expected to last through mid-week. A dense plume of Saharan
Air Layer will reach the islands by early next week, with moderate
to high concentrations of dust particles. Therefore, expect hazy
skies, reduced visibilities and and poor air quality next week. Warm
to hot temperatures are expected too, with temperatures in the 925
mb at above normal climatological values during the weekend into
next week, particularly over the northern, western and southern
coastal areas of Puerto Rico. Highs will remain in the range from
the upper 80s to low 90s across the coastal and urban areas, and in
the upper 70s to low 80s in the higher mountains.

&&

.AVIATION...

Mainly VFR conds expected across all terminals during the next 24
hours. However, locally induced SHRA/TSRA expected to develop over
western PR btw 27/16z-22z. This should cause mostly VCTS at TJBQ.
Elsewhere, VCSH expected. HZ due to Saharan dust will continue today
with periods of reduced VSBY at times. East winds will increase btw
12-16 kt with stronger gusts and sea breeze variations aft 27/14z.

&&

.MARINE...

A surface high pressure building over the Atlantic Basin will promote
moderate to locally fresh easterly winds this week. Isolated
thunderstorms are expected to develop across the western coastal
waters of Puerto Rico each afternoon and evening. Hazy skies and
reduced visibilities are expected through mid-week as Saharan dust
moves over the region.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents for the northern and eastern
beaches of Puerto Rico, and St. Croix. Although the risk for rip
currents is low elsewhere, life-threatening rip currents often
occur in the vicinity of groins, jetties, reefs, and piers. A
low risk of rip currents will return tomorrow for all islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Wed May 28 2025

.KEY MESSAGES...

* Hazy conditions will gradually diminish today as the higher
concentrations of Saharan Dust continues to move away from the
region.

* Showers and isolated thunderstorms are expected each afternoon
across central and western Puerto Rico, mainly due to diurnal
heating, orographic effects and sea breeze convergence.

* A dense plume of Saharan Dust will return by early Sunday. High
concetrations of dust will persist across the area through next
week. Please take the necessary precautions, particularly for
adverse conditions for immunocompromised, vulnerable and
sensitive groups.

&&

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

Quick passing showers left between a tenth to a quarter of an inch
of rain over portions of northeastern Puerto Rico during the early
morning hours. Less activity was observed across the U.S. Virgin
Islands. Minimum temperatures were from the low to mid-60s across
the higher elevations of PR to the mid-70s and low-80s across the
lower elevations and across the USVI. The wind was from the east to
northeast around 10 mph with gusts up to 20 mph.

The islands will remain between an upper-level low to the west and a
building ridge from the east through at least Thursday. By Friday,
the low is expected to open into a trough and move eastward into the
Atlantic waters. The 500 MB temperatures are forecast to range from
around -7C today to -9C by Friday afternoon. Although this will
increase instability over the area, the overall precipitable water
content is forecast to remain at normal to below normal levels (1.40-
1.60 inches) throughout the short-term period, as plenty of drier
air between the 700-500MB layer filters from the east under the
building ridge. Having said that, the latest IR satellite imagery
indicated plenty of shallow low-level cloudiness across the Tropical
Atlantic, and an active tropical wave far south near 50W. Therefore,
an overall fair weather pattern is anticipated across the islands,
with the exception of brief passing showers moving at times across
the USVI and eastern PR, leaving minor rainfall accumulations.
Across western PR, the combination of the limited available moisture
with daytime heating, the sea breeze convergence and orographic
effects will cause showers to develop each afternoon, with a chance
of thunderstorms due to the proximity of the upper-level low.

The hazy conditions will gradually diminish today as the higher
concentrations of Saharan dust are now mainly west and south of the
region. Daytime highs will range from the mid-80s to low-90s across
the lower elevations of PR, and in the upper-80s across the USVI.
However, under east to northeast winds the heat indices are expected
to remain below heat advisory criteria through at least Thursday. On
Friday, winds will turn more east to southeast, resulting in warmer
temperatures and increasing the heat threat across portions of the
lower-elevations of the islands.

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

Hazy and dry conditions are expected for the forecast period as a
dense plume of Saharan Air Layer (SAL) moves across the northeastern
Caribbean. The latest model guidance indicates aerosol optical
thickness values of 0.4 and 0.5 starting on Saturday night over the
U.S. Virgin Islands, then moving over Puerto Rico by early Sunday.
This event will promote, once again, hazy skies, reduced
visibilities and deteriorated air quality. Due to the amplitude of
the SAL, hazy conditions are expected to persist through at least
the end of the workweek. Residents and visitors are urged to take
the necessary health precautions during this period.

At the surface a strong high pressure over the central Atlantic will
continue to promote moderate to locally breezy southeasterly
winds for most of the period, and shifting from the east by mid-
week. A mid-to-upper level ridge will build across the region,
promoting stability aloft and inhibiting deep convection across
the area. Therefore, very limited showers and few isolated
thunderstorms are expected over the interior and northwestern
Puerto Rico. The latest precipitable water content (PWAT) has
values between 1.35 to 1.50 inches, with the drier days being from
Tuesday onward. Under the aforementioned pattern, warm to hot
temperatures will return with temperatures in the 925 mb at above
normal climatological values, particularly over the northern,
western and southern coastal areas of Puerto Rico and St. Croix.
Highs will remain in the range from the upper 80s to low 90s
across the coastal and urban areas, and from the upper 70s to mid
80s in the higher elevations.

&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
through the forecast period. However, between 28/16z-21z, locally
induced SHRA/TSRA over the interior and western PR should cause
mostly VCTS at TJPS/TJBQ. Elsewhere, VCSH expected, particularly aft
28/22z. HZ due to Saharan dust will continue today but VSBY will
remain P6SM. E to ENE winds will increase btw 12-16 kt with stronger
gusts and sea breeze variations aft 28/14z.

&&

.MARINE...

A surface high pressure building over the Atlantic Basin will promote
moderate easterly winds today and are expected to strengthen by the
end of the workweek into the weekend. Isolated thunderstorms are
expected to affect the western coastal waters of Puerto Rico and the
Mona Passage each afternoon and evening, where small craft should
exercise caution. Hazy skies and reduced visibilities are expected
through mid-week as Saharan dust moves over the region.

&&

.BEACH FORECAST...

There is a moderate risk of rip current for Saint Croix. The rip
current risk will remain low for the rest of the coastal areas of
Puerto Rico and the northern U.S. Virgin Islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
358 AM AST Thu May 29 2025

.KEY MESSAGES...

* Today, mainly fair weather conditions are expected across
Puerto Rico and the U.S. Virgin Islands with the presence of a
mid- level ridge in our region.

* Showers and isolated thunderstorms are expected each afternoon
across central and western Puerto Rico, mainly due to diurnal
heating, orographic effects and sea breeze convergence.

* A dense layer of Saharan Dust is expected to gradually spread
across the area starting Saturday evening. Please take the
necessary precautions, particularly for adverse conditions for
immunocompromised, and sensitive groups.

&&

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

Satellite imagery indicated a persistent mid- to high-level cloud
layer associated with a trough to the west. Later in the evening and
continuing overnight, radar detected scattered showers, primarily
over windward areas and coastal areas, moving in from the local
waters. After some clearing, increased showers were carried by
breezy east to east-northeast winds ranging from 10 to 15 mph, with
occasional stronger gusts. Rainfall amounts overnight were generally
light. Minimum temperatures remained mild, mainly in the mid-to-
upper 70s. However, some coastal areas stayed in the lower 80s,
while slightly cooler temperatures were observed inland across the
mountain valleys.

Mostly stable conditions will prevail through Friday, influenced by
a mid-level ridge that maintains a trade wind cap and drier air
aloft, limiting widespread shower development. However, an upper-
level trough lingering over the northeastern Caribbean will
contribute marginal instability, supporting isolated thunderstorms
during the afternoon hours, driven by diurnal heating and sea-breeze
convergence. Overnight and early morning periods will continue to
feature brief trade wind showers, mainly over windward and elevated
terrain. Breezy east-to-east-southeast winds will persist,
potentially causing hazardous marine conditions and increased wind
exposure along the coast and local islands. These winds will also
promote a gradual warming trend, bringing limited to elevated heat
risks to urban and coastal areas.

Conditions will gradually shift late Friday into Saturday as the mid-
level ridge weakens, a trough sets up favorably aloft, and an
approaching tropical wave, along with an easterly wind disturbance,
enhances moisture across the region. This transition will push
precipitable water values to above-normal levels, which, combined
with cooler-than-normal temperatures at the 500 mbar level, will
foster more favorable conditions for shower and thunderstorm
development, as supported by the Galvez-Davidson Index.

However, a dense layer of Saharan dust is expected to gradually
spread across the area starting Saturday evening. Despite the
presence of drier air associated with the dust, cooler mid-level
temperatures and lingering instability will continue to support
isolated thunderstorm development. While the dust may reduce
rainfall efficiency and degrade air quality, it could also
contribute to warmer surface temperatures. This added heating may
further enhance atmospheric instability, potentially leading to more
frequent lightning activity within developing storms. Localized
heavy rainfall could result in minor flooding, especially in flood-
prone or poorly drained areas where downpours persist.

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

A dense plume of Saharan Air Layer (SAL) is expected to affect the
northeastern Caribbean through mid-week. The latest model guidance
continues to suggest high dust concentrations with aerosol optical
thickness of 0.4 and 0.5. As a result, hazy skies, deteriorated air
quality and reduced visibilities are anticipated throughout the
week. Residents and visitors are urged to take the necessary
health precautions during this period.

A strong surface high pressure over the central Atlantic will
promote southeasterly winds through Tuesday. Then, winds are
expected to become from the east as the surface high migrates over
the northeastern Atlantic. The forecast have been consistent with
the arrival of a drier airmass into the region by Sunday onward.
In addition, a mid- level ridge will build over the central
Atlantic and near our region, promoting stable conditions aloft
and fair weather with limited showers over the islands. Under the
aforementioned pattern, the temperatures at the 925 mb will
increase to above-normal climatological values by early next week.
Expect temperatures to rise into the upper 80s and low 90s across
the coastal areas, with heat indices reaching values over 105°F.
Residents and visitors are encouraged to continue monitoring the
weather conditions as the weekend progresses.


&&

.AVIATION...
(06Z TAFs)

There is a chance for VCSH across all USVI terminals and
TJSJ through most of the period. Afternoon SHRA/TSRA may develop,
particularly affecting TJSJ and TJBQ between 29/17-22Z, with brief
periods of MVFR conditions possible. Winds will be from the east to
northeast at 8–10 knots, increasing to 15–20 knots with higher gusts
and sea breeze influences after 29/13Z. Winds are expected to
diminish after 29/22Z. Gusty conditions may also occur in and around
any strong TSRA.

&&

.MARINE...

A surface high pressure building over the Atlantic Basin will promote
moderate to locally fresh easterly winds over the next few days.
Small craft should exercise caution across most offshore waters and
local Caribbean passages. Isolated thunderstorms are expected to
affect the western coastal waters of Puerto Rico and the Mona Passage
each afternoon and evening. Low concentrations of Saharan Dust will
remain over the region the rest of the week, then hazy skies and
reduced visibilities are expected during the weekend and early next
week as another dense plume of Saharan dust moves toward the area.

&&

.BEACH FORECAST...

There is a moderate risk of rip current for the northwestern and
north-central beaches of Puerto Rico, Culebra and Saint Croix.
The rip current risk will remain low for the rest of the coastal
areas of Puerto Rico and the northern U.S. Virgin Islands. Please
keep in mind that life-threatening rip currents often
occur in the vicinity of groins, jetties, reefs, and piers.

&&

[TomballEd]

The next wave of SAL coming off Africa (it shows up in visible imagery) is a big one. After affecting the Caribbean it will affect the US Gulf of Mexico coast late next week.

https://www.tropicaltidbits.com/sat/satlooper.php?region=eatl&product=truecolor

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Sat May 31 2025

.KEY MESSAGES...

* An extensive and dense plume of Saharan Air Layer (SAL) will
affect the local islands from today into the middle of the
upcoming workweek. This will result in hazy skies, limited
coverage in shower activity, and warmer conditions.

* An increase in surface winds will induce some moderate to
locally fresh winds, resulting in wind-driven seas. Therefore,
small craft operators should exercise caution.

&&

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

A cloud deck present in the mid-to-upper levels of the atmosphere
contributed to variably cloudy skies overnight across the region.
Additionally, the arrival of a Saharan Air Layer (SAL) resulted in
somewhat hazy conditions. Overnight low temperatures ranged from the
mid-60s in the mountain regions to the mid-70s along the coastal
areas. Doppler radar detected a few isolated showers developing
along the windward sections of the islands, advected by an east-
southeast wind flow, but localized land breeze effects were also
noted.

A mid-level ridge nearly stationary over the region will continue to
support a trade wind inversion, effectively suppressing deep
convective development across Puerto Rico and the U.S. Virgin
Islands. This synoptic pattern, combined with the arrival of a
Saharan Air Layer (SAL), will further dry out the atmosphere above
850 MB, limiting vertical moisture availability over the northeast
Caribbean. Despite this drying trend, pockets of moisture embedded
within the prevailing winds, associated with a wind surge, will
bring occasional showers across portions of the islands, especially
in the windward locations. As the wind surge progresses, residents
can expect a noticeable increase in local winds throughout the
weekend, especially during the late morning and afternoon hours.

Afternoon convection will remain confined to the northwest quadrant
of Puerto Rico, driven by local sea breeze convergence and diurnal
heating, but widespread thunderstorm activity is not anticipated due
to the prevailing dry air and stable conditions. The SAL, expected
to arrive later today and persist into early next week, with a peak
around Monday, is likely to result in hazy skies, reduced
visibility, and minimal rainfall. As SAL concentrations increase,
nighttime radiational cooling will be limited, leading to warmer-
than-average minimum temperatures each night and early morning hours
across the islands. Therefore, we expect a warm to hot period in the
coming days, with elevated heat indices and above-normal
temperatures.

The presence of Saharan dust will lead to hazy skies and reduced air
quality across the region. Individuals with respiratory conditions,
such as asthma or allergies, should limit outdoor activities and use
protective measures as needed. Staying hydrated and avoiding
strenuous outdoor exercise during peak heat hours is also
recommended.


.LONG TERM...Tuesday trough Saturday...

The long-term forecast remains on track. According to the NASA
Goddard Earth Observing System Model V5, a dense plume of Saharan
Air Layer (SAL) will continue to affect the northeastern Caribbean
through midweek. The model indicates that the highest
concentrations are expected early in the period, with aerosol
optical thickness values nearing 0.5. This pattern will result in
hazy skies, reduced visibilities, and deteriorated air quality
through at least Wednesday. Although the most intense dust
presence is forecast for the first part of the week, low to
moderate concentrations are expected to linger into the upcoming
weekend. Residents and visitors, particularly those with
respiratory conditions, are advised to take appropriate health
precautions during this period. At the surface, a high-pressure
system will promote southeasterly winds through Tuesday, gradually
shifting from the east as the high moves into the central
Atlantic.

A mid- to upper-level ridge is forecast to strengthen over the
region during the early part of the week, favoring a drier and
more stable environment aloft. Precipitable water values will
remain below climatological normals, near or below 1.5 inches,
limiting overall shower activity across the area. However, locally
induced showers and isolated thunderstorms remain possible each
afternoon across western Puerto Rico, due to diurnal heating and
local effects. Temperatures will remain above normal, with highs
ranging from the upper 80s to low 90s Fahrenheit in coastal and
urban areas, and in the low 80s across higher elevations. Heat
indices may exceed 108°F during the peak of the event,
particularly across north-central Puerto Rico. These hot and dry
conditions, combined with poor air quality, could pose additional
health risks, especially for the more vulnerable populations.

&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions across the terminals. Any SHRA will be
briefed, with minimal impact on operations for most terminals.
Expect winds from the ESE to range at 15-20 kts after 31/13z, with
higher gusts around 25 kt or more. However, they are expected to
return to 10 kt or less overnight (after 31/22z). VCSH will develop
near TJBQ during the afternoon hours, but we are not anticipating
widespread activity. A SAL will bring hazy skies, but visibility
will range around 6SM, especially from this afternoon onward.

&&

.MARINE...

A surface high-pressure system strengthening over the Atlantic
Basin will continue to support moderate to locally fresh easterly
trade winds during the next few days. Mariners should remain
cautious, particularly across offshore Atlantic waters and the
Caribbean passages, where choppy seas are expected. Each afternoon
and evening, isolated thunderstorms may develop and impact the
Mona Passage and western coastal waters of Puerto Rico due to
localized convergence. By late today into the middle of next
week, another significant surge of Saharan dust is forecast to
reach the region, leading to hazy skies and reduced visibility.

&&

.BEACH FORECAST...

A moderate risk of rip currents is in effect for north-facing
beaches of Puerto Rico and the island of Saint Croix. Elsewhere,
the risk remains low. Nonetheless, swimmers are urged to use
caution, especially near piers, reefs, and other structures where
dangerous rip currents are more likely to form unexpectedly.

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
425 AM AST Sun Jun 1 2025

.UPDATE...

* Hazy skies and limited shower activity will persist today due to
the presence of Saharan dust particles over the islands.

* Warmer conditions will remain in place due to a southeasterly
wind flow across the islands. Therefore, a Heat Advisory is in
effect for most coastal areas of Puerto Rico from 10 AM to 4 PM.

* Improving weather conditions are forecast from Tuesday onward.

&&

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

Hazy skies limited nighttime cooling, resulting in warmer-than-
normal minimum temperatures across Puerto Rico and the US Virgin
Islands. Overnight low temperatures ranged from the mid-to-upper 60s
in the mountain regions to the upper 70s or even the low 80s along
the lower elevations. The Doppler Radar detected a few isolated
showers brought by the east-southeasterly wind, moving inland across
windward sections of the islands.

A relatively stable weather pattern is forecast for Puerto Rico and
the US Virgin Islands through Tuesday, as indicated by model
guidance. This pattern will be characterized by near-to-below-normal
moisture content, a dense Saharan Air Layer (SAL), and the influence
of a mid-level high pressure. The high pressure will promote a trade
wind inversion, capping convection and limiting significant vertical
development of clouds. In addition, a dense concentration of
suspended dust particles will persist over the region. The SAL will
result in degraded air quality and hazy skies across the islands.
The SAL will also contribute to warmer-than-normal temperatures,
especially during nighttime hours, reducing radiational cooling and
contributing to hotter minimum temperatures each morning.

With a suppressed convective environment and limited instability, we
anticipate brief and fast-moving showers, primarily across the
windward areas of PR and the USVI, driven by a breezy east-southeast
wind flow. These showers may occasionally move inland due to a low-
level wind surge that enhances moisture advection. During the
afternoons, limited convective development is expected along western
PR and downwind from the USVI, although widespread rainfall is not
anticipated. Model guidance supports this outlook, showing relative
stability in the mid-levels, with 500 MB temperatures near normal
and a pronounced lapse rate inversion limiting vertical mixing and
thunderstorm development.

Heat-related impacts, however, are of increasing concern. The
combination of persistent SAL, reduced overnight cooling, and rising
daytime temperatures will elevate the heat index values each
afternoon. The 925 MB temperature model guidance confirms hotter-
than-average temperatures at low levels, suggesting that heat
advisories or even excessive heat warnings may be required each day
between 10 AM and 4 PM, at least starting today, Sunday. While we
expect a gradual decrease in dust concentration by Tuesday
afternoon, hazy skies will likely linger until a cleaner air mass
replaces the SAL. Residents should remain alert for updates on heat-
related advisories and take precautions to mitigate heat stress,
especially in urban and poorly ventilated areas. Individuals with
respiratory conditions, such as asthma or allergies, should follow
their medical recommendations and use protective measures as needed.

.LONG TERM...Wednesday trough Sunday...

A broad surface high over the central Atlantic and an induced
trough north of the western Atlantic will maintain an easterly
wind flow across the local islands on Wednesday. This pattern will
support the advection of shallow patches of moisture, with
precipitable water values ranging from 1.2 to 1.7 inches. Global
model guidance suggests limited to no lingering Saharan Air Layer
(SAL) presence, resulting in improved visibility and reduced haze.
Subsidence aloft associated with a strengthening mid- to upper-
level ridge will promote a stable atmosphere, suppressing deep
convection across much of the region. However, locally induced
showers and isolated thunderstorms remain possible across western
Puerto Rico during the afternoon due to diurnal heating and local
convergence. From Friday through Sunday, a gradual shift in the
low-level wind flow toward a more southerly component is expected,
favoring weak warm air advection. This will likely result in
elevated temperatures across the northern coastal and interior
sections of Puerto Rico, with warmer conditions extending into the
U.S. Virgin Islands. Under mostly sunny skies and continued mid-
level subsidence, heat indices could reach or exceed advisory
thresholds. Residents are encouraged to stay hydrated and follow
official heat safety recommendations during this period.

&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions across the terminals. A dense Saharan Air
Layer will limit visibilities between 5 and 9 SM. Any SHRA will be
briefed, with minimal impact on operations for most terminals.
Expect winds from the ESE to range at 15-20 kts after 01/13z, with
higher gusts around 25 kt or more. Once again we expect winds to
range at 10 kt or less overnight (after 01/23z). VCSH will develop
near TJBQ during the afternoon hours, but we are not anticipating
widespread activity.

&&

.MARINE...

A broad surface high pressure extending across the Atlantic basin
will maintain a moderate to locally fresh east-southeasterly wind
flow across the local waters. As a result, seas will remain up to
5 feet, with locally higher seas of up to 6 feet due to wind-
driven waves. Small craft operators should exercise caution across
the exposed local waters today and through the upcoming workweek.
Increasing in surface wind is forecast again by late Tuesday into
Wednesday, resulting in wind driven seas again.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents along the southern
coastal areas, particularly in the southwestern region, St. Croix,
Culebra, and Vieques. The risk will increase for the remaining
southern coastal areas tonight. On Wednesday, the moderate risk of
rip currents will extend across the northern coast of Puerto Rico
and the rest of the islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
415 AM AST Mon Jun 2 2025

.KEY MESSAGES...

* A dense Saharan Air Layer will continue to cause hazy skies.
Dry and stable conditions will persist early in the week.

* Hot temperatures are anticipated once again today. This level of
heat affects most individuals sensitive to heat, especially
those without effective cooling or adequate hydration.


&&

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

During the overnight hours, a very stable weather pattern prevailed
across the region, with mostly clear and hazy skies due to the
ongoing presence of Saharan dust. Minimal cloud development was
observed, and no significant shower activity occurred. Temperatures
remained slightly above climatological normals, with coastal areas
generally in the low 80s, while conditions were noticeably cooler in
the higher elevations of the interior mountains.

A stable and dry weather pattern will continue through Tuesday,
supported by a mid-level ridge and the presence of Saharan dust over
the region. A broad surface high over the central Atlantic will
promote southeasterly winds, resulting in hazy skies, above-normal
temperatures, and limited rainfall. For today, a Heat Advisory
remains in effect from 10 AM through the afternoon at 4 PM AST for
northern, western, and southern coastal areas of Puerto Rico due to
warm low-level temperatures and persistent southeasterly winds.
Atmospheric moisture is running below normal, and mid-level humidity
is limited, which will inhibit vertical cloud development. While
overall chances for rainfall remain low, brief afternoon showers
driven by local effects may still occur across northwestern
sections. On Tuesday, the heat will be slightly less intense as
winds shift more from the east and an even drier air mass moves in,
with moisture levels falling well below normal. This will reinforce
stable conditions, resulting in minimal shower activity.

By early Wednesday, patches of fragmented moisture are forecast to
move into the region, bringing a slight increase in quick-moving,
light to moderate showers during the morning hours. With Saharan
dust concentrations decreasing and moisture values trending back
toward seasonal levels, instability is expected to improve slightly.
This may allow for more widespread and stronger afternoon convection
on Wednesday, particularly across interior and western Puerto Rico,
under more favorable thermodynamic conditions compared to earlier in
the week.

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

A mid to upper level high will maintain stable conditions aloft
through the end of the week. At the surface, high pressure
centered over the eastern Atlantic will keep the trade wind
strong, around 15 to 20 knots, out of the east or southeast.
On Thursday, a weak trough will sneak in, though, mostly working
to enhance the shower activity in the afternoon across western
Puerto Rico. Later on Friday and the weekend, the trade wind cap
inversion develops again, trapping all the moisture to the lowest
levels of the atmosphere. Chances of showers will be limited to
afternoon convection across the west, and a few showers streaming
into the Virgin Islands or eastern Puerto Rico. Some Saharan dust
will filter in too, especially by the end of the week.
Concentrations are not expected to be high, however. Then, on
Monday, there is going to be an increase in moisture as a tropical
wave approaches. Through the forecast period, temperatures will be
seasonably warm, with highs in the upper 80s and low 90s, and heat
indices just above 100 degrees for most of the coastal and urban
areas of the local islands.

&&

.AVIATION...
(06Z)
VFR conditions will persist across all TAF sites
during the period. Saharan dust particles will induce a reduction in
VIS and lower flight-level ceilings in some areas. In general, winds
will remain VRB, increasing by 02/15Z, becoming from the E-SE at 15
knots with gusty winds. Showers are not forecast across or near TAF
sites.

&&

.MARINE...
A surface high pressure over the Atlantic Basin will continue to
promote moderate to locally fresh trade winds over the next few days.
Southeast winds will prevail through Monday, becoming more easterly
through the rest of the week. Small craft should exercise caution
across portions of the offshore waters and local Caribbean passages.
Hazy skies and reduced visibilities are expected to continue through
at least Tuesday due to high concentrations of Saharan dust over the
region.

&&

.BEACH FORECAST...
Breezy winds from the southeast will maintain a moderate rip
current risk for the southern beaches of Puerto Rico, Vieques,
Culebra, and Saint Croix through Tuesday. Then, the moderate rip
current risk will spread along the north and eastern beaches of
Puerto Rico as well.

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
Issued by National Weather Service Melbourne FL
303 AM AST Tue Jun 3 2025

.KEY MESSAGES...

* Saharan dust will gradually decrease today, while temperatures
remain seasonably warm.

* Even with mostly stable conditions, showers and thunderstorms are
still expected across western Puerto Rico in the afternoon.

* Breezy conditions and choppy seas are expected through much of
the week and in the weekend.

&&

.DISCUSSION...Today (Tuesday) through next Tuesday...

It was a mostly clear, but hazy night across the islands. Rainfall
activity was very limited, with only a few showers over the waters.
Temperatures were warmer than normal, cooling down to the mid and
upper 70s in coastal areas, and near 70s in the mountain. The good
news for today are the dense Saharan Air Layer will gradually
decrease early today, with very low concentrations lingering.

A surface high pressure will maintain the winds out of the east or
slightly northeast, and a little strong too, at 15 to 25 mph, and
stronger gusts. Even though conditions aloft are unfavorable for
strong convection due to the dominance of a high pressure system,
weak perturbations at 700 mb will contribute in the development
of afternoon showers across the interior and western Puerto Rico
each afternoon. Additional quick showers may impact the Virgin
Islands and eastern Puerto Rico too, but the risk of flooding is
very limited.

For a change, temperatures are expected to be a little lower than in
previous days for some areas,but it will be hot regardless, as is
expected for early June. Highs will reach the mid and upper 80s, and
low 90s in some coastal areas. The hottest temperatures are expected
across southern Puerto Rico, from Cabo Rojo to Ponce.

This pattern will stretch into the weekend and early next week,
still with moisture below normal, a little bit of Saharan dust, and
passing showers moving over eastern PR/USVI at times, and
and stronger convection for western PR each day.


&&

.AVIATION...
(06Z) VFR conditions expected to prevail through the forecast
period. VIS will improve around 13Z as HZ from Saharan dust departs.
Winds will be from the E at 16-21 kts, with stronger gusts and sea
breezes variations.

&&

.MARINE...
A surface high pressure over the Atlantic Basin will continue to
promote moderate to locally fresh trade winds over the next few days.
Hazy skies will continue this morning, but visibilities will
gradually improve today. Showers are expected each afternoon along
the western coast of Puerto Rico.

&&

.BEACH FORECAST...
Breezy conditions will continue to result in moderate rip current
risk across portions of northern and southern PR and the USVI today.
The risk will then spread toward eastern and northern PR for the
rest of the workweek.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
Issued by National Weather Service Miami FL
301 AM AST Wed Jun 4 2025

.KEY MESSAGES...

* Breezy conditions will persist for the next couple of days
across the islands.

* Passing showers will move at times across the region, and
stronger showers are expected each afternoon across western
Puerto Rico.

&&

.DISCUSSION...

As the Saharan dust departed the region, a weak disturbance moved
in to the region, bringing a couple of showers over the vicinity
of the Virgin Islands and eastern Puerto Rico. Rainfall
accumulations were not that significant. Temperatures were mostly
in the mid and low 70s in coastal areas.

For the islands, a surface high pressure centered over the eastern
Atlantic will maintain the trade wind enhances, with winds out of
the east at 15 to 20 mph and stronger gusts. The gradient could
tighten by the weekend and early next week, with potential
stronger winds. These trade winds will carry shallow patches of
moisture at times, with passing showers across eastern Puerto
Rico and the Virgin Islands during the day, and across western
Puerto Rico in the afternoon. Rainfall accumulations are not
expected to be too significant, but wet roads and ponding of water
can be anticipated.

Saharan dust will remain minimal, although slight concentrations
of this particulate could approach the region by Sunday and early
next week. Temperatures will remain seasonably warm, with highs in
the upper 80s and low 90s. Heat indices will surpass the 100
degree mark in urban and coastal areas, especially along western
and southern Puerto Rico.

&&

.AVIATION...
(06z) Mostly VFR conditions expected to prevail. SHRA will move at
times across the USVI and TJSJ terminals, with minimal impact to
operations anticipated. After 17Z, SHRA is expected across the
western Cordillera Central, causing mountain obscuration. Winds
are from the E at 15-21 kts, with stronger gusts.

&&

.MARINE...
A building surface high pressure across the central Atlantic will
continue to promote moderate to locally fresh trade winds through
midweek. Small craft should exercise caution across most waters due
to winds exceeding 18 knots through at least late Wednesday. East to
southeast winds are expected during the weekend. Isolated
thunderstorms are expected to develop each afternoon over the western
waters of Puerto Rico. Elsewhere, passing trade wind showers are
expected.

&&

.BEACH FORECAST...
Strong trade winds will maintain a moderate rip current risk
across portions of Puerto Rico and the Virgin Islands. For the
weekend and early next week, these winds might become stronger, so
high rip current risk cannot be ruled out in some areas.