National Weather Service San Juan PR
419 AM AST Tue Jan 23 2024
.SYNOPSIS...
Today, expect stable weather conditions across Puerto Rico and
U.S. Virgin Islands. Along with the stable weather, there is a
elevated risk for fire weather conditions across Puerto Rico.
Therefore, we urge the public, fire, and emergency officials to
be aware of the weather conditions and surroundings. Breezy
easterly winds will prevail through the rest of the week, as
surface high pressure ridging dominates the western Atlantic. A
cold front will approach the islands by midweek, increasing the
frequency of showers. Marine and coastal conditions will be
deteriorated all week due to ongoing winds and the presence of a
northerly swell.
&&
.SHORT TERM...Today through Thursday...
An analysis of overnight radar and satellite imagery indicated that
most of the region mainly remained rain- and cloud-free, except for
windward areas of eastern and northern Puerto Rico and the US Virgin
Islands, where pockets of low-level moisture generated partly to
variably cloudy skies and passing showers after midnight. Overnight
temperatures from official reporting sites ranged from around 60
degrees in higher elevations to about 75 degrees across eastern
Puerto Rico and the local islands. Winds were generally light from
the east to east-northeast across windward areas but calm and
variable elsewhere.
Today, the weather will likely remain stable, with an airmass
exhibiting notably lower-than-average moisture levels (as low as 0.8
inches) streaming over the region, indicated by satellite-derived
precipitable water. This scenario is coupled with a strong trade
wind cap inversion supported by a persistent mid-level ridge,
creating conditions unfavorable for deep convective development.
However, there is a chance for increased cloud cover and shower
development on Wednesday, attributed to a significant rise in
moisture levels to as high as 1.7 inches, exceeding two standard
deviations from typical seasonal values, as the remnants of an old
frontal boundary reach the area. While the focus of activity will
likely favor the eastern half of Puerto Rico and the local islands,
other areas may also experience some shower activity. However, the
likelihood of flooding impacts is limited, primarily attributed to
the rapid movement of showers. Rainfall amounts will likely remain
around half to three-quarters of an inch with the most frequent
activity, possibly generating ponding of water on roadways and
poorly drained areas.
On Thursday, another dry air mass is forecasted to move over the
region, with precipitable water values dropping two standard
deviations below typical seasonal values (around 0.9 inches).
Consequently, stable weather conditions are anticipated to return on
Thursday.
The general forecast features temperatures at 925 mbar cooler than
the norm and consistently higher-than-average wind speeds throughout
the period. Today and Thursday are anticipated to have mainly sunny
to clear skies, while Wednesday is expected to bring variable skies
and showery conditions. Daytime high temperatures will likely stay
in the mid 80s today and lower to mid 80s on Wednesday and Thursday,
accompanied by east to east-northeast winds at 15-25 mph with higher
gusts.
&&
.LONG TERM...Friday through Tuesday...
On Friday, the surface high-pressure system over the western Atlantic
will continue to develop and move over the central Atlantic. The
latest model guidance suggests precipitable water values in the
25th percentile/below normal climatological values across Puerto
Rico and the U.S. Virgin Islands. By the beginning of the
workweek, the ridge at the mid-upper levels will weaken and move
to the west of the forecast area, allowing mid to upper-level
troughing to position close to the region. As the troughing and
surface high pressure prevail, additional patches of moisture from
an old frontal band will be pushed across the islands, allowing
some showery weather at times during the weekend. The mid to upper
trough will allow surface moisture to reach the mid-levels,
enhancing the vertical development of rainfall activity along with
some unstable conditions across the islands. At this time, model
guidances suggest Monday and Tuesday as the best days for rainfall
activity, along with some unstable weather conditions across
Puerto Rico and the U.S. Virgin Islands. The latest guidance shows
an upper-level jet maxima of 50 knots and PW values above-normal
climatological values (around 2 inches)on Monday.
&&
.AVIATION...
(06Z TAFS)
VFR conditions will prevail across all terminals, with increased
SHRA after 23/22Z for TJSJ and USVI terminals. Thus, brief MVFR
conditions are possible with minimal impact on operations. E to
ENE wind at 5-15 knots, increasing to 15-20 knots with gusts up to
25-30 knots between 23/14-23Z. Wind speeds will fall back to 5-15
knots after 23/23Z, but gusty near SHRA.
&&
.MARINE...
A broad surface high pressure ridge building in the western Atlantic
will continue to promote deteriorating seas from today onwards due
to increasing easterly winds combining with the arrival of a
northerly swell. A weak frontal boundary is forecast to sink
southwards across the regional waters by Wednesday as the surface
high pressure prevails across the western Atlantic. Therefore, the
moderate to fresh easterly winds will continue thus prolonging
hazardous marine conditions.
&&
.BEACH...
A high risk of rip currents will exist across most of the local
beaches throughout the week due to breaking waves between 6-8
feet. Southern Puerto Rico is the exception with breaking waves
around 5 feet.
&&
.FIRE WEATHER...
A persistent air mass characterized by lower-than-normal moisture
content, breezy to windy conditions, continuous abnormally dry to
moderate drought conditions, significantly dry soils, and
available fuels will support an elevated fire danger risk across
Puerto Rico today. Overall, the forecast features clear to partly
cloudy skies, with high temperatures reaching the mid to upper
80s, minimum relative humidity falling into the mid-40s to mid-
50s, peak wind speeds within the 15-25 mph range, and gusts up to
30- 35 mph. The previous KBDI reading in Guanica was recorded at
672, while in Cabo Rojo, it was 451. Overall, this scenario will
favor the spread of any brush and grassland wildfires,
particularly across fire-prone areas of southern Puerto Rico.