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252
FXCA62 TJSJ 120918
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
518 AM AST Fri Dec 12 2025

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 409 AM AST Fri Dec 12 2025

* Choppy to rough seas and life-threatening rip currents are
  expected to continue through the weekend.

* For Puerto Rico, passing showers are expected mainly during the
  night/early morning hours across coastal areas of eastern,
  southern, and northern PR, followed by afternoon shower activity
  over the western PR.

* For the U.S. Virgin Islands, fair weather conditions expected
  through the morning hours. Passing showers increasing once again
  later tonight through Saturday.

&&

.Short Term(Today through Sunday)...
Issued at 409 AM AST Fri Dec 12 2025

Isolated to scattered showers associated with a disturbance
persisted during the night, moving across the local waters and
portions of southern and eastern Puerto Rico, as well as the U.S.
Virgin Islands.  Based on the WSR-88D rainfall estimates, these
areas received up to 1 inch of precipitation. By midnight, isolated
thunderstorms developed over the Mona Passage, producing lightning.
Temperatures were slightly warmer than yesterday, as cloud cover
inhibited effective radiative cooling, and stations reported less
widespread cooler temperatures. Over coastal areas, temperatures
remain in the mid-70s, while higher elevations stayed in the mid to
high 60s, with isolated areas dropping to the low 60s. Stronger
winds were seen last night, as more stations in coastal areas and
higher elevations reported wind gusts up to 27 mph.

Small changes were introduced to the short-term forecast, as
variable conditions are likely to persist in the weekend. As the
disturbance continues to retreat from the region, satellite-derived
products show the drier air mass mentioned in the previous
discussion already started filtering into the region, bringing
mostly fair conditions across the CWA. Based on the latest model
solutions, low to mid level moisture content should plummet to below
climatological normal ( with PWAT values between 1.0 and 1.2 inches,
even lower), which should limit the shower activity for today. The
surface high pressure will strengthen and linger over the Central
Atlantic throughout the period, with east-southeasterly winds
increasing, leading to breezy to windy conditions across the
islands. The mid-level ridge northeast of the region is now expected
to weaken due to a polar trough deepening into the tropics, which
will slightly cool 500 mb temperatures (between -6 and -7 degrees
Celsius), promote cloud growth, and introduce marginal instability
across the CWA. Confidence is increasing in the short term, as
deterministic guidance of the GFS and ECMWF currently agrees on an
increase of moisture content due to a disturbance in the trades
moving across the region tonight, and another on Saturday evening
into early Sunday. Ensemble members are now tending to a wetter
pattern for this time of the year, with PWAT values likely between
1.4 and 1.6 inches, a medium to high chance of reaching 1.8 inches
on Saturday night (above climatological normal). The most likely
scenario remains, with an increase in shower activity, particularly
across the U.S. Virgin Islands and the eastern half of Puerto Rico,
becoming stronger on Saturday evening. Although showers and isolatd
thunderstorms will likely be progressive rather than stationary,
periods of heavy showers will likely lead to ponding of water along
roads and poorly drained areas, with isolated urban and small
streams flooding. Hence, the flooding risk will remain limited,
particularly over northeastern Puerto Rico, including Vieques and
Culebra, and St. Thomas and St. John in the U.S. Virgin Islands.
Weather conditions should improve by Sunday morning, as another
drier air mass will reduce moisture content in the low and mid
levels, enhancing stability across the CWA and limiting shower
activity. As mentioned in the previous discussion, a southeasterly
wind pattern will continue pooling warmer air, leading to above
climatological normal temperatures in the short term. Nevertheless,
the heat threat will remain low for the rest of the period.


&&

.Long Term(Monday through Friday)...
Issued at 409 AM AST Fri Dec 12 2025

Global models have a wetter solution than previous days with the
approaching frontal system over the western Atlantic and
associated upper level trough promoting more unstable conditions
through first part of the workweek. The 500 mb temperatures are
expected to drop to around -6.5C and the precipitable water
content is expected to remain near 1.75 inches, above normal
levels for most of the period. The mid-to upper-level ridge is now
expected to erode earlier and have little influence in the local
weather conditions. Pooling of normal to above normal moisture
content over the area will lead to weak surface troughs to move
from the east on most days, increasing the chance of showers
between 50-70% each day across the islands, with a slight chance
of thunderstorm development over western PR in the afternoon
hours. However, decided to not include them in the forecast as of
now due to possible model variations.

At the surface, a broad high pressure will linger near and south
of the Azores through the long term period. Meanwhile, a cold
front over the western Atlantic should remain north of the region
early in the forecast. This will promote a southeasterly wind
flow, leading to warmer than normal temperatures before the onset
of afternoon showers. Another surface high pressure is expected to
build behind the front and over the western Atlantic during the
second part of the week, bringing east to northeast trades and
a cooler air mass.

&&

.AVIATION...
(06Z TAFS)
Issued at 409 AM AST Fri Dec 12 2025

Mainly VFR conds are expcd across most TAF sites, with VCSH due SHRA
associated to disturbance through at least 12/12z. Winds from the E-
SE will increase by 12/13-14z, around 15 kt with gusts up to 25 kt
through 12/23z. VFR conds will return in the morning as a drier ams
will move across the CWA, reducing SHRA activity, returning after
12/22-23z. VCSH for most terminals, that may reduce CIGs/VIS and
lead to brf MVFR conds.

&&

.MARINE...
Issued at 409 AM AST Fri Dec 12 2025

A surface high pressure will continue to build near the Azores
through the weekend. A weak cold front and another surface high
pressure will move from the western Atlantic into the central
Atlantic during the next few days. This will promote moderate to
locally fresh east to southeast trades across the local waters.
Increasing winds and a long period northerly swell will cause choppy
to rough seas, mostly across the Atlantic waters and portions of
the Anegada and Mona Passages.

&&

.BEACH FORECAST...
Issued at 409 AM AST Fri Dec 12 2025

A long period northerly swell and increasing wind-waves will
cause life-threatening rip currents along the north and east
facing beaches of the islands during the next few days. There is a
Rip Current Statement in effect for the northwest to northeast
beaches of PR, including Culebra, and the northern USVI. Beach
goers are urged to avoid swimming in these conditions, particularly
today and on Friday. The west/southern beaches of the islands
will have a moderate risk of rip currents.

&&

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

     High Rip Current Risk through late tonight for PRZ012.

VI...High Rip Current Risk through late tonight for VIZ001.

AM...Small Craft Advisory until 5 PM AST Sunday for AMZ711.

     Small Craft Advisory until 6 PM AST this evening for AMZ712-716.

     Small Craft Advisory until noon AST Saturday for AMZ723.

     Small Craft Advisory until midnight AST tonight for AMZ741.

&&

$$

SHORT TERM...MRR
LONG TERM....DS
AVIATION...MNG

NWS SJU Office Area Forecast Discussion