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404
FXCA62 TJSJ 211845
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
245 PM AST Sun Dec 21 2025

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

.KEY MESSAGES...
Issued at 159 PM AST Sun Dec 21 2025

* Cloudiness and passing showers are forecast for the rest of the
  day into the night hours across the northern and eastern sections
  of Puerto Rico.

* Some hazardous marine and coastal conditions will persist as the
  diminishing north-northeasterly swell continues to weaken across
  the local waters.

* For the upcoming week, showers are forecast to increase due to
  moisture from a frontal boundary and an upper-trough. Residents
  can expect frequent light to moderate showers along the north
  coast.

* A cold trend is forecast to start just Wednesday, as winds turn
  from the north-northeast and drier air filters in.

&&

.Short Term(This evening through Tuesday)...
Issued at 159 PM AST Sun Dec 21 2025

Sunny to partly cloudy skies were observed across Puerto Rico and
the U.S. Virgin Islands today. Streamers developed downwind of
the USVI around noon, while low-level cumulus clouds were
developing over the mountain ranges of PR. This surge in low-level
moisture will combine with daytime heating and the sea breeze
convergence to produce showers mainly over west/southwest PR.
Breezy conditions should continue across most coastal areas with
gusts between 25-30 mph. Maximum temperatures were in the mid 80s
along the northern coastal areas and in the upper 80s to low 90s
across the southern areas.

For tonight, a weak induced surface trough will increase showers
across the USVI and eastern half of PR. This activity may lead to
ponding of water in roads and other poor drainage areas. Similar
conditions are expected on Monday and Tuesday, with sunny to
partly cloudy skies prevailing during the day, and showers
developing in the afternoons over west/southwest PR, followed by
passing showers during the night across the USVI and windward
areas of PR. However, moisture content is expected to recover to
around above normal levels briefly on Tuesday afternoon due to an
approaching front from the Atlantic waters. Meanwhile, an upper
level trough will bring colder than normal 500 mb temperatures
late in the period and through midweek. This could lead to
stronger showers and possible isolated thunderstorms.

&&

.Long Term(Wednesday through next Saturday)...
Issued at 411 AM AST Sun Dec 21 2025

The previous forecast remains on track, with Christmas Eve into
Christmas Day expected to be the most active and potentially
unstable period of the long-term forecast. Latest model guidance
continues to indicate mid-level temperatures cooling to below-
normal values, particularly around -10 to -11 degrees Celsius,
which would support somewhat higher instability. This pattern will
be associated with a polar trough extending southward into the
Caribbean, while an additional upper-level trough interacts with a
surface frontal boundary north of the region. This boundary is
forecast to move close to the area or possibly cross the region,
promoting an increase in moisture along with enhanced upper-level
divergence.

Even so, precipitable water (PWAT) values remain near typical levels
for late December, generally around 1.5 to 1.6 inches, or near
the 50th percentile/seasonal normal. With moisture trending closer
to seasonal values, rain chances have been adjusted slightly
downward. Expect a moderate chance (around 50 to 60 percent) for
scattered showers with isolated thunderstorms. At this time,
forecast instability appears limited, favoring mainly shallow
convection with only a few thunderstorms. Overall, model solutions
have been fairly consistent from run to run regarding the
approach of these features. However, uncertainty remains regarding
the exact impacts across Puerto Rico and the U.S. Virgin Islands.

A gradual improvement in weather conditions is expected late in
the workweek into the weekend, as drier-than-normal air and a more
stable pattern become established, leading to generally quieter
conditions. Cooler temperatures are expected to persist through
the holiday weekend, supported by a trend toward below-normal 925
mb temperatures. Any rainfall should be limited, with only low-end
shower chances possible if brief patches of moisture move through.

&&

.AVIATION...
(18Z TAFS)
Issued at 159 PM AST Sun Dec 21 2025

Mainly VFR conditions are expected across all terminals during
the next 24 hours. However, quick passing -SHRA could move at
times across TJSJ and the USVI terminals. Brief MVFR conds are
possible with these trade wind showers. The 21/12z TJSJ sounding
indicated NE winds up to 18 kt blo FL050.

&&

.MARINE...
Issued at 159 PM AST Sun Dec 21 2025

No changes to previous forecasts. Deteriorated marine conditions
persist for the rest of the afternoon hours into the early evening
hours due to a north-northeast swell fading in the local waters.
The latest buoy data from the offshore waters shows seas remain up
to 7 feet. Given the conditions, the small craft advisory is
still in effect for the offshore Atlantic waters and the Anegada
passage until 12 AM AST on Monday. For the rest of the local
waters and seas, waves will remain up to 5 feet. Improving marine
conditions are forecast for Monday morning, just a break until
late Wednesday when another northerly swell moves into the area,
deteriorating marine conditions again for small craft operators.

&&

.BEACH FORECAST...
Issued at 159 PM AST Sun Dec 21 2025

The fading north-easterly swell will continue to result in a high
risk of rip currents across all northern coastal areas, including
Culebra and St. Croix, until late tonight. Coastal conditions will
improve by Tuesday; however, another northerly swell will increase
the risk up to high again by late Wednesday into Thursday.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late tonight for PRZ001-002-005-
     008-012.

VI...High Rip Current Risk through late tonight for VIZ002.

AM...Small Craft Advisory until midnight AST tonight for AMZ711-712-
     716-723.

&&

$$

SHORT TERM...DSR
LONG TERM....MMC
AVIATION...DSR
KEY/BEACH/MARINE...LIS

NWS SJU Office Area Forecast Discussion