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966
FXCA62 TJSJ 210904
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
504 AM AST Sun Dec 21 2025

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

.KEY MESSAGES...
Issued at 411 AM AST Sun Dec 21 2025

* A fading northeasterly long period swell will continue to result
  in deteriorated marine and coastal conditions today and tonight.
  Another stronger northerly swell will again deteriorate marine and
  coastal conditions Tuesday through at least the rest of the
  workweek.

* A High Risk of Rip Currents continues for the northern exposed
  beaches of Puerto Rico and Culebra, as well as eastern St. Croix,
  through 6 AM AST Monday. These conditions then return by around
  late Tuesday.

* A Small Craft Advisory continues for the Atlantic waters and the
  Anegada Passage until at least midnight tonight. These conditions
  then return by around Tuesday.

* Light to moderate passing showers under northeasterly winds will
  continue across windward sectors of PR and the USVI today,
  afternoon showers then forecast for interior to SW PR.

* For the Christmas Eve into Christmas Day, a wet and unstable
  weather pattern is forecast with a moderate to high chance of
  widespread showers and thunderstorms. Residents and visitors of
  Puerto Rico and the US Virgin Islands are urged to stay tuned
  for further updates in the forecast.

&&

.Short Term(Today through Tuesday)...
Issued at 411 AM AST Sun Dec 21 2025

Current satellite derived Precipitable Water (PWAT) imagery indicate
patches of moisture with up to 1.60 in, steered by northeasterly
flow, moving mainly around St. Croix. Other coastal areas currently
have PWAT values of around 1.30 to 1.40 in. Light to moderate
passing showers over the local waters have continued, moving into
coastal windward areas. SInce midnight, radar estimated
accumulations over eastern Puerto Rico have resulted in up to
isolated amounts of around 0.40 in. Radar estimated accumulations
were also detected over Culebra, Vieques, the USVI, north-central PR
and southeastern PR. Patchy fog was also observed over areas of the
interior. Minimum temperatures were in the upper 50s to low 60s
across higher elevations of PR, in the upper 60s and mid 70s across
lower elevations of PR, and in the low to mid 70s across the USVI.

A series of surface highs and frontal lows over the Atlantic will
result in northeasterly steering flow through most of the period.
This will bring in patches of moisture and passing showers embedded
in the trade winds towards windward sectors, resulting in generally
seasonal PWAT values. This available moisture will mostly be
confined to the lower levels, as a mid to upper level ridge
continues over the region to start the week. This ridge will
continue to provide stability and limit vertical shower development.
500 mb temperatures will be warmer than normal, but will gradually
decrease as the period progresses. The ridge will gradually weaken
as the short term period progresses as a polar trough moves over the
western Atlantic late tonight and continues moving east as the
period progresses. 500 mb temperatures will be colder than normal by
Tuesday. Patches of moisture and passing showers with generally
minor accumulations will continue to be steered over windward areas
of the islands during the period, mainly during the morning and
overnight hours. Limited afternoon convection is also forecast each
day for mainly west/southwest PR due to sea breeze convergence and
diurnal hearing. Heavier showers can result in ponding of water over
roadways and poorly drained areas. 925 mb temperatures will be at
seasonal values but with a slight cooling trend as the period
progresses. Maximum temperatures will be in the mid to upper 80s
across lower elevations of the islands, with isolated/urban areas a
bit higher. Minimum temperatures will remain similar to tonight,
with patchy fog also developing over areas of the interior during
the overnight hours.

&&

.Long Term(Wednesday through Sunday)...
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...
(06Z TAFS)
Issued at 411 AM AST Sun Dec 21 2025

Mainly VFR conditions across the terminals. Passing -SHRA at or in
the VCTY of TJBQ/TJSJ/TIST/TISX with, between 21/17 - 23Z, -SHRA
/SHRA developing over interior to WSW PR that can also reach the
VCTY of TJPS/TJBQ. Winds from the NE after 21/13Z up to 15 to 19
kts, with higher gusts and sea breeze variations.

&&

.MARINE...
Issued at 411 AM AST Sun Dec 21 2025

The moderate to locally fresh east to northeast winds will continue
for the next few days. These winds along with pulses of a fading long-
period northerly to northeasterly swell will promote hazardous
seas for small craft, particularly across the Atlantic waters and
Anegada passage. Small Craft Advisories remain in effect due to
seas gradually building up to 8 feet through this evening. Marine
conditions will briefly improve tonight into Monday, before
another stronger northerly swell promotes hazardous marine
conditions for small craft by late Tuesday into midweek.

&&

.BEACH FORECAST...
Issued at 411 AM AST Sun Dec 21 2025

For the rest of the day, a moderate risk of rip currents will
persist as coastal marine conditions deteriorate with the arrival of
the north-northeasterly swell. Therefore, from 6 PM AST onward,
there is a high risk of rip currents across all northern coastal
areas, including Culebra and St. Croix, until Monday evening.
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 AMZ711-723.

     Small Craft Advisory until midnight AST tonight for AMZ712-716.

&&

$$

SHORT TERM/AVIATION...MRR
LONG TERM/MARINE/BEACH FORECAST...MMC

NWS SJU Office Area Forecast Discussion