National Weather Service Today's Weather Impact Levels

611
FXCA62 TJSJ 200931
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
531 AM AST Sat Dec 20 2025

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

.KEY MESSAGES...
Issued at 531 AM AST Sat Dec 20 2025

* A northeasterly long period swell and increasing northeasterly
  winds will deteriorate marine and coastal conditions during the
  weekend.

* A High Risk of Rip Currents will return this afternoon across the
  northern exposed beaches of Puerto Rico and Culebra, as well as
  eastern St. Croix throughout the weekend.

* A Small Craft Advisory will be in effect this afternoon for the
  offshore Atlantic waters, and then tonight for the Anegada
  Passage, and throughout the weekend.

* Mainly fair weather will persist this weekend with passing showers
  over windward sectors of PR and the USVI, with afternoon showers
  possible mainly over interior to WSW PR.

* Moderate to high rain chances are forecast by mid week next
  week. Residents and visitors are encouraged to stay tuned to the
  forecast updated as there is still uncertainty.

&&

.Short Term(Today through Monday)...
Issued at 531 AM AST Sat Dec 20 2025

Current satellite derived Precipitable Water (PWAT) imagery indicate
patches of moisture with up to 1.45 in, steered by northeasterly
flow, moving in to the region. This has resulted in light to
moderate passing showers over the local waters and moving into the
eastern region. Since midnight, radar accumulations over eastern
Puerto Rico has resulted in up to isolated amounts of around a
quarter on an inch. On the other hand, minimal accumulations were
detected by radar over the USVI. Patchy fog was observed over areas
of the interior. Lows were in the upper 50s and low 60s across
higher elevations of PR, to the upper 60s and mid 70s across lower
elevations of the PR, to the low to mid 70s across lower elevations
of the USVI.

With moderate to fresh northeasterly flow continuing throughout the
period, patches of moisture and drier air will filter into the
region leaving PWAT values at generally normal values for this time
of the year. 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 short term period. This ridge will continue to
provide stability and limit shower development. The ridge will
gradually weaken to end the short term period and into the long term
period as a polar trough starts to exit from eastern CONUS.
Nevertheless, the above mentioned patches of moisture will continue
to bring passing showers with generally minor accumulations over
windward areas of the islands during the morning and overnight
hours. Limited afternoon convection also continues to be possible
each day for mainly west/southwest PR due to local and diurnal
effects. Flooding risks will be limited, with mainly ponding of
water over roadways and poorly drained areas. 925 mb temperatures
will be at seasonal values, highs will be in the mid to upper 80s
across lower elevations of the islands, with isolated/urban areas a
bit higher. Lows will remain similar to tonight, with patchy fog
developing over areas of the interior.

&&

.Long Term(Tuesday through Saturday)...
Issued at 531 AM AST Sat Dec 20 2025

By the beginning of the long term, an upper-level trough tied to
the subtropical jet stream will bring cooler mid-level
temperatures as the mid-level ridge weakens and moves westward.
Patches of low level moisture will continue to move across the
area, resulting in isolated to scattered showers over windward
sections of Puerto Rico and the U.S. Virgin Islands, mainly during
the night and morning hours. By late morning into the afternoon,
a moderate chance of scattered showers, around 50 percent, is
expected across interior and western Puerto Rico with low chances
of flooding concerns.

For Wednesday and Thursday, Christmas Eve and Christmas Day,
atmospheric instability will increase somewhat as 500 mb
temperatures continue to cool further to below normal values
between -8 and -10 degrees Celsius. A polar trough will extend
southward into the Caribbean, while an additional upper-level
trough will interact with a surface frontal boundary north of the
region. The frontal boundary will move close to the area or cross
the region, allowing a slight increase in moisture, while enhanced
upper-level divergence. However, the global models have been
somewhat unstable from run to run, but the latest guidance is now
indicating less available moisture compared to yesterday.
Precipitable water (PWAT) values are trending closer to seasonal
levels, generally around 1.5 to 1.6 inches. Although some
uncertainty remains, the reduction in moisture has led to a slight
downward adjustment in rain chances. A moderate chance (around
50%) is expected for scattered showers with isolated thunderstorms.
Galvez-Davison Index values have also lowered, suggesting reduced
instability and supporting only a few isolated thunderstorms,
with convection remaining mostly shallow.

Friday and Saturday, models are suggesting drier-than-normal air,
leading to stable weather. Cooler temperatures are expected during
the holiday period, as indicated by a trend toward below normal
925 mb temperatures.

&&

.AVIATION...
(06Z TAFS)
Issued at 531 AM AST Sat Dec 20 2025

VFR conditions prevailing during the period. Passing -SHRA at or in
the VCTY of TJBQ/TJSJ/TIST/TISX to start the period. -SHRA/SHRA then
forming over interior to WSW PR, near TJPS/TJBQ, by 20/17 - 23Z.
Winds picking up again from the ENE after 10/13Z  will be calm to
light and variable through this morning, then will return from the
ENE after 19/13z at 15 - 20 kts, with higher gusts and sea breeze
variations.

&&

.MARINE...
Issued at 531 AM AST Sat Dec 20 2025

Moderate to locally fresh east to northeast winds will continue
for the next few days. A long-period northerly to northeasterly
swell, generated by a surface low over the central Atlantic, will
promote hazardous seas for small craft from this afternoon through
at least late Sunday, particularly across the Atlantic waters and
Anegada passage. Small Craft Advisories are in effect from noon
today due to seas gradually building up to 7 feet.

&&

.BEACH FORECAST...
Issued at 531 AM AST Sat Dec 20 2025

Today, there is a moderate risk of rip currents along the north-
facing beaches of Puerto Rico and the U.S. Virgin Islands. A
moderate risk means that life-threatening rip currents are
possible within the surf zone. This afternoon, the risk is
expected to increase to high as beach conditions deteriorate due
to strengthening winds and another northerly swell spreading
across the local Atlantic waters, leading to large breaking waves.
The high risk will likely extend throughout the entire weekend.
Beachgoers are urged to strictly follow guidance from lifeguards,
beach patrol flags, and posted signs. Stay tuned to the forecast
and exercise caution at the beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from this evening through late Sunday
     night for PRZ001-002-005-008-012.

VI...High Rip Current Risk from this evening through late Sunday
     night for VIZ002.

AM...Small Craft Advisory from noon today to 6 PM AST Sunday for
     AMZ711.

     Small Craft Advisory from 6 PM this evening to 6 PM AST Sunday
     for AMZ723.

&&

$$

SHORT TERM/AVIATION...MRR
LONG TERM...YZR

NWS SJU Office Area Forecast Discussion