232
FXCA62 TJSJ 290912
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
512 AM AST Mon Dec 29 2025

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

.KEY MESSAGES...
Issued at 420 AM AST Mon Dec 29 2025

* Pulses of a fading, long-period northerly swell will continue to
  spread, maintaining a high risk of life-threatening rip currents
  along the north-facing beaches of Puerto Rico, Culebra, St.
  Thomas, and St. John through at least Tuesday afternoon. The risk
  is expected to remain from low to moderate thereafter.

* Fair weather conditions and cooler than normal temperatures will
  prevail through Tuesday across Puerto Rico and the U.S. Virgin
  Islands.

* An increase in moisture and marginal instability is expected
  from New Years Eve through the end of the week. As a result,
  rain chances are expected to increase across the forecast area.
  Forecast timing uncertainty remains high, continue to monitor
  forecast updates.

&&

.Short Term(Today through Wednesday)...
Issued at 420 AM AST Mon Dec 29 2025

Skies remain mostly clear across much of the area, with some
clouds over the northern U.S. Virgin Islands, where a few isolated
showers were observed earlier. Rainfall has been minimal.
Temperatures have already dropped into the mid-50s across higher
elevations and the low-60s across lower elevations, with many
locations cooler than last night, and may continue to fall a few
degrees as the night progresses. Patchy fog has been reported in a
few areas, including near Mercedita Airport, which may briefly
reduce visibility. Winds are light and variable, helping keep
conditions calm overnight.

A broad surface high over the westerncentral Atlantic will
maintain light to moderate easterly winds, gradually veering
tonight and becoming east-southeasterly on Tuesday. A persistent
mid-level ridge will continue to promote subsidence and relatively
dry conditions, limiting overall shower coverage. Most shower
activity during this period will occur as brief, isolated trade-
wind showers, favoring exposed east-facing coastal areas and the
U.S. Virgin Islands, mainly during the nighttime and early morning
hours. In addition, isolated afternoon convection cannot be ruled
out, primarily over the interior to northwestern Puerto Rico, driven
by local effects. Overall, shower probabilities will remain low
to locally moderate (around 3040 percent), with brief rainfall
and long dry breaks. Temperatures will remain relatively cool
during this period, although it marks the beginning of a subtle
warming trend, and no weather-related hazard risks are expected
across inland areas.

From Tuesday night into Wednesday, weather conditions begin to
change as a short-wave trough approaching from the western
Caribbean allows moisture to increase. Expect scattered to at
times numerous showers on Wednesday, with locally heavy rain
possible, mainly across western and interior Puerto Rico. Isolated
thunderstorms may develop, primarily over the west, though a few
could occur farther east if conditions allow; however, drier air
lingering over eastern Puerto Rico and the U.S. Virgin Islands may
limit thunderstorm development. As a result, flooding and
lightning risks increase during the day, with conditions gradually
improving late Wednesday night as the wetter pattern moves away.
Temperatures will remain on the cool side with a slight warming
trend.

&&

.Long Term(Thursday through Monday)...
Issued at 420 AM AST Mon Dec 29 2025

A shortwave trough is expected to swing across the Northeast
Caribbean by Thursday (New Year`s Day), followed by an amplifying
mid- to upper-level trough over the region through Friday. This
pattern will promote increased instability and a more unsettled
weather regime, especially as a frontal boundary and associated pre-
frontal trough approach the area late Thursday night into Friday. At
the surface, a high-pressure system over the central Atlantic will
maintain an east to east-southeast low-level wind flow through early
next week.

The most favorable window for widespread rainfall appears to be
between Thursday afternoon and Friday evening. However, model
guidance continues to show timing discrepancies regarding both the
onset and departure of the most active period. Rainfall could begin
as early as early Thursday morning and linger into early Saturday
morning. At this time, the highest confidence for widespread shower
activity is from Thursday afternoon into Friday, when periods of
moderate to heavy rain and thunderstorms are most likely. Another
negative factor for the formation of widespread activity could be
the available moisture over the region, where we observed another
discrepancy in the model guidance.

By Saturday, the region will transition to the subsident side of the
mid- to upper-level trough as it lifts eastward, with subsidence
gradually increasing. This will result in a decreasing trend in
shower and thunderstorm coverage and intensity through the weekend.
Although passing showers will remain possible Saturday into Sunday,
vertical development will be limited as a mid- to upper-level ridge
builds over the area.

Late Sunday night into Monday, another shortwave trough is forecast
to approach the region, increasing mid- to upper-level instability.
This may lead to a gradual uptick in shower activity, with the
trough aloft expected to further amplify by Monday night into
Tuesday, potentially signaling a return to more unsettled conditions
early next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 420 AM AST Mon Dec 29 2025

Mainly VFR conds exp at all TAF sites thru 24 hrs. Brief -SHRA and
SCT cigs FL025060 psbl nr USVI sites thru 29/13Z and aft SHRA
near TJPS/TJBQ. Ops impacts mnml. Winds lgt/vrb, bcmg ENE 812 kt
btw 29/1322Z, then lgt/vrb aft 29/22Z.

&&

.MARINE...
Issued at 420 AM AST Mon Dec 29 2025

A surface high-pressure moving eastward from the Western to Central
Atlantic, interacting with the remnants of an old frontal boundary,
will create light easterly wind flow across the region through
Tuesday. By midweek, an eastward-moving frontal boundary and a high-
pressure system building across the Central Atlantic will lead to a
moderate east-to-east-southeast wind flow, increasing the chance of
showers and thunderstorms. Pulses of long-period northerly swells
will also continue to spread across the Atlantic Waters and Caribbean
Passages through the middle of the week. Small craft operators
should exercise caution, especially in exposed Atlantic waters and
Caribbean passages.

&&

.BEACH FORECAST...
Issued at 420 AM AST Mon Dec 29 2025

Pulses of a fading, long-period northerly swell will continue to
spread across the local waters, maintaining a high risk of life-
threatening rip currents along the north-facing beaches of Puerto
Rico, Culebra, St. Thomas, and St. John through at least Tuesday
afternoon. As a result, a Rip Current Statement remains in effect
through that period. A low to moderate rip current risk is expected
from midweek through the weekend. Even when the rip current risk is
low, life-threatening rip currents can still occur near groins,
jetties, reefs, and piers. Beachgoers should exercise caution at all
times.
&&

.FIRE WEATHER...
Issued at 420 AM AST Mon Dec 29 2025

Drying conditions continue, especially across southern Puerto
Rico, where minimum relative humidity has fallen below 40% for a
second consecutive day, with some locations dropping into the 20s
to 30s. Winds remain light, limiting fire spread at this time.
KBDI values continue to increase, with Cabo Rojo exceeding fire
danger thresholds (above 550) and Camp Santiago approaching
similar levels, indicating increasingly dry fuels. While no
significant fire weather threat is expected today, continued
drying through mid to late week warrants close monitoring,
particularly as stronger winds are possible Friday into Saturday,
which could elevate fire spread potential if dry conditions
persist.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Tuesday afternoon for PRZ001-002-
     005-008-010-012.

VI...High Rip Current Risk through Tuesday afternoon for VIZ001.

AM...None.
&&

$$

SHORT TERM...ICP
LONG TERM....CAM
AVIATION...ICP

NWS SJU Office Area Forecast Discussion