Your Number One Source for Real-Time Puerto Rico Weather & Hurricane Tracking Updates

454
FXCA62 TJSJ 030903
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
503 AM AST Sat Jan 3 2026

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

.KEY MESSAGES...
Issued at 449 AM AST Sat Jan 3 2026

* For Puerto Rico, afternoon showers could lead to ponding of
  water over roads and localized urban and small-stream flooding,
  mainly across Puerto Rico`s mountain areas.

* For the US Virgin Islands, passing showers are expected
  throughout the day, leading to puddles over the road and brief
  periods of heavy rainfall.

* Unsettle weather conditions will likely return by Three Kings
  Eve, increasing potential of showers and isolated thunderstorms
  across the region and enhance flooding and lightning risk.
  Residents and visitors are urged to stay tuned for further
  updates.

&&

.Short Term(Today through Monday)...
Issued at 449 AM AST Sat Jan 3 2026

Lingering low- to mid-level moisture combined with weak troughing
aloft will continue to influence weather conditions across Puerto
Rico and the U.S. Virgin Islands through the short-term period.
Under an east-to-east-southeasterly low-level flow, isolated to
scattered showers are expected during the morning hours across
windward coastal areas, followed by afternoon convection over
interior and western to northwestern Puerto Rico driven by diurnal
heating and local effects. With slightly less cloud cover compared
to previous days, diurnal heating will likely play a larger role
today, enhancing convective development during the afternoon hours,
although activity should remain shallow overall.

By Sunday, conditions are expected to become more stable as ridging
aloft briefly establishes over the region. Precipitable water values
will decrease to near-climatological levels, resulting in reduced
overall shower coverage. While some passing showers will still be
possible, particularly during the early morning hours, Sunday is
expected to be the quietest day of the period.

Conditions will become increasingly unstable late Sunday into Monday
as another polar trough approaches from the northwest, bringing
cooler temperatures at 500 mb and improved upper-level divergence
across the region. This trough appears more favorably positioned
than the previous system, resulting in enhanced upper-level
ventilation and increasing mid-level lapse rates. At the surface, a
pre-frontal boundary is forecast to move across the area on Monday,
while a col develops over the northeastern Caribbean, leading to
weakened steering wind flow and enhanced low-level moisture
convergence.

With ample columnar moisture, cooling aloft, and weak low-level
winds, an active convective pattern is expected on Monday afternoon.
Slow-moving showers and thunderstorms may develop across interior
sections of Puerto Rico, increasing the potential for locally heavy
rainfall. As convective outflows propagate outward, activity may
spread toward coastal areas later in the afternoon and evening.
Additionally, given that the primary trough axis remains just north
of Puerto Rico and the U.S. Virgin Islands, repeated redevelopment
of showers and thunderstorms over the Atlantic waters is possible,
with some activity occasionally impacting near-shore areas.

Potential impacts include localized urban and small-stream flooding,
particularly where slow-moving convection persists or where repeated
thunderstorms affect the same locations. While widespread flooding
is not anticipated at this time, residents and visitors are urged to
remain attentive to weather conditions and future updates.

&&

.Long Term(Tuesday through Saturday)...
Issued at 449 AM AST Sat Jan 3 2026

The long-term forecast remains on track, transitioning from an
unsettled weather pattern into more stable conditions. Tuesday is
expected to be the wettest day of the period, as the latest model
guidance continues to suggest the presence of the polar trough and
remaining moisture in the early morning. From the deterministic
guidance of the GFS and ECMWF, PWAT values will likely stay between
1.4 and 1.6 inches (with a lower chance of reaching 1.8 inches),
being above climatological normal.  In terms of instability, the CWA
will likely be positioned on the favorable side of the trough for
deep convection (eastern half of Puerto Rico and the U.S. Virgin
Islands. From the latest model guidance, factors include cooler-than-
normal 500 mb temperatures (between -10 and -9 Celsius), strong
upper-level winds (60 - 80 kt), and upper-level divergence allowing
rising air, cloud growth, and ventilation aloft, which leads to the
development of thunderstorms.  As mentioned in the previous
discussion, the most likely scenario on Tuesday (Three Kings Day)
will likely rely on an advective cooling pattern in the early hours,
with showers and isolated thunderstorms moving across the local
Atlantic waters into portions of eastern Puerto Rico and the U.S.
Virgin Islands. Although winds are expected to increase as a col
region moves away from the CWA during the day, showers and
thunderstorms may become stationary and produce heavy rainfall in
localized areas. Afternoon convection remains uncertain, as a drier
air mass is expected to arrive during the day and may inhibit shower
and thunderstorm activity. Therefore, the flooding and lightning
risk will remain limited over the aforementioned areas, with mainly
ponding of waters over roads, urban, and poorly drained areas, with
localized flooding.

As the polar trough moves away from the region and the surface high
pressure builds over the western Atlantic, winds will remain from
the NE-ENE for the rest of the period. Drier and most stable air
will continue to filter into the region, with PWAT values dropping
to well below normal (between 0.9 - 1.1 inches). Additionally, a mid-
level ridge is expected to linger over the northern Caribbean,
slightly warming mid-level temperatures (around - 8 degrees Celsius)
and promoting stability aloft. Patches of moisture are likely to
move across the local area by Thursday, bringing showers across
windward sections in the morning hours and increasing the chance of
afternoon convection. Nevertheless, rainfall accumulations are
likely to remain minimal, with no risk of flooding. Once again,
drier air should filter into the region, limiting shower activity.

The latest model solutions are now suggesting slightly warmer 925 mb
temperatures, as the wind pattern is tending more from the ENE.
Nevertheless, seasonal to below normal temperatures are very likely
in the long term forecast, with coastal areas and lower elevations
in the low to mid 70s, while higher elevations in the 60s, with
localized areas dropping to the upper 50s.

&&

.AVIATION...
(06Z TAFS)
Issued at 449 AM AST Sat Jan 3 2026

VFR expected at all TAF sites. VCSH/SHRA possible at times, mainly
AM over windward terminals and PM over interior and
western/northwestern PR due to local effects. Brief MVFR possible in
passing showers. Winds E-ESE 08-13 kt aft 13z with sea breeze
variations, becoming light and VRB overnight aft 23z.

&&

.MARINE...
Issued at 449 AM AST Sat Jan 3 2026

As a surface high pressure builds across the Central Atlantic into
the northeast Caribbean, winds will continue light to moderate out
from the east to east-southeast through at least early next week.
Another frontal boundary and polar trough will approach the local
area by following Monday, promoting light northeast to northerly
winds and an increasing potential for showers and thunderstorms
early next week. A small northerly swell will arrive around late
Saturday into Sunday, and another pulse with longer period from
the northeast by the middle of next week.

&&

.BEACH FORECAST...
Issued at 449 AM AST Sat Jan 3 2026

A small northerly swell is expected to arrive late tonight into
Sunday and spread across the local waters and passages. Hence, the
risk of rip currents will remain moderate along northern and east-
facing beaches of Puerto Rico, including Culebra, and St. Thomas and
St. John in the U.S. Virgin Islands. Although a high risk is not
expected, beachgoers are encouraged to exercise caution, and life-
threatening rip currents are possible along these beaches. The risk
will likely be low along most beaches of Puerto Rico and the U.S.
Virgin Islands on Monday due to weakening winds, though it is
expected to become moderate on Tuesday. A long-period northeasterly
swell is still forecast to arrive by mid week, producing life-
threatening rip currents and leading to hazardous conditions along
exposed beaches. Beachgoers are urged to stay tuned to the latest
updates of the beach forecast.

Due to the expected weather conditions early next week, beachgoers
are encouraged to stay weather alert due to shower and thunderstorm
activity likely to develop near coastal areas of northern Puerto
Rico and the U.S. Virgin Islands, increasing the lightning risk.
Seek shelter whenever you hear thunder.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION...CVB
LONG TERM/MARINE...MNG

NWS SJU Office Area Forecast Discussion