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875
FXCA62 TJSJ 011859
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
259 PM AST Thu Jan 1 2026

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

.KEY MESSAGES...
Issued at 236 PM AST Thu Jan 1 2026

* Unsettled and wet weather continues through Friday, with
  moderate to heavy rain and isolated thunderstorms. This will
  increase the risk of ponding on roads and localized urban and
  small-stream flooding, especially across western and interior
  Puerto Rico.

* Conditions briefly improve late Saturday into Sunday, with
  fewer showers and more stable weather, offering temporary relief
  from rainfall impacts.

* Across the US Virgin Islands, most activity remains north over
  the Atlantic, with generally calmer conditions and only brief
  passing showers expected.

* Another wet pattern is expected late Monday into Tuesday as a
  cold front approaches, bringing slow-moving showers, isolated
  thunderstorms, and localized flooding risk.

&&

.SHORT TERM (Tonight through Saturday)...

Issued at 236 PM AST Thu Jan 1 2026

On New Year`s Day, the US Virgin Islands and Puerto Rico
experienced tranquil weather, with pleasant winter tropical
temperatures under cloudy skies, due to the proximity of a mid- to
upper-level trough and a frontal boundary. Cloud cover began to
slowly decrease in the afternoon, allowing temperatures to rise
into the mid- to upper 80s along the coast. Winds were mainly from
east-southeast at around 10 mph.

The US Virgin Islands and Puerto Rico observed tranquil weather
conditions with pleasant winter tropical temperatures through the
morning. Cloud cover began to slowly increase from the west across
the islands by mid-morning as an approaching mid- to upper-level
trough moved closer to the region. Additionally, the Doppler Radar
briefly detected some showers affecting the southeast coast of
PR. Winds were mainly from east-southeast at less than 10 mph.

A mid- to upper-level trough will continue to influence the
northeastern Caribbean tonight through Friday, maintaining 500 mb
temperatures between -8 degrees C and -10 degrees C. Combined with
persistently steep lapse rates and above-normal moisture (Total
Precipitable Water near or above the 75th percentile), this
pattern will support instability and favorable conditions for
convective development. A limiting factor for widespread activity
is the cloud cover observed over the region, although satellite
imagery showed some areas with clearing or less sky cover.

From this afternoon through Friday afternoon, there is a 3050%
chance of widespread showers, with localized higher probabilities
(up to 6080%) of heavier rainfall across western and interior
Puerto Rico, and portions of northern Puerto Rico. Isolated
thunderstorms are most likely during the afternoon and evening
hours, particularly over the western half of Puerto Rico, where
low-level convergence and local effects will enhance activity. In
the evening, thunderstorms could develop along the coast, enhanced
by land breeze and low-level convergence. This period carries an
elevated risk of flooding rains, including urban and small-stream
flooding, especially across the interior, western PR, and near the
north coast, where slow-moving showers may develop.

A warming trend aloft begins Friday night and continues into the
weekend, as the trough axis shifts further eastward and mid- to
upper-level stability gradually increases. While showers will
occur at times, primarily due to advection, thunderstorm potential
will decrease noticeably by Saturday, as vertical instability and
upper-level support become less favorable. Overall shower coverage
is expected to decrease on Saturday, with more passing showers
rather than widespread convection.

&&

.Long Term(Sunday through next Wednesday)...
Issued at 236 PM AST Thu Jan 1 2026

The long-term forecast period will begin in the wake of the previous
polar trough passage, with conditions trending toward a more
seasonable pattern across the northeastern Caribbean. At the onset
of the period, near-normal to slightly above-normal moisture is
expected across the region, while weak mid- to upper-level ridging
briefly establishes aloft. Low-level east-southeast flow will
dominate, maintaining generally benign conditions with limited
convective activity.

This relative lull will be short-lived. By late Monday into Tuesday,
another amplifying polar trough is forecast to dig southeastward
into the northeastern Caribbean. As this system approaches, upper-
level dynamics will once again become increasingly favorable for
convective development. Model guidance suggests the development of a
75-90 kt jet streak near the 250 mb level, enhancing upper-level
divergence and ventilation over the region.

At the lower levels, an associated frontal boundary is expected to
approach from the northwest, promoting moisture convergence across
the local area. Precipitable water values are forecast to increase
to above climatological normals, resulting in a deepening moist
column. As a result, a renewed period of unsettled and wet weather
is anticipated across the northeastern Caribbean, with increasing
coverage of showers and isolated thunderstorms.

Considerable uncertainty remains regarding the exact placement of
the most active region and organized convection. However, as the
frontal boundary nears, surface winds are expected to weaken and
become more variable. This may favor slower-moving showers and
thunderstorms, increasing the potential for locally heavy rainfall
accumulations and urban and small-stream flooding.

Following the passage of the polar trough and its associated frontal
boundary late Tuesday into Wednesday, a drier and more stable air
mass is expected to overspread the region. Subsidence aloft and
decreasing moisture will lead to a gradual reduction in shower and
thunderstorm activity through the latter portion of the forecast
period. Trade winds are forecast to reestablish, maintaining more
stable conditions and a reduced risk of convective development by
Wednesday into Thursday.

&&

.AVIATION...
(18Z TAFS)
Issued at 236 PM AST Thu Jan 1 2026

VFR conditions are expected to prevail for most of the period.
Brief MVFR conditions are possible due to temporary reductions in
ceilings and visibility associated with increased cloud cover,
passing SHRA, and isolated TSRA through 01/22Z, and tomorrow
between 02/17-022z. Surface winds from the east to east-southeast
at 1015 kt, with occasional higher gusts and sea breeze
influences, becoming calm to light and variable after 01/23z.
Winds will return from the E-ENE at around 10 kt with sea breeze
variations after 02/13z.

&&

.MARINE...
Issued at 236 PM AST Thu Jan 1 2026

A frontal boundary approaching the northeastern Caribbean will
promote a moderate east-southeast wind flow across the region
through at least Friday. Then, as the front interacts with a
surface high pressure building over the central Atlantic, winds
will return from the east to northeast Friday into the weekend.
Additionally, a long-period northerly swell will slowly dissipate
across the local waters through late tonight. Also, frontal
proximity will support the development of showers and
thunderstorms, especially across the Mona Passage and Atlantic
Waters through at least Friday.

&&

.BEACH FORECAST...
Issued at 236 PM AST Thu Jan 1 2026

Beachgoers, although surf zone conditions have improved, please
exercise caution as there is still a moderate risk of observing
life-threatening rip currents, especially from Rincon along the
Atlantic Coastline to Fajardo, Culebra, Vieques, St Croix, St
Thomas, St John, and the Adjacent Islands.

There is a limited to elevated chance of lightning across the
western and northern beaches of Puerto Rico, particularly this
evening and again on Friday afternoon. Remember that lightning can
strike several miles away from a thunderstorm. If you hear
thunder, seek shelter immediately.

&&

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

$$

DAY SHIFT...CAM/GRS
EVENING SHIFT...DS/MRR

NWS SJU Office Area Forecast Discussion