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132
FXCA62 TJSJ 031736
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
136 PM AST Sat Jan 3 2026

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

.KEY MESSAGES...
Issued at 1259 PM AST Sat Jan 3 2026

* Localized flooding is possible this afternoon, mainly across
  interior and western Puerto Rico, where periods of moderate to
  locally heavy rain may cause ponding on roads and in poorly
  drained areas, with isolated urban and small-stream flooding.
  Similar ponding is also possible across eastern Puerto Rico,
  including the San Juan metro area, and across parts of the US
  Virgin Islands if showers move inland in the afternoon or
  evening.

* Flooding rains are more likely Monday afternoon into the
  evening, especially across the northern half of Puerto Rico,
  where an elevated risk of flooding exists along with a limited
  risk of thunderstorms. Conditions across the US Virgin Islands
  remain uncertain at this time; stay tuned for forecast updates.

* Beach hazards will continue through early next week, with a
  moderate rip current risk along northern and east-facing beaches
  through Sunday. Hazardous conditions are expected to increase
  by Tuesday with the arrival of a longer-period northeasterly
  swell.

&&

.Short Term(This evening through Monday)...
Issued at 1259 PM AST Sat Jan 3 2026

Calm weather conditions prevailed across the islands today. Clear
skies were observed early in the morning, with little or no rain.
After mid-morning and into early afternoon, showers began to
increase across the waters and downwind of the USVI, occasionally
moving across eastern PR, including the San Juan Metro area.
Temperatures ranged from the mid to upper 80s along the coast to
the upper 70s in the mountains. Winds were from the east-southeast
at 5 to 15 mph.

A ridge pattern at the mid and upper levels of the atmosphere will
be in place from tonight through Sunday. This pattern is
associated with dry air and subsidence aloft, which generally
limits widespread rainfall during this period. At the surface,
high pressure across the central Atlantic will maintain an east to
east-southeast wind flow through the weekend.

This afternoon and evening, a patch of moisture moving into the
region will interact with local effects and sea breeze variations.
This will promote periods of showers, particularly across the
interior and western portions of Puerto Rico, as well as
surrounding waters and portions of the US Virgin Islands. These
showers may produce moderate to locally heavy rainfall. As a
result, there is a limited risk of excessive rain today, which
could lead to ponding of water on roads and in poorly drained
areas, along with isolated urban and small-stream flooding across
interior and western Puerto Rico. Similar ponding of water is also
possible across eastern Puerto Rico, including areas downwind of
El Yunque into the San Juan metropolitan area. If showers move
inland across the US Virgin Islands, ponding of water in roads and
poorly drained areas is also possible.

Early next week, a mid to upper-level trough approaching from the
western Atlantic will increase instability over the Northeast
Caribbean. At the same time, surface winds are expected to shift
to a more southerly direction around Monday as a frontal boundary
approaches from the west, increasing moisture content over the
region. Based on these features, there is an elevated risk of
flooding rains across the northern half of Puerto Rico on Monday
afternoon into the evening, along with a limited risk of
thunderstorms. Conditions across the US Virgin Islands on Monday
will depend on the evolution of these features; therefore,
residents and visitors are encouraged to stay tuned for forecast
updates as adjustments may be needed closer to the event.

&&

.Long Term(Tuesday through next Friday)...
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...
(18Z TAFS)
Issued at 1259 PM AST Sat Jan 3 2026

VFR conds expected. However, SHRA/+SHRA will form along the
Cordillera Central and downwind from El Yunque and around the USVI
this afternoon, some impacting JBQ creating MVFR conds. SHRA will
dissipate by around 03/23z. Improving overnight into early Sunday
morning, but with occasional -SHRA/SHRA moving near IST/ISX/JSJ.
Sea breeze influence will continue and winds will be mainly from
the ESE at 10-15 kt with higher gusts, becoming calm-light/VRB
overnight (23-13z) each day.

&&

.MARINE...
Issued at 1259 PM AST Sat Jan 3 2026

A surface high pressure building across the central Atlantic into
the northeast Caribbean will maintain light to moderate east to
east-southeast winds through at least early next week. A frontal
boundary and associated polar trough are expected to approach the
regional waters late Monday into Tuesday, resulting in a shift to
light northerly to northeasterly winds and an increased potential
for showers and isolated thunderstorms early next week. A small
northerly swell will arrive later tonight into Sunday, followed by
another pulse of longer-period northeasterly swell by the middle
of next week, which may lead to deteriorating marine conditions,
particularly for small craft and across exposed Atlantic waters
and Caribbean Passages.

&&

.BEACH FORECAST...
Issued at 1259 PM 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. As a
result, the risk of rip currents will remain moderate along
northern and east-facing beaches of Puerto Rico, including
Culebra, as well as along the shores of the north of St. Thomas
and St. John in the US Virgin Islands. While a high risk of rip
currents is not expected at this time, life-threatening rip
currents remain possible along these exposed beaches. Elsewhere
across Puerto Rico and the US Virgin Islands, the risk of rip
currents will remain low through the weekend.

Conditions are forecast to deteriorate by Tuesday as a longer-
period northeasterly swell arrives. This swell will produce
hazardous coastal conditions, including life-threatening rip
currents along exposed beaches. Beachgoers are strongly encouraged
to stay informed of the latest beach forecast updates.

&&

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

$$

MORNING CREW...CAM/GRS
EVENING CREW...ICP/MMC

NWS SJU Office Area Forecast Discussion