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FXCA62 TJSJ 020857
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Fri Jan 2 2026

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

.KEY MESSAGES...
Issued at 438 AM AST Fri Jan 2 2026

* Unstable conditions will continue today, with afternoon showers
  and isolated thunderstorms increasing the risk of ponding on
  roads and localized urban and small- stream flooding, especially
  across interior and southwestern Puerto Rico.

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

* Across the U.S. Virgin Islands, frequent isolated to scattered
  showers are expected to continue in the morning hours, promoting
  puddles over the road and brief periods of heavy rainfall.

* Another wet and unstable pattern is expected by early next week,
  bringing slow- moving showers and isolated thunderstorms that
  will likely lead to localized flooding and lightning risk.

&&

.Short Term(Today through Sunday)...
Issued at 438 AM AST Fri Jan 2 2026

A variable weather pattern persisted overnight, with cloudiness
across most of the western half of the CWA and some passing showers
across the Mona Passage spreading across the western Atlantic
offshore waters. At around 1 AM, the radar Doppler showed some
passing showers briefly moving through the northwestern sections of
Puerto Rico, leaving minimal rainfall accumulations. As of 4 AM,
satellite imagery and Radar Doppler continue to show the shower
activity associated with the mid to upper level trough moving just
north of the forecast area. Overnight temperatures were near
seasonal levels, with some areas slightly warmer in northwestern
sections due to cloud cover.

For the rest of today, an unstable weather pattern will persist as
the mid to upper-level trough moves eastward into the forecast area.
As this mid- to upper-level weather feature crosses the islands, the
divergence side of the trough will enhance colder temperatures at
500 MB, fluctuating between -8 and -9 degrees, and significant
amounts of moisture, as suggested by the 700-500 MB RH values. At
the surface, winds will remain variable as the frontal boundary
sinks into the Caribbean, persisting from the east-southeast,
becoming more from the east-northeast in the afternoon due to the
surface perturbation. Given the expected conditions, some showers
and thunderstorms are forecasted for this afternoon. The intensity
and coverage of the showers will depend entirely on the amount of
available moisture during the day. According to the NWS ensemble
model, widespread shower activity is not anticipated, and only the
western interior sections of Puerto Rico will experience showers. On
late Friday into the weekend, mid to upper level conditions will
rapidly improve as the subsidence side of the trough moves over the
forecast area. This pattern will favor a warm trend in the 500 MB
temperatures and more stable conditions, mostly provided by a strong
ridge that establishes at the 700 MB. At the same time, conditions
at the surface also improve, as a building surface high pressure
builds over the Central Atlantic and results in a more east wind
flow on Saturday. Under this surface pattern, trapped moisture at
850 MB will move in and out of the region, inducing some quick
passing showers, but not widespread activity, and short-lived
showers. On Sunday, the same mid to upper conditions will stay;
however, veering winds in response to an induced surface trough just
northeast of the Atlantic, north of the Hispaniola. These surface
conditions will drag patches of moisture and also a peak in the 925
MB temperatures, enhancing warmer daytime temperatures on Sunday.

&&

.Long Term(Monday through Friday)...
Issued at 438 AM AST Fri Jan 2 2026

No major changes were introduced to the long-term forecast, with
a wet and unstable weather pattern early next week, gradually
improving by the mid week. As mentioned in the previous
discussion, the polar trough is still expected to deepen well
enough into the northeastern Caribbean, increasing moisture
content and introducing instability. Based on the latest model
guidance, PWAT values are likely to increase to above
climatological normal (up to 1.75 inches), with a high increase in
low to mid level moisture content. The presence of the trough
could bring cooler-than- normal 500 mb temperatures (between - 9
and -10 degrees Celsius) and strong upper-level winds (between 60
and 80 kt), which should enhance ventilation and allow cloud
growth, increasing thunderstorm potential. In addition to the
polar trough, another frontal boundary is expected to approach the
local area, creating a col region and weakening surface winds.
The most likely scenario for Monday into Tuesday is afternoon
convection, mainly concentrated over the mountain ranges of Puerto
Rico, with an advective cooling pattern during the night into the
morning affecting the northern portions of Puerto Rico and St.
Thomas and St. John in the U.S. Virgin Islands. With light and
variable surface winds, most of the showers and thunderstorms
should remain stationary, increasing flooding potential. Theres a
medium to high chance of rainfall accumulations leading to
flooding in urban areas, roads, and small streams. However, cloud
cover associated with the trough may be an inhibiting factor for
afternoon convection.

As the trough moves away, a surface high pressure exiting CONUS is
expected to build in the western Atlantic, increasing winds and
promoting a NE-ENE wind pattern. PWAT values should gradually drop
to below normal (between 0.9 - 1.1 inches) as a drier air mass
should filter into the region. Patches of moisture embedded in the
trades will arrive from time to time, bringing a few isolated
showers over windward sections, particularly at night into the
morning hours. Shallow afternoon convection is still likely each
day, particularly over western/southwestern Puerto Rico, although no
flood or lightning threat is expected during that period.

As winds are expected to become from the NE-ENE, temperatures will
gradually return to seasonal and even below climatological normal
based on the latest guidance. For urban and lower elevations,
minimum temperatures may remain in the low to mid 70s, with isolated
areas dropping into the high 60s. On the other hand, higher
elevations should remain in the 60s, with isolated areas dropping
into the mid to high 50s.

&&

.AVIATION...
(06Z TAFS)
Issued at 438 AM AST Fri Jan 2 2026

VFR conditions will prevail across all TAF sites during the period.
Increasing cloudiness will result in high ceilings generally between
FL030 and FL050. VCSH will affect the western TAF sites during the
morning hours, then spread to the remaining terminals. Surface winds
will remain variable, becoming ESE at up to 12 knots around 02/15Z,
then diminishing to light and variable again near 02/23Z. Around
02/19Z, brief reductions in ceilings and visibility are possible due
to SHRA over the mountainous areas.

&&

.MARINE...
Issued at 438 AM AST Fri Jan 2 2026

A surface high pressure over the central Atlantic, and a frontal
boundary north of the region will promote light to moderate trade
winds for the next few days. This front and associated upper-level
trough will continue to bring showers and isolated thunderstorms
across the Mona Passage and local Atlantic waters today, leading to
localized choppy seas. Another frontal boundary and polar trough are
expected to approach the local area by Monday, weakening winds and
becoming light from the northeast.

&&

.BEACH FORECAST...
Issued at 438 AM AST Fri Jan 2 2026

The moderate rip current risk is expected to continue across
western, northern, and eastern beaches of Puerto Rico, including
Culebra, and St. Thomas and St. John in the U.S. Virgin Islands this
weekend, becoming low on Monday. Beachgoers are encouraged to
exercise caution, as life-threatening rip currents are possible
along the surf zone. The latest model guidance suggests a long-
period northeasterly swell expected to arrive by late Tuesday night,
deteriorating beach and coastal conditions. At the moment, a high
risk of rip currents is likely, particularly over north and east-
facing beaches of Puerto Rico and the U.S. Virgin Islands, on
Wednesday. Beachgoers are urged to stay tuned for the next updates.

Besides rip currents, beachgoers are also encouraged to remain
weather alert, as isolated thunderstorms may develop this afternoon
and move over western portions of Puerto Rico, increasing the
lightning threat. Beachgoers are urged to seek shelter if they hear
thunder.

&&

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

$$

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

NWS SJU Office Area Forecast Discussion