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002
FXCA62 TJSJ 230937
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
537 AM AST Tue Dec 23 2025

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

.KEY MESSAGES...
Issued at 537 AM AST Tue Dec 23 2025

* The short-term weather pattern remains largely unchanged, with
  unstable conditions expected from December 24 through December
  25 for the region.

* A limited flooding threat is expected through Thursday, mainly
  ponding of water over roadways and poorly drained areas for PR
  and the USVI.

* Marine and beach conditions will gradually deteriorate today and
  tomorrow; these conditions will continue throughout the week as
  pulses of northerly swell arrive. Small Craft Advisories and
  High Risk of Rip Currents will soon be in effect.

&&

.Short Term(Today through Thursday)...
Issued at 537 AM AST Tue Dec 23 2025

Overnight conditions were relatively calm, with pockets of passing
showers over the regional waters, some of which reached northern and
eastern sections of eastern Puerto Rico. Temperatures remained cool,
with readings in the 60s across the higher elevations and in the 70s
across urban and coastal areas. The prevailing wind flow was from
the northeast at 5 to 10 mph, with occasional higher gusts near
passing showers.

The overall short-term weather pattern has not changed
significantly, therefore much of the previous discussion remains
valid. From December 24 through December 25, atmospheric conditions
will remain unstable due to the continued influence of a polar
trough at upper levels. Mid-level temperatures between 700 and 500
mb are expected to remain around 10 degrees Celsius, which is at or
below the 10th percentile for this time of the year. This
anomalously cold air aloft will support steep lapse rates and
increased instability. In addition, favorable jet dynamics will
overspread the forecast area, with a 6090 kt jet at 250 mb
enhancing upper-level ventilation and increasing 0500 mb bulk
shear, a pattern often associated with more organized convection.
Nevertheless, the primary limiting factor will continue to be
available moisture across the northeastern Caribbean. The associated
frontal boundary remains northwest of the area and is forecast to
gradually sag southward. Precipitable water values are expected to
remain near normal to slightly below normal through Thursday.
Additionally, the persistent northeasterly low-level flow will keep
temperatures below normal, potentially limiting afternoon surface
heating and further restricting deep convective development.

As a result, any convection that develops is expected to be
localized rather than widespread. Relatively fast steering winds
will continue to limit rainfall accumulations, even where heavier
showers occur. Overall, expect periods of showers during the
overnight and morning hours, with isolated thunderstorms developing
mainly over the regional waters. Some thunderstorms may approach
coastal areas, particularly across the Atlantic waters. During the
afternoon hours, showers with isolated thunderstorms may develop
over interior and southwestern Puerto Rico.

At this time, there is a limited flooding threat through Thursday,
December 25, primarily in the form of ponding of water on roads and
in poorly drained areas.

&&

.Long Term(Friday through Tuesday)...
Issued at 537 AM AST Tue Dec 23 2025

Drier air behind the frontal boundary will dominate throughout the
the period. Precipitable Water (PWAT) values are forecast at
around to below an inch with isolated patches of moisture (PWAT up
to around 1.2 in) reaching the area and promote passing showers
from time to time. Although low PWAT values are forecast, upper
troughs will move northeast of the area during the latter part of
this week. building surface high over the western Atlantic and a
frontal low over the north-central Atlantic will promote
northeasterly steering flow to start the period. Model guidance
suggests that winds will gradually veer to start the next week,
promoting southeasterly flow by the end of the period. Under the
northeasterly flow, 925 mb temperatures are forecast to be below
normal. Minimum temperatures are forecast in the 50s to low 60s
across higher elevations of PR, in the upper 60s to mid 70s across
lower elevations of PR, and in the low to mid 70s across the
USVI. Maximum temperatures are forecast around the mid 80s across
lower elevations of the islands, with isolated/urban areas a bit
higher. This will likely enhance patchy fog across sectors of
interior Puerto Rico.

&&

.AVIATION...
(06Z TAFS)
Issued at 537 AM AST Tue Dec 23 2025

All TAF sites should experience VFR conditions  across most
terminals through the period. However, SHRA may intermittently
affect TJSJ, TIST, and TISX, especially during the overnight and
early morning hours. TJPS could experience VCSH after 1217Z. Winds
will remain from the NE at 6-10 knots, with occasional higher gusts
near passing showers.
&&

.MARINE...
Issued at 537 AM AST Tue Dec 23 2025

A surface high over the western Atlantic and a frontal low over the
north-central Atlantic will promote moderate east to northeast winds
to start the period. A series of surface highs and frontal lows will
continue moving into the Atlantic during the period, resulting in
moderate to locally fresh northeast winds through at least Wednesday,
becoming moderate by Thursday.

A long-period northerly swell, from the above mentioned frontal
low, will arrive and spread across the offshore Atlantic waters
this afternoon. This will result in choppy to rough seas, becoming
hazardous for small craft. These conditions will continue
throughout the week as seas build to 6 to 9 feet, spreading to the
nearshore Atlantic Waters and local Passages. Another pulse of
swell will arrive later in the workweek and support deteriorated
conditions throughout the end of the week.

&&

.BEACH FORECAST...
Issued at 537 AM AST Tue Dec 23 2025

Although the day will start with a moderate risk of rip currents
for the northern and eastern coastline of Puerto Rico, as well as
for exposed beaches of Culebra and the USVI, conditions will
deteriorate late tonight as a northerly swell arrives. This
northerly long-period swell will increase the risk of rip currents up
to high for exposed northern beaches by late tonight and
throughout the rest of the week. Another pulse of swell will
arrive later in the workweek and support deteriorated conditions
throughout the end of the week. Please continue to monitor the
forecast for updates as conditions evolve.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from this evening through late Thursday
     night for PRZ001-002-005-008.

VI...None.
AM...Small Craft Advisory from noon today to midnight AST Thursday
     night for AMZ711.

     Small Craft Advisory from noon Wednesday to midnight AST
     Thursday night for AMZ712.

&&

$$

SHORT TERM/AVIATION...MMC
LONG TERM/MARINE/BEACH FORECAST...MRR

NWS SJU Office Area Forecast Discussion