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

325
FXCA62 TJSJ 221808
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
208 PM AST Mon Dec 22 2025

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

.KEY MESSAGES...
Issued at 132 PM AST Mon Dec 22 2025

* Marine and beach conditions will deteriorate by mid week and
  may extend for the weekend, becoming hazardous for small craft
  and beachgoers.

* Shower and thunderstorm activity will increase tomorrow,
  leading to ponding of water over roadways and poorly drained
  areas, gusty winds, and localized flooding over northern and
  eastern Puerto Rico.

* Below normal temperatures will likely enhance patchy fog across
  interior sections of Puerto Rico, reducing visibility and
  becoming hazardous for drivers by the end of the workweek.

&&

.Short Term(This evening through Wednesday)...
Issued at 132 PM AST Mon Dec 22 2025

Variable weather conditions persisted during the early morning hours
as a disturbance, and northeasterly wind flow resulted in a cool
advective pattern, with showery weather affecting windward coastal
areas of the islands. However, showers moved fairly quickly, leaving
less than half an inch of rainfall. GOES-19 PWAT imagery shows a
drier slot that will move over the region this afternoon and
evening. Therefore, the frequency of showers will diminish for the
rest of the day, although isolated to scattered showers are expected
to develop over southwestern Puerto Rico this afternoon with no
substantial impacts.

The remainder of the short-term forecast will continue to be
dominated by the presence of a polar trough at upper levels. All
ingredients necessary for instability aloft will be in place, as 250
mb height fields and 1000-500 mb thicknesses are expected to drop
well below normal. Cold air advection will promote 500 mb
temperatures cooling to between -9 and -10 degrees Celsius, which
is at or below the 10th percentile of climatological normals.
This setup will promote steep 700-500 mb lapse rates.
Additionally, favorable jet dynamics will move over the forecast
area, with a 65-80 kt jet at 250 mb promoting enhanced ventilation
aloft with increased 0-500 mb bulk shear, a pattern often
associated with organized convection.

However, the limiting factor will be available moisture across the
northeastern Caribbean. The associated frontal boundary is currently
northwest of the area and will gradually sink southward. Unlike
previous model cycles that indicated abundant columnar moisture,
recent runs now show fragmented pockets of moisture moving across
the region from time to time, with PWAT values remaining near normal
to below normal through Wednesday. Additionally, the northeasterly
steering wind flow will keep temperatures below normal, which
could reduce afternoon surface heating needed to fuel deep
convection. As a result, any convection that develops is expected
to be localized rather than widespread. Relatively fast steering
winds will also limit rainfall accumulations, even in areas
experiencing heavier showers.

Therefore, expect showery weather during the night and morning
hours, with isolated thunderstorms developing mainly over the
regional waters. Some of these thunderstorms could move close to
coastal areas, particularly over the Atlantic waters. During the
afternoon, showers and a few thunderstorms may develop over interior
and southwestern Puerto Rico. Overall, a limited flooding threat is
expected, mainly consisting of ponding of water on roads and in
poorly drained areas.

&&

.Long Term(Thursday through next Sunday)...
Issued at 530 AM AST Mon Dec 22 2025

Current model guidance suggest precipitable water (PWAT) values
of around 1.4 inches to start the period. A series of mid to upper
level troughs will move north of the region through the Friday,
while a cold front approaches and likely moves over the region on
Thursday (Christmas Day). Although they start an upward trend,
instability is evident as 500 mb temperatures will still be below
normal on Thursday at -10 to -8 degrees Celsius. A limited
flooding risk will be present for most of the region, as the
frontal boundary moves over the region, resulting in showers and
possible isolated t-storms under north-northeast steering flow.
Model guidance has been fairly consistent with each run regarding
the approach of these features. With uncertainty remaining in the
exact impacts across Puerto Rico and the U.S. Virgin Islands. As
drier air behind the front will promote improved weather
conditions with a cooling trend continuing Friday through Monday,
925 mb temperatures are forecast to be below normal for this
period. Lows 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. Highs
are forecast in the around the mid 80s across lower elevations of
the islands, with isolated/urban areas a bit higher. Although
PWAT values are forecast at around to below an inch, isolated
patches of moisture will reach the area and promote passing
showers from time to time.

&&

.AVIATION...
(18Z TAFS)
Issued at 132 PM AST Mon Dec 22 2025

VFR conds prevail at most TAF sites thru the fcst pd. SHRA/VCSH will
continue to affect mainly TJSJ, TIST and TISX at times, with brief
MVFR cigs/vsbys psbl, especially ovrngt and early mrng. Aft 23/14Z,
SHRA may develop ovr interior and SW PR, with limited impacts
expected. Winds ENE 6-15 kt, becoming locally gusty near SHRA.

&&

.MARINE...
Issued at 132 PM AST Mon Dec 22 2025

A building 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 fading northeasterly swell
will promote seas up to 6 feet for the offshore Atlantic Waters for
the rest of today; small craft should continue to exercise caution.

A series of surface highs and frontal lows will continue moving into
the Atlantic during the period, resulting in moderate to locally
fresh east to northeast winds through at least Wednesday, becoming
moderate once again by Friday.  Marine conditions will briefly
improve tonight into early Tuesday; nevertheless, a long-period
northerly swell, from one of the above mentioned frontal lows, will
arrive and spread across the Atlantic waters and passages. This will
result in choppy to rough seas over the offshore Atlantic Waters by
Tuesday afternoon, becoming hazardous for small craft. These
conditions will continue through the workweek as seas build to 6 to
9 feet and spread to the nearshore Atlantic Waters and local
Passages.

&&

.BEACH FORECAST...
Issued at 132 PM AST Mon Dec 22 2025

Beach conditions remain suitable for beachgoers, with moderate
rip currents on the northern and eastern beaches of Puerto Rico,
including Vieques and Culebra, as well as the U.S. Virgin Islands.
Nevertheless, beachgoers are encouraged to exercise caution as
life- threatening rip currents are possible along the surf zone.
Although the risk will remain moderate, a long-period northerly-
northeasterly is expected to arrive by Wednesday and spread across
the local waters and passages, deteriorating beach and marine
conditions. Hence, the risk of rip currents will likely be high on
Wednesday, particularly along the north and east-facing beaches
of Puerto Rico, Culebra, and the U.S. Virgin Islands. The risk is
expected to remain high as pulses of another long-period northerly
swell will deteriorate once again the beach conditions by the
weekend. Due to previous swell activity across the islands, and
large breaking waves expected, High Surf Advisories cannot be
ruled out. Residents and visitors are encouraged to review the
beach forecast at https://www.weather.gov/beach/forecast?site=sju&action=
and stay tuned for the next updates.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory from noon Tuesday to midnight AST Thursday
     night for AMZ711.

&&

$$

SHORT TERM/AVIATION...CVB
LONG TERM....MRR
MARINE/BEACH FORECAST...CVB/MNG

NWS SJU Office Area Forecast Discussion