625
FXCA62 TJSJ 091703
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
Issued by National Weather Service Melbourne FL
103 PM AST Tue Dec 9 2025

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

.KEY MESSAGES...
Issued at 1249 PM AST Tue Dec 9 2025

* Marine and beach conditions will deteriorate beginning
Thursday. Expect choppy to rough seas and life-threatening rip
currents.

* Winds increase late in the week, leading to breezy to windy
conditions across coastal and elevated areas. Light-weight outdoor
items may be blown around in exposed locations.

* For Puerto Rico, showers are expected to continue during
the morning hours across the east/southeastern portions. Over
west/northwest PR, afternoon showers are expected each day. Peak
heat indices to around 100 deg F are expected near the coast.

* For the U.S. Virgin Islands, passing showers will continue
throughout the morning, becoming frequent later tonight and early
tomorrow.

&&

.Short Term (This evening through Thursday)...
Issued at 1249 PM AST Tue Dec 9 2025

SYNOPTIC OVERVIEW:
Puerto Rico and the USVI reside on the southwestern periphery of
a stout (592 dam) H5 ridge. Proximity soundings reveal a dry,
subsident regime in the mid to upper troposphere. In the lowest 10
KFT, light to moderate SE flow persists. Weak vorticity maxima
are embedded in the SE flow, accompanied by brief surges of low-
level moisture. This overall pattern is forecast to continue
through the period. H85 Ts are projected to remain near to
slightly above normal.

SENSIBLE WEATHER/IMPACTS:
At least two weak disturbances are forecast to pass over the
district over the next couple of days, the first of which is
marching its way westward across PR this afternoon. Showers are
already in progress, with an initial windward focus shifting
toward the interior and western half of PR. Satellite imagery
shows this progression well, with skies clearing out over the
USVI. Sufficient instability is in place, but cloud towers will
ingest very dry air above 10 KFT, leading to mostly low-topped
downpours void of lightning. Briefly drier conditions are expected
area-wide through the evening as we sit between disturbances.

After midnight, hi-res guidance suggests the next wave of energy
approaches USVI, leading to scattered shower redevelopment. This
feature appears to have slightly better moisture and instability,
so additional showers and a low chance for lightning continue into
Wednesday. Relatively speaking, the lightning potential is highest
(20%) as the overall coverage slowly shifts to western PR
tomorrow afternoon. A third, and even weaker, disturbance is
slated to pass overhead by Thursday, preserving the oscillation
between sunshine and scattered showers. Any excessive rainfall /
flooding threat appears limited to especially sensitive locales in
higher terrain: the experimental REFS shows only spotty chances
(10-20%) for in excess of 2" of rain through Thursday.

On Wednesday, expect a few gusts to around 25 mph on the east-facing
coasts, Vieques, and the USVI. Elsewhere, moderate SE breezes should
keep temperatures near to slightly warmer than normal, with peak
heat indices along the coast from 96-101 deg F each afternoon.

&&

.Long Term (Friday through next Monday)...
Issued at 1249 PM AST Tue Dec 9 2025

SYNOPTIC OVERVIEW:
The anomalous upper ridge over the Central Atlantic is
anticipated to retrograde slightly and expand across the NE
Caribbean late this week, deflecting a deep trough on the US East
Coast well north of the islands. H5 heights are projected to
remain above normal through the period. Surface high pressure also
noses westward, enhancing the pressure gradient from Friday
through the weekend.

South of the ridge axis, guidance suggests that additional
perturbations of energy and moisture should clip the district as
they translate westward across the Caribbean Sea. These features
appear to be of a lower amplitude than those passing by during
the next 48 HR, which makes sense considering the large-scale
subsidence. Ensemble members hint at an approaching front around
next Tue/Wed, but it is currently forecast to stall and dissipate
somewhere near the Turks & Caicos and/or Hispaniola.

On the whole, moisture profiles remain consistent throughout,
characterized by seasonable low-level RH and very dry parcels
above H7. Due to the ridge and invariably warmer-than-average
SSTs, PBL temperatures should continue to run on the warmer side
of seasonal averages.

SENSIBLE WEATHER/IMPACTS:
At best, scattered (30-50%) coverage of showers is forecast
through the period, with coverage highest over eastern PR to USVI
overnight/morning before shifting to the western half of PR in the
afternoon/evening. The exact timing of these showers will be
modulated by the passage of the weak disturbances. Still, we
expect quite a bit of dry time through at least the weekend. As
the ridge weakens and a weakening front draws closer early next
week, rain chances subtly increase (40-60%).

Breezy conditions are anticipated over the weekend. East winds
gusting to 20-25 mph are forecast, particularly at the coast. This
may give slight relief from the heat, but max heat indices still
approach 100 deg F over lower elevations.

&&

.AVIATION...
(18Z TAFS)
Issued at 1249 PM AST Tue Dec 9 2025

Weak disturbances will occasionally produce scattered showers,
with activity favoring the USVI and San Juan area terminals in the
morning hours before shifting toward the interior and west of PR
in the afternoon (JBQ). The chance of lightning activity is non-
zero but small, generally 20% or less. Prevailing VFR, except for
brief categorical restrictions within showers. Broad east to
southeast flow persists through the period, becoming somewhat
gusty at IST and ISX on Wed.

&&

.MARINE...
Issued at 1249 PM AST Tue Dec 9 2025

(modified previous discussion) A broad surface high pressure over
the Central Atlantic will promote east to southeast gentle to
moderate winds through Wednesday. The high then strengthens,
tightening the pressure gradient and increasing winds, allowing
seas to build across the Atlantic waters and exposed passages.
Additionally, a long-period northerly swell arriving early
Thursday will further worsen conditions. Choppy to rough seas are
expected, with Small Craft Advisories likely by the end of the
workweek. A gradual improvement remains possible by the weekend as
winds and swell ease.

&&

.BEACH FORECAST...
Issued at 1249 PM AST Tue Dec 9 2025

(previous discussion) A moderate risk of rip currents will
continue over the north and east-facing beaches of Puerto Rico and
the U.S. Virgin Islands through at least Wednesday. Beachgoers
are encouraged to exercise caution as life-threatening rip
currents are possible along the surf zone. A long-period northerly
swell is expected to arrive early on Thursday and spread across
the local waters and passages. Combined with increasing winds,
beach conditions are very likely to deteriorate and become
dangerous, mainly along north-facing beaches of the islands.
Residents and visitors are urged to check the beach forecast
before going out, and heed the advice of the flag warning system.
As the swell eases and winds weaken, beach conditions should
improve by the latter part of the weekend.

&&

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

$$

SHORT TERM...Heil/MLB
LONG TERM....Heil/MLB
AVIATION...Heil/MLB