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320
FXCA62 TJSJ 180806 CCA
AFDSJU

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
406 AM AST Tue Nov 18 2025

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

.KEY MESSAGES...
Issued at 348 AM AST Tue Nov 18 2025

* Life-threatening rip currents are expected along the north-
  facing beaches in Puerto Rico, Culebra, and the eastern half of
  St. Croix through Wednesday afternoon.

* Showers and isolated thunderstorms due a surface trough will
  increase the flooding and lightning risk today, particularly
  over western and northeastern Puerto Rico.

* Passing showers will bring periods of moderate to locally heavy
  rain across the US Virgin Islands throughout the day.

&&

.Short Term(Today through Thursday)...
Issued at 348 AM AST Tue Nov 18 2025

Afternoon convection linger into the early evening hours across
Arecibo, leaving rainfall accumulations of just over one inch.
Additionally, the frequency of showers increased along the east, with
nearly half an inch collected. Later in the overnight hours, showers
also moved across the Virgin Islands. The heaviest activity was
observed over eastern St. Croix, and also in St. John. Elsewhere,
skies were mostly clear. Temperatures dropped into the low 60s or
even a tad cooler in the mountains of Puerto Rico, with lows in the
low and mid 70s in the coastal areas of the U.S. Caribbean
territories.

A surface trough moving across the region today will bring
increasing moisture to the islands, with a moderate easterly breeze
at the surface and southeast winds higher up steering showers and
storms toward the west and west-northwest. Despite a weakening mid-
level ridge, temperatures aloft will continue to cool ahead of the
approaching mid- to upper-level trough, marking the onset of an
unstable period beginning this afternoon. This setup will make today
the wettest day of the period, with showers and isolated to locally
scattered thunderstorms clustering across the central and western
interior of Puerto Rico, with the strongest activity expected over
the western hills. Additional pockets of heavy rain may also develop
downwind of Sierra de Luquillo and the local islands, affecting
parts of the San Juan metro area. Heavy downpours could cause
localized flooding, with minor flooding or ponding of water possible
in low-lying or poorly drained areas. Temperatures will remain near
normal, with a few urban locations briefly reaching around 90F.
Hazard Summary for Today: Expect a low to locally moderate flooding
risk from heavy downpours and isolated to locally scattered
lightning strike risk with thunderstorms.

The mid-to upper-level trough will continue to move in tonight,
keeping conditions unstable as colder mid-level temperatures
persist. Once the trough axis moves through on Thursday morning,
warming aloft and very dry air will quickly stabilize the
atmosphere. At the surface, high pressure moving into the western
Atlantic will strengthen local winds and shift them to the northeast
tonight into Wednesday, producing a fresh breeze. On Thursday, a
weak surface trough east of the Leeward Islands will help maintain
the north-to-northeast flow, although at more moderate intensities.
This pattern will bring in some moisture early on but will also push
the existing moisture plume southward, allowing much drier and
slightly cooler air to settle in later in the period. Moisture will
be the main factor influencing rainfall, with levels rising slightly
above normal tonight, returning to typical values Wednesday morning,
and then steadily falling to well below normal by late Thursday.
Overall, showers and thunderstorms will be more limited on
Wednesday, with only a few brief storms possible, and by Thursday
the weather will become mostly stable with little to no thunder
expected. Despite the drying trend, a passing trade wind showers may
still occur overnight, even during the driest periods, due to the
steady northeast flow. Cooler temperatures near the surface will
continue and may bring the first hint of a friito navideno feel
later in the week. Hazard Summary for Tonight through Thursday: A
limited flooding and lightning risk from locally heavy downpours
produced by a few thunderstorms on tonight into Wednesday.

&&

.Long Term(Friday through Tuesday)...
Issued at 348 AM AST Tue Nov 18 2025

The long-term forecast remains on track, with mostly fair conditions
for the upcoming weekend, becoming variable early next week. A
surface high pressure is still expected to build over the Western
Atlantic by Friday, promoting northeasterly winds through most of
the period. As a drier air mass should filter into the region, the
latest deterministic guidance from the GFS and ECMWF continues to
suggest PWAT values mostly below climatological normal (1.2 - 1.4
inches), with a few members opting for more seasonal values (1.4 -
1.6 inches). A mid-level ridge should also establish, warming 500 mb
temperatures (around -5.5 degrees Celsius), and promoting stability
aloft and limiting deep convection activity. Additionally, the
Galvez-Davison Index (GDI) suggests a low potential of thunderstorm
development across the CWA. As mentioned in the previous discussion,
the most likely scenario would be passing showers over windward
sections in the late night and morning, with limited afternoon
convection over the mountain ranges and southwestern portions of
Puerto Rico. Although rainfall accumulations should not present a
flooding threat, expect ponding of water over roadways, urban, and
poorly drained areas. On Monday and Tuesday, PWAT values are
expected to increase to more seasonal levels due to patches of
moisture moving across the CWA, resulting in an increased frequency
of showers. Nevertheless, no significant flooding or lightning risk
is expected across the region.

Once again, cooler temperatures are likely across the CWA during the
forecast period, as the latest guidance keeps suggesting a fall in
925 mb temperatures, well below normal. Under a northeast wind flow,
the heat threat will remain low throughout the long-term period.

&&

.AVIATION...
(06Z TAFS)
Issued at 348 AM AST Tue Nov 18 2025

SHRA and iso TSRA are occurring near TJSJ and USVI terminals and
will continue at times thru the prd. Aftn convection will expand
toward TJBQ and TJPS, and all sites may experience brief MVFR due to
mtn obsc and reduced VIS. SHRA will decrease aft 18/22Z but may
linger near TJSJ and USVI terminals overnight. Winds will remain
LGT/CALM and VRB early, increase to 812 kt btwn 18/13Z18/22Z, then
return to LGT/VRB overnight.

&&

.MARINE...
Issued at 348 AM AST Tue Nov 18 2025

Winds from the east will increase and become moderate today,
shifting from the northeast by Wednesday night. The approach of a
surface trough will bring showers and isolated thunderstorms across
the local water and passages, likely to generate localized hazardous
marine conditions for small craft. Pulses of a north northeasterly
swell will continue to spread across the Atlantic waters and local
passages through Wednesday.

&&

.BEACH FORECAST...
Issued at 348 AM AST Tue Nov 18 2025

No changes were introduced to the beach forecast. Pulses of the
northerly-northeasterly swell will continue to spread across the
Atlantic waters and passages, promoting hazardous beach
conditions. Hence, the high risk of rip currents remains for the
northern and eastern beaches of Puerto Rico, including Culebra,
and St. Croix in the U.S. Virgin Islands through Wednesday
evening. Visitors and residents are encouraged to check the beach
forecast before going, heed the advice of the flag warning system,
and always swim near a lifeguard.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Wednesday afternoon for PRZ001-002-
     005-008-012.

VI...High Rip Current Risk through Wednesday afternoon for VIZ002.

AM...None.
&&

$$

SHORT TERM/AVIATION...ICP/ERG
LONG TERM/MARINE...MNG

NWS SJU Office Area Forecast Discussion