372
FXCA62 TJSJ 171857
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
257 PM AST Mon Nov 17 2025

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

.KEY MESSAGES...
Issued at 219 PM AST Mon Nov 17 2025

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

* We have a moderate/high risk (40-60%) chance of observing
  showers and thunderstorms across the interior/west of PR this
  afternoon.

* A surface trough will increase the frequency of passing
  showers, producing periods of moderate to locally heavy rain
  across the US Virgin Islands and eastern PR overnight into
  tomorrow.

&&

.Short Term(This evening through Wednesday)...
Issued at 219 PM AST Mon Nov 17 2025

The skies across the US Virgin Islands and Puerto Rico remained
mainly sunny throughout the morning, with some clouds developing
across the interior of PR, downwind from La Sierra de Luquillo,
and over the interior of St. Croix around noon. The Doppler Radar
observed near El Yunque and isolated areas in the interior of PR.
The winds had an east-southeast component, with speeds ranging
from 5 to 15 mph, and exhibited sea breeze variations. Some
showers developed downwind from St Croix. Maximum temperatures
ranged from the mid-80s to the upper 80s along the coastal
locations, and from the mid- to upper 70s along the mountains.

The surface high pressure across the Central Atlantic will
continue to promote an east-to-east-southeast wind flow today,
resulting in afternoon convection along and northwest of the
Cordillera Central. TJSJ 12z RAOB observed moisture values near or
below climatology, with 1.30 inches of Precipitable Water (PW).
Another observation is that we noted some warming at 500 mb,
accompanied by modest instability at low and mid-levels.
Furthermore, we are experiencing some dry air intrusion, which
will limit afternoon and evening convection unless local sea
breeze convergence and diurnal heating enhance rainfall.
Therefore, we expect isolated to scattered showers and
thunderstorms, enhanced by local topography and sea breeze
fluctuations, over the interior and west PR, downwind from El
Yunque and the US Virgin Islands.

A surface trough will promote moisture increment overnight, with
more frequent passing showers across the USVI and PR`s windward
locations. This activity will increase the chance of observing
periods of moderate to locally heavy rainfall. Although dry air
aloft will persist tomorrow, moisture levels will rise all the way
up to 600 MB, promoting a better chance for thunderstorms to
develop during the afternoon. Thus, the risk of observing flooding
rains tomorrow will range from limited to relatively elevated,
mainly over Puerto Rico. Most of the activity near the USVI will
remain over the surrounding waters, but there is a slight chance
that this activity moves occasionally inland.

By Wednesday, there will be a greater chance of favorable
conditions for convection as a deepening polar trough moves east
across the western Atlantic into the northeastern Caribbean. In
the afternoon and evening, the region will likely experience
increased instability, with 500 mb temperatures dropping to -8 to
-9 C and steepening lapse rates between 700 and 500 mb. This
suggests a higher likelihood of widespread showers and isolated
thunderstorms.

Although northeasterly winds may limit heating in some areas,
stronger upper-level forcing is expected to support convective
development, resulting in showers and thunderstorms that may
linger overnight over Atlantic waters and occasionally move
inland. Consequently, the flood risk will increase, particularly
in areas with repeated showers.

Regarding local temperatures, they will continue to be slightly
above normal, but heat impacts remain unlikely, and a cooling
trend is likely on the horizon.

&&

.Long Term(Thursday through next Sunday)...
Issued at 219 PM AST Mon Nov 17 2025

A gradual improvement in the weather conditions is still anticipated
by the end of the workweek into the upcoming weekend. Thursday
may be the wettest day of the period due to lingering moisture
across the region and the influence of the polar trough. From the
deterministic guidance of the GFS and ECMWF, seasonal Precipitable
Water values (1.5 - 1.6 inches) and colder 500 mb temperatures
(around -8.5 degrees Celsius) are likely. Combined with local
effects and daytime heating , afternoon convection may develop
over the mountain ranges and southwestern Puerto Rico. Although
rainfall accumulations may not reach significant flooding
criteria, ponding of water over roadways, urban areas, and poorly
drained areas may lead to isolated urban and small stream flooding
over the aforementioned areas. By Friday, a surface high pressure
system should build over the western Atlantic, promoting mostly
NE winds. Weather conditions should improve over the weekend as
drier air filters into the region with a mid level ridge
dominating the weather pattern. From the latest model guidance,
PWAT values are likely to decrease and remain below climatological
normal (between 1.2 - 1.4 inches), while 500 mb temperatures will
get warmer than normal by the end of the period. Patches of
moisture will move occasionally across the CWA, bringing light to
moderate passing showers over windward sections of the islands in
the late night into the morning hours. Although afternoon
convection is expected, shower activity will likely be limited
under this weather pattern. Therefore, the flooding and lightning
threat is not expected for the rest of the forecast period.

Model guidance continues to suggest a fall in 925 mb temperatures,
being Thursday cooler than normal. Although the latest GFS
solution is tending to warmer temperatures for Saturday,
temperatures should remain seasonal, presenting no heat threat.
Hence, the heat risk should remain low for the rest of the period.

&&

.AVIATION...
(18Z TAFS)
Issued at 219 PM AST Mon Nov 17 2025

VFR conds are present across all TAF sites. The is still a slight to
moderate chance to observe a few short-lived thunderstorms over the
interior and W PR may bring VCSH/VCTS to TJSJ and TJBQ, with brief
MVFR and mtn obscurations possible. During the overnight period and
Tuesday morning, an increase in VCSH is forecast across USVI TAF
sites and TJSJ. E-SE below 10 kts, becoming calm overnight.

&&

.MARINE...
Issued at 219 PM AST Mon Nov 17 2025

A surface high pressure system will begin to dominate across the
central Atlantic, promoting moderate easterly winds from tonight
onward. Pulses of a north northeasterly swell will spread across
the Atlantic waters and local passages through Wednesday. Another
frontal boundary will approach north of the region around midweek,
promoting moderate winds to shift more from the northeast at the
end of the forecast period. Daily showers and isolated
thunderstorms could generate locally hazardous conditions for
small craft.

&&

.BEACH FORECAST...
Issued at 219 PM AST Mon Nov 17 2025

.BEACH FORECAST...

Pulses of north-northeasterly swells continue to spread across the
local waters. The San Juan buoy current observations show wave
heights around 4 feet at a period ranging between 10 to 14 seconds.
Based on calculations, that is resulting in breaking waves around 6
to 7 feet. As a result, the high risk of rip currents remains in
effect for the northern and eastern beaches of Puerto Rico, Culebra,
and St. Croix in the U.S. Virgin Islands this evening and will
continue through at least Wednesday afternoon. Residents and
visitors are urged to exercise caution, as life-threatening rip
currents are present along the surf zones. Heed the advice of the
flag warning system and swim near a lifeguard. Also, afternoon
convection may produce gusty winds and lightning, beachgoers should
remain weather alert and seek shelter whenever they hear thunder.
For more information specific to your location, visit
weather.gov/beach/sju.

&&

.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...CAM
LONG TERM....YZR
AVIATION...MMC