863
FXCA62 TJSJ 010940
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
540 AM AST Mon Dec 1 2025

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

.KEY MESSAGES...
Issued at 512 AM AST Mon Dec 1 2025

* This afternoon, the most active weather expected in southwest
  Puerto Rico this afternoon.

* Trade wind showers each night and morning across eastern and
  northern PR and the USVI. Showers and isolated thunderstorms
  each afternoon, increasing the flooding risk to limited from
  Tuesday through Thursday.

* The chance of thunderstorms will increase today through mid-
  week, with the highest potential Tuesday, especially for eastern
  PR and the USVI as a surface trough moves in from the east.

* A moderate risk of life-threatening rip currents are expected
  through the work week across the north exposed beaches of
  Puerto Rico and USVI.

&&

.Short Term(Today through Wednesday)...
Issued at 537 AM AST Mon Dec 1 2025

East-northeast trade winds brought passing showers across exposed
coastal areas of the U.S. Virgin Islands and northern and eastern
Puerto Rico, with a few reaching inland and leaving around half
an inch of rain in isolated spots of northeastern Puerto Rico.
Winds were influenced by the land breeze but still tended to come
from the east-northeast at 5 to 10 mph, while many inland
locations remained light or calm. Overnight temperatures dropped
into the low 60s in the higher elevations, with upper 70s across
the lower elevations.

Today, strong winds aloft will provide just enough lift to help
clouds grow and allow a few heavier showers to form. A shortwave
trough moving in from the west will add a little more support later
in the day. At the surface, winds will continue to weaken and turn
from ENE to NE as a surface trough approaches from the east.
Moisture will stay close to normal but will remain uneven across the
area. Passing trade-wind showers will continue this morning across
northern and eastern Puerto Rico and the U.S. Virgin Islands, but
they will become less frequent through the day. As the day
progresses, showers will form over land, mainly downwind from the
mountains and where the sea breeze is strongest. This includes areas
west-southwest of the islands and the Sierra de Luquillo, with the
most active weather expected in southwest Puerto Rico. One or two
isolated thunderstorms may form, but overall activity will stay
limited. Hazard summary for today: a limited lightning risk and a
low to no flooding risk, even if a thunderstorm develops.

Tonight, winds will continue to weaken as a surface trough moves in
from the east and the shortwave trough aloft gets closer. This will
make the environment slightly more favorable for thunderstorms,
though most activity should stay offshore. A few trade-wind showers
may still reach northern and eastern Puerto Rico and the U.S. Virgin
Islands, but they will be less frequent due to the lighter winds. On
Tuesday, the shortwave trough will move over the area, bringing the
coolest air aloft along with added instability and very weak
steering flow from the surface trough. These conditions make Tuesday
the most favorable day for thunderstorms, even if they remain
limited in coverage. Slow-moving showers or storms could bring heavy
rain, causing ponding of water or minor urban flooding. Tuesday
night, a few storms may linger or develop offshore under the
influence of the trough. By Wednesday, the trough will move away and
a mid-level ridge will build in, bringing warmer and drier air aloft
and a more stable pattern. Thunderstorm chances will drop sharply,
leaving only a small chance of one or two isolated afternoon showers
or storms. Hazard summary: limited lightning risk increasing tonight
and peaking Tuesday, with a limited flood risk also increasing
Tuesday; both risks lower on Wednesday.

&&

.Long Term(Thursday through Monday)...
Issued at 537 AM AST Mon Dec 1 2025

The long-term forecast remains without significant changes. An
upper-level trough will continue to influence the region by
Thursday, while an easterly disturbance approaches the islands,
sustaining a humid and somewhat unsettled pattern. Latest
precipitable water (PWAT) guidance shows moisture peaking Thursday
between 1.65 and 1.85 inches, which is above the climatological
norm for early December. This enhanced moisture will support
showers driven by a northeasterly flow, periodically affecting
windward areas. Afternoon convection is also possible, particularly
across interior and western Puerto Rico, where brief heavy downpours
and isolated thunderstorms cannot be ruled out, but the 500 mb
temperatures should warm to above-normal values and that might
slightly decrease the chance.

As a result, this period (Thursday) feature the highest precipitation
chance, posing a limited flood risk at this time, as rain
activity will likely result in ponding of water in roads and
poorly drained areas, and a low chance to observe urban and small
streams flooding. Winds are also expected to become breezier from
Thursday through the weekend. By Friday and into the weekend, a
high-pressure system over the western Atlantic will move north of
the islands. As ridging builds at various levels of the atmosphere,
more stable conditions are expected, with drier air arriving and
PWAT values falling below 1.4 inches, accompanied by moderate to
locally breezy easterly to northeasterly winds. Even so, lingering
moisture (20 to 50 percent chance of showers) will continue to
support occasional showers, especially during the overnight and
early morning hours.

Temperatures at 925 mb are forecast to be near-average values,
supporting seasonal surface temperatures. No heat-related risks
are anticipated at this time.

&&

.AVIATION...
(06Z TAFS)
Issued at 530 AM AST Mon Dec 1 2025

SHRA will affect TJSJ/TJBQ/TIST/TISX at times with brief MVFR
CIG/VIS, MNT OBSC, and short-lived VIS reductions thru the period.
TJPS may see brief MVFR with aftn SHRA/iso TSRA mainly 1/1622Z.
Winds thru FL015: E 1020 kt. SFC winds: LGT/VRB early, increasing
to 1216 kt with higher GUSTS and SBRZ inflow aft 1/13Z, then
becoming LGT/VRB again aft 1/22Z.

&&

.MARINE...
Issued at 530 AM AST Mon Dec 1 2025

A surface trough east of the islands will promote moderate
northeasterly winds today, allowing seas to subside slightly but
still supporting the small craft should exercise caution headline,
particularly across the offshore Atlantic waters. As this feature
approaches and moves across the CWA around Tuesday, winds will
become gentle to moderate from the east to southeast, then shift
to moderate from the east to northeast late Wednesday night.
Isolated thunderstorms will be possible across the waters over the
next few days.

&&

.BEACH FORECAST...
Issued at 530 AM AST Mon Dec 1 2025

Along the north and east facing beaches of Puerto Rico, including
Vieques and Culebra, and the U.S. Virgin Islands, there is a
moderate risk of rip currents today. These conditions are expected
to remain similar through the workweek, with some improvement as
winds diminish, particularly on Tuesday and Wednesday. Beachgoers
are urged to use caution, as a moderate risk means life-
threatening rip currents are possible in the surf zone. A low risk
persists elsewhere; however, even with a low risk, dangerous rip
currents can still develop near groins, jetties, reefs, and piers.
Visitors and residents are encouraged to always swim near a
lifeguard. For location-specific details, visit
weather.gov/beach/sju.

In addition to rip currents, beachgoers should remain weather
aware, as showers and isolated thunderstorms may move across
coastal areas of the islands.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory until 6 AM AST early this morning for
     AMZ711.

&&

$$

SHORT TERM/AVIATION...ICP
LONG TERM/MARINE/BEACH...YZR

NWS SJU Office Area Forecast Discussion