016
FXCA62 TJSJ 011731
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
131 PM AST Mon Dec 1 2025

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

.KEY MESSAGES...
Issued at 110 PM AST Mon Dec 1 2025

* A higher chance of thunderstorms on Tuesday for eastern Puerto
  Rico, with localized ponding of water and reduced visibility
  during heavier showers as a trough crosses the islands.

* Daily passing showers and a few afternoon thunderstorms will
  continue through the period in a seasonal pattern.

* For the U.S. Virgin Islands: passing trade-wind showers remain
  common, with a slight uptick in thunderstorm chances on Tuesday;
  brief heavy rain may create minor flooding.

* Moderate rip currents will persist through most of the week along
  the north and east coasts of Puerto Rico and the USVI. Small craft
  should exercise caution from Wednesday onward as a weak
  northeasterly swell and increasing winds return.

&&

.Short Term(This evening through Wednesday)...
Issued at 110 PM AST Mon Dec 1 2025

Mostly fair conditions prevailed across the islands during the
morning hours, with a few pockets of showers moving across the local
waters and passages, and some over the windward sections of the CWA.
Winds continued to weaken, with stations across the islands
reporting maximum gusts not exceeding 25 mph. Additionally, heat
indexes didnt exceed 100 degrees Fahrenheit, posing no threat
across the region. As forecasted, with winds from the ENE-NE,
afternoon convection started over the mountain ranges of Puerto Rico
and spread into the south-southwestern portions, with accumulations
below flooding criteria. Streamers from the islands also developed,
leaving low accumulations over eastern Puerto Rico.

No major changes were introduced to the short-term forecast. The
latest satellite-derived products show seasonal PWAT values over the
CWA (1.4 - 1.5 inches) and an induced surface trough just east of
the region with 1.6 - 1.8 inches. According to the latest model
solutions, the trough is expected to approach the local area later
tonight, weakening NE-E surface winds and pooling high moisture
content. Due to the presence of the trough, cooler-than-normal 500
mb temperatures, and ventilation aloft due to strong winds,
triggering upper-level dynamics will allow cloud growth, enhancing
deep convection activity. An advective pattern is expected to start
tonight, impacting mainly windward sections of the CWA throughout
the morning and afternoon convection over the mountain ranges and
southern Puerto Rico. Due to weakening winds, showers and isolated
thunderstorms may remain stationary, increasing flooding potential.
Although model guidance suggest rainfall accumulations that could
induce flooding in the afternoon, theres uncertainty introduced to
the forecast due to the possibility of high cloud coverage that may
inhibit convection. A similar weather pattern can be expected on
Wednesday, with limited flooding and lightning risk.

From the latest model guidance, 925mb temperatures may slightly
increase, reaching above climatological normal, with Wednesday being
the warmest day of the period. Although heat indexes in localized
area may reach 100 degrees Fahrenheit, these are not expected to
reach Heat Advisory Criteria. Hence, no heat threat is expected
during the forecast period.

&&

.Long Term(Thursday through next Sunday)...
Issued at 540 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...
(18Z TAFS)
Issued at 110 PM AST Mon Dec 1 2025

Mostly VFR conds across TAF terminals, with likely MVFR conds
over JSJ and IST late tonight. Aftn convection will likely bring
VCTS and -RA over JPS by 0118z, while the rest of sites may have
VCSH. PROB30 for JSJ and IST btwn 02/03-09z due sfc trough
approaching the CWA, reducing CIGs/VIS and promoting brf MVFR
conds. Winds will become light and VRB by 0123z, increasing btw 7
to 10kt by 02/13-14z.

&&

.MARINE...
Issued at 110 PM AST Mon Dec 1 2025

Moderate northeasterly winds will continue through Tuesday as a
surface trough approaches and crosses the region tomorrow. Seas will
gradually subside but will still warrant caution for small craft,
particularly across the offshore Atlantic waters. Isolated
thunderstorms remain possible over the local waters and may produce
brief gusty winds and locally higher seas.

After the trough moves through on Tuesday, winds will shift back to
a more easterly direction on Wednesday. A weak northeasterly swell
and increasing winds by midweek will maintain a moderate marine
hazard risk, mainly across the Atlantic waters.

Overall, seas are expected to remain moderate, but brief increases
in winds and wave heights may occur during passing showers or
isolated thunderstorms and again as winds strengthen midweek.

&&

.BEACH FORECAST...
Issued at 110 PM AST Mon Dec 1 2025

A moderate risk of rip currents will continue along the north and
eastfacing beaches of Puerto Rico, including Vieques and Culebra,
and across the U.S. Virgin Islands. These conditions are expected to
persist most of the week, as a weak northeasterly swell and
increasing winds arrive by Wednesday. A moderate risk means that
dangerous rip currents are possible and can quickly pull swimmers
away from shore.

Even where the risk is lower, rip currents can still form near
groins, jetties, reefs, and piers. Visitors and residents are
strongly encouraged to swim near a lifeguard and remain aware of
changing conditions.

Passing showers and an isolated thunderstorm may move across coastal
areas at times. Brief heavy rain could reduce visibility and may
cause hazardous conditions for beachgoers and small vessels near the
shore.

For the latest localized risk levels, visit weather.gov/beach/sju.

&&

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

$$

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