154
FXCA62 TJSJ 111808
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
208 PM AST Sat Oct 11 2025

.KEY MESSAGES...

*  External bands from Tropical Storm Jerry will continue to
   produce a variable weather pattern across the region at least
   until Sunday morning.

 * The U.S. Virgin Islands will experience periods of moderate to
   heavy showers through the rest of the afternoon and into
   Sunday morning.

 * A typical weather pattern will return on Sunday, featuring
   heat risks and afternoon convection. By Thursday, conditions
   will slightly change as a frontal boundary approaches the
   islands.

 * Marine conditions will continue to improve across the offshore Atlantic
   waters, with seas up to 6 feet and a moderate risk of rip
   currents.

&&

.SHORT TERM...Rest of Today through Monday...

During the morning hours a feeder band of Tropical Storm Jerry
remained nearly stationary just east and southeast of Puerto Rico,
near Vieques, Culebra, and the northern U.S. Virgin Islands. A
persistent land breeze off eastern and southern Puerto Rico limited
the bands inland progression. However, a Flood Advisory was issued
early for Vieques, while intense convection over St. Thomas prompted
a Flash Flood Warning. Radar estimates and local stations indicate
roughly 25 inches of rainfall across portions of the islands during
the morning. By midday, the area of convection over the offshore
Caribbean began to strengthen and shift northwestward toward
southern Puerto Rico, notably Santa Isabel and Salinas, aided by the
onset of the sea breeze.

This afternoon into this evening, Jerrys outer band and the
resultant southerly low-level flow will continue to advect very
moist air across the region. Hi-res model guidance favors additional
rounds of showers and thunderstorms developing over offshore
Caribbean waters and being advected onto the southern and
southeastern coastal municipalities of Puerto Rico. Convective
coverage may develop over the interior and be advected northward;
however, extensive cloudiness associated with Jerry could limit
diurnal heating and thereby suppress some of that activity. These
thunderstorms will be capable of frequent lightning, heavy rainfall,
and gusty winds. Locally heavy downpours could produce urban and
small-stream flooding, rapid rises on creeks and rivers, and
localized landslides in steep terrain.

Late tonight, convection should gradually diminish as diurnal
heating wanes, but isolated pockets of moderate to heavy rain will
persist offshore and may reach southeastern coastal municipalities
overnight. Flooding concerns will remain focused on low-lying urban
areas and basins that experienced rain earlier in the day.

As Jerry shifts farther north and away, the steering flow will
gradually veer more east-southeast. On Sunday, precipitable water
values are expected to remain well above normal and, combined with
strong daytime heating and local effects, will favor renewed
afternoon and early-evening convection, particularly over the
interior and northwestern portions of Puerto Rico. Thunderstorms
will again be capable of heavy downpours, frequent lightning, and
gusty winds.

By Monday, a drier air mass is forecast to filter into the region,
producing the driest and most stable conditions of the short-term
period. Model guidance shows PWATs falling to near 1.4 inches
(roughly two standard deviations below normal), which should
markedly reduce convective coverage and intensity. Isolated to
scattered afternoon showers or a stray thunderstorm cannot be ruled
out, but overall thunderstorm activity should be much reduced
compared to Sunday.

In terms of heat, east to east-southeast low-level winds will
continue to advect warmer-than-normal air through Sunday and into
Monday. Sunday will pose the greater heat threat as higher
temperatures combined with abundant low-level moisture could push
localized heat-index values to around or above 105F across urban and
coastal areas. Drier air moving in Monday should moderate the heat
threat somewhat, although heat-index values above 100F remain
possible in some locations during peak afternoon hours.

.LONG TERM....Tuesday through Saturday...

The long-term forecast remains generally on track. Surface winds
will remain light around Tuesday and Wednesday with an easterly
component, then shift southerly and increase to moderate for the
rest of the forecast period. The southerly component will likely
sustain an elevated heat risk during this time. Drier air will
filter in at the start of the workweek under easterly flow,
displacing the moisture plume related to Jerry. Patches of below-
normal to above-normal moisture will move over the islands Tuesday
through Wednesday.

Mid to upper level ridging will be present at the beginning of
the period, however, model guidance shows an upper-level low
approaching the Caribbean by midweek. The 500 mb temperatures will
become cooler, enhancing thunderstorm development each afternoon.
Model guidance indicates that PWAT values are forecast to
increase, particularly from Thursday through Saturday, as both
moisture from a frontal boundary approaches from the north and
southerly flow steers tropical moisture over the region. These
features may bring PWAT values above 2 inches by the end of the
forecast period which is considered above normal values.

At this time, flood risk remains limited on Tuesday and Wednesday,
but will likely increase to elevated levels from Thursday onward,
particularly during afternoon convection influenced by the
dominant winds, diurnal heating, sea breeze convergence, and local
effects. This means flooding in urban areas, roads, small streams,
and washes will remain in the forecast.


&&

.AVIATION...

(18Z)
Outer rainbands of TC Jerry will continue to produce
SHRA/TSRA this aftneve. TEMPO MVFR to brief IFR in heavy
SHRA/TSRA, mainly at TJSJ, TJPS, TIST, TJBQ psbl. Frequent
lightning and heavy rain may cause localized water on
ramps/runways with rapid CIGs/VIS changes. Late tonight, SHRA/VCTS
could affect TJPS/TIST/TISX terminals overnight. SSE 1015 kt
with sea-breeze variation; convective gusts to 2530 kt possible.
Winds turning light and variable aft 11/22z.

&&

.MARINE...

The Tropical Storm Jerry is located just a hundred miles
northeast of the area, which will continue to result in gentle to
light south winds across the region. Energy from the northerly
swell will continue to diminish across the offshore Atlantic
waters, leaving mostly seas up to 6 feet. Therefore, small craft
operators should exercise caution along the offshore Atlantic
waters and the Anegada Passage. External bands from Tropical Storm
Jerry will increase periods of showers and thunderstorms from its
outer bands, continuing today across portions of the waters.
Conditions are forecast to gradually improve on Sunday. &&

.BEACH FORECAST...

No changes to the inherited forecast. A moderate risk of rip
currents is in place tonight into tomorrow across beaches along
the northern, eastern, and southeastern coast of Puerto Rico,
Vieques, Culebra and the USVI. That means life-threatening rip
currents are possible in the surf zone and beachgoers need to
exercise caution. Over the coming days, similar conditions will
dominate. For more information, please refer to the Surf Zone
Forecast for Puerto Rico and the U.S. Virgin Islands (SRFSJU) or
visit weather.gov/beach.

&&

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

$$

SHORT TERM & AVIATION...CVB
LONG TERM....YZR
MARINE & BEACH FORECAST...LIS