299
FXCA62 TJSJ 081838
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
238 PM AST Wed Oct 8 2025

.KEY MESSAGES...

* Lingering moisture, combined with sufficient instability, will
  continue to bring periods of heavy showers, thunderstorms, and
  gusty winds for the rest of this afternoon and again on Thursday.
  Flooding risks ranging from limited to elevated can be
  anticipated, with potential for urban and small stream flooding.

* Southerly wind flow will bring above-normal temperatures in
  combination with above-normal moisture, which could result in an
  elevated to significant heat threat through the end of the
  workweek.

* The National Hurricane Center (NHC) continues to monitor Tropical
  Storm Jerry, located over the central Atlantic. The system is
  expected to approach the northeast Caribbean by Friday.

* An extended wet period will continue into the weekend, as deep
  tropical moisture from Tropical Storm Jerry, moving north of the
  area, helps support rounds of showers and thunderstorms.

* Hazardous marine and beach conditions could be expected as swells
  from Jerry reach the regional waters by Friday and continue into
  the weekend.

* For the U.S. Virgin Islands, particularly St. Thomas and St. John,
  conditions could deteriorate more than in the rest of the forecast
  area as Tropical Storm Jerry passes to the northeast. Periods of
  gusty winds, rough seas, and locally heavy rainfall are possible
  from Friday into the weekend.

&&

.SHORT TERM...Tonight through Friday...

Weather conditions across Puerto Rico and the US Virgin Islands were
mostly calm early in the day, with clear to partly cloudy skies. The
most active weather occurred over the surrounding waters, where
strong showers and frequent lightning were observed during the
morning hours. After 10 AM, showers and isolated thunderstorms began
affecting the southern sections of Puerto Rico, gradually spreading
inland and eventually across northwestern Puerto Rico. These sky
conditions allowed temperatures to rise into the upper 80s to low
90s along coastal areas and the 70s to low 80s across the interior
and mountainous regions. The combination of warm temperatures and
lingering tropical moisture from a nearby wave elevated heat index
values to advisory levels, resulting in increased heat stress risks
for outdoor activities and indoor areas without proper air
circulation. Light and variable southeasterly winds contributed to
limited ventilation, further enhancing the heats impact across the
region. Overall, while the weather remained mostly fair for the
Virgin Islands and northern Puerto Rico, localized heavy showers
persisted, particularly across southern, interior, and northwestern
Puerto Rico, and for heat-related risks mainly over the northern and
western sections of PR.

Tonight, lingering moisture combined with the influence of an upper-
level trough will sustain shower and isolated thunderstorm activity
across the windward sectors of the islands. These features will
continue to provide sufficient instability for intermittent rainfall
and localized convection through the overnight hours and on
Thursday. Expect periods of heavy rainfall and thunderstorm
activity, mainly during the afternoon, across the interior and
northwestern portions of Puerto Rico. Light southeasterly winds will
persist, maintaining warm and humid conditions across the islands.

By late Friday into the weekend, weather, marine, and coastal
conditions will depend largely on the evolution of Tropical Storm
Jerry. According to the latest 11 AM bulletin from the National
Hurricane Center (NHC), Jerry is forecast to move northeast of the
local islands. The systems closest approach is expected to be
approximately 220 miles from Saint Thomas and Saint John, 230 miles
from Saint Croix, and 240 to 270 miles east-northeast of Puerto
Rico, including Vieques and Culebra.

Model guidance and NHC forecasts continue to indicate that the
system will remain northeast of the U.S. Virgin Islands. However,
outer rainbands and associated instability could enhance shower and
thunderstorm activity, particularly on Friday afternoon and during
the weekend.

Residents and visitors are urged to stay informed and monitor
official updates from the National Hurricane Center and the local
National Weather Service office in San Juan. The main threats
include lightning, gusty winds, and ponding of water on roadways,
with the potential for localized flooding and minor to isolated
flash flooding in areas of poor drainage or under persistent
rainfall.

.LONG TERM...Saturday through Wednesday...

.PREV DISCUSSION... /issued 538 AM AST Wed Oct 8 2025/

The forecast remains on track, with the arrival of trailing moisture
associated with Tropical Storm Jerry. Latest precipitable water
(PWAT) guidance indicates values above the normal climatological
range (2.25 to 2.50 inches) across the region. This suggests a wet
and moist pattern is likely from Saturday through at least Monday
across Puerto Rico and the U.S. Virgin Islands. As Tropical Storm
Jerry tracks north of the region, prevailing winds will initially be
southeasterly, then will shift from the southeast starting Sunday.

Showers and thunderstorms are expected this weekend, a result of the
high moisture environment combined with daytime heating and local
effects. While most of the area will experience some activity
associated with the system, the U.S. Virgin Islands are expected to
observe most of the activity due to their closer proximity to the
storm`s path. Portions of eastern Puerto Rico, Culebra, and Vieques
will also observe frequent showers. On Saturday, with winds
prevailing from the south, activity will be focused over central and
northern Puerto Rico, including the San Juan metro area, mainly
during the afternoon hours. From Sunday onward, as winds shift from
the southeast, the activity will primarily focus over central Puerto
Rico toward the northwestern quadrant of the island.

Under this persistent moist pattern, the risk of flooding remains
elevated through the beginning of the workweek. Additional hazards
include: urban and small stream flooding, minor flooding in low-
lying areas, quick river rises, the potential for landslides, and
frequent lightning.

Conditions are expected to improve quickly starting Tuesday as a
surface high-pressure system and a mid-level ridge settle over the
central Atlantic. This pattern will promote drier and more stable
atmospheric conditions through the end of the forecast period.

Residents and visitors are urged to continue monitoring the progress
of Tropical Storm Jerry and updates from the National Hurricane
Center and our local office as the system approaches the Lesser
Antilles.
&&

.AVIATION...
(18Z TAFs)

Most TAF site should remain with VFR cond. However, TJBQ could
experience brief periods of MVFR conditions and low VIS through
08/23Z, as available tropical moisture will continue to bring
SHRA/TSRA. TSRA activity will persist mostly over NW to
northcentral PR. USVI TAF sites could also observe SHRA/VCTS
particularly overnight. Sfc winds ESE 05-12 kt, with occasional
higher gusts psbl in/near SHRA/TSRA.

&&

.MARINE...

Moisture associated with a tropical wave will continue to influence
the local waters through tonight, maintaining scattered to numerous
showers and isolated thunderstorms. Attention then turns to Tropical
Storm Jerry, currently over the central Atlantic and forecast to
pass well northeast of the local islands by Friday. Although no
direct tropical storm impacts are expected, indirect marine impacts
will spread across the regional waters by Thursday night into the
weekend. Swells generated by Jerry will lead to hazardous seas up to
8 feet, particularly across the offshore Atlantic waters and the
Anegada Passage. Mariners should exercise caution, as conditions are
expected to deteriorate late Thursday night through the weekend
before gradually improving by early next week.

&&

.BEACH FORECAST...

A moderate to high risk of rip currents is likely along the north-
and east-facing beaches of Puerto Rico and the U.S. Virgin Islands
from Thursday through the weekend as swells from Tropical Storm
Jerry begin to affect the local waters. These swells will gradually
increase in height by Thursday night, leading to hazardous surf
conditions with breaking waves up to 7 feet along exposed beaches.
Beachgoers and visitors are urged to exercise extreme caution, heed
local advisories, and avoid swimming in high-risk areas, as life-
threatening rip currents are expected to persist through the weekend
before gradually improving early next week.

In addition, thunderstorms will pose significant hazards at the
coast. Frequent lightning strikes, gusty winds, and heavy rainfall
may lead to dangerous conditions, including sudden reductions in
visibility and localized flooding near the shoreline. Remember: if
thunder roars, go indoors. Swimmers and boaters should immediately
seek shelter when storms approach.

&&


.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>005-007-
     008-010-011.

VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION...MMC
MARINE/BEACH...CVB