548
FXCA62 TJSJ 090920
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
520 AM AST Thu Oct 9 2025

.KEY MESSAGES...

* Convective afternoon showers and thunderstorms are forecast
  mainly across interior, northern, and western Puerto Rico. Lines
  of convection are also possible downwind of the local islands
  and El Yunque.

* A Heat Advisory is in effect from 10 AM to 4 PM AST for coastal
  and urban areas of Puerto Rico, Vieques, Culebra, and the U.S.
  Virgin Islands.

* Tropical Storm Jerry is located around 470 miles SE of St.
  Croix. The system is expected to approach the northeast
  Caribbean by late tonight and tomorrow, with its closest
  approach at about 198 miles ENE of St. Thomas.

* Hazardous marine and beach conditions are forecast as swells
  from Jerry reach the regional waters by late tonight and
  continue into Saturday. A Small Craft Advisory is in effect for
  the offshore Atlantic Waters and Anegada Passage.

* Deep tropical moisture from Jerry will help support rounds of
  showers and thunderstorms.

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

&&

.SHORT TERM...Today through Saturday...

Mostly fair weather conditions prevailed overnight across the
forecast area. Radar and satellite imagery showed isolated showers
over the waters and the vicinity of the U.S. Virgin Islands, along
with just a few clouds. Radar estimates indicated minimal rainfall
amounts. Surface weather stations across the islands recorded low
temperatures in the mid-70s to low 80s in coastal and urban areas,
and in the mid to upper 60s across interior Puerto Rico.

Today, Thursday, another active afternoon in terms of rain is
expected. Current satellite-derived precipitable water (PWAT) values
range from approximately 2.00 to 2.20 inches. A weakening upper-
level trough will continue to exert a slight influence on the region
while shifting to the northwest, followed by the arrival of an upper-
level ridge. A limited to elevated flooding risk will persist this
afternoon, with convective showers and thunderstorms forecast across
interior, northern, and western Puerto Rico. Lines of convection are
also possible downwind of the local islands and El Yunque.

Winds are expected to be light and from the east-southeast today,
turning more northerly tonight due to the influence of Tropical
Storm Jerry. Temperatures at the 925 mb level will be about one
standard deviation above normal. Combined with available moisture,
this will maintain above-normal surface temperatures and elevated
heat indices. A Heat Advisory is in effect from 10 AM to 4 PM AST
for coastal and urban areas of Puerto Rico, Vieques, Culebra, and
the U.S. Virgin Islands.

By Friday and Saturday, unstable weather conditions will prevail,
mainly due to the evolution and track of Tropical Storm Jerry. Heavy
rainfall is forecast for the U.S. Virgin Islands through Saturday,
which could result in flooding, particularly in areas with steep
terrain. According to the latest 2 AM bulletin from the National
Hurricane Center (NHC), Jerry is forecast to pass northeast of the
local islands tomorrow as a Category 1 hurricane. We will experience
indirect impacts from this system, such as outer rainbands and
associated instability, which could enhance shower and thunderstorm
activity, especially on Friday afternoon and Saturday. For that
reason, an elevated flooding risk is expected across portions of
Puerto Rico and the U.S. Virgin Islands on both days.

Residents and visitors are encouraged to stay informed and monitor
official updates from the National Hurricane Center and the local
National Weather Service office in San Juan.

.LONG TERM...Sunday through Thursday...


The latest Advisory by the National Hurricane Center has Tropical
Storm Jerry, a hurricane by that time, about 740 miles north of
San Juan by Sunday. Moisture plume trailing Jerry will continue to
promote PWAT values generally at 2 to 2.3 inches, normal to above
normal values for this time of the year, through at least late
Monday, with deep moisture being present. On Monday above normal
moisture will gradually filter out to the west while drier air
filters in from the east. Steering flow will start southeasterly
on Sunday, gradually becoming more easterly on Monday. Patches of
below normal to above normal moisture will filter over the islands
Tuesday through Wednesday. Mid to upper level ridging will be
present for most of the period, however a deep level trough will
dig down towards the eastern Caribbean by Wednesday and Thursday.
Current model guidance has an increase in PWAT values once again
late Wednesday into Thursday as moisture from a frontal boundary
moves over the area bringing above 2 inches of PWAT to end the
forecast period. As a surface low moves towards the western
Atlantic and a high positions itself over the eastern Atlantic,
steering flow will become southeasterly on Tuesday, southerly to
southwesterly on Wednesday and southwesterly by Thursday. Flooding
risk remains, particularly during afternoon convection steered by
the dominant winds, due to diurnal heating, sea breeze
convergence and local effects, and due to the plumes of moisture
at the beginning and end of the forecast period. Southerly
component of the winds will also aid in sustaining a heat risk
during the period.


&&

.AVIATION...
(06Z TAFs)

VFR conditions should prevail this morning across most TAF sites.
VCSH are likely at USVI sites. After 17Z18Z, SHRA/TSRA developing
over the Cordillera will reach TAF sites, potentially causing
intermittent periods of MVFR conditions with reduced VIS through
09/22Z. E to SE winds at 8 to 10 knots are expected, with sea breeze
variations. Winds will decrease after 09/22Z, becoming light and
variable and rain chances increasing for the USVI sites overnight.


&&

.MARINE...

Tropical Storm Jerry is currently over the central Atlantic and
forecast to pass well northeast of the local islands by late tonight
into Friday. Although no direct tropical storm impacts are expected,
indirect marine impacts will spread across the regional waters by
late tonight night into the weekend. Swells generated by Jerry will
lead to hazardous seas up to 8 to 9 feet, particularly across the
offshore Atlantic waters and the Anegada Passage, where a Small
Craft Advisory will be in effect from late tonight through late
Friday night. Mariners should exercise caution, as conditions are
expected to deteriorate late tonight through early in the weekend
before gradually.

&&

.BEACH FORECAST...

A moderate risk of rip currents will be in effect today and tonight
for the northern and eastern beaches of Puerto Rico as well as
beaches of Culebra, Vieques and the USVI. From Friday and into the
weekend, a high risk of rip currents will prevail for those areas 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 6 to
7 feet along exposed beaches. Conditions are expected to gradually
improve to moderate conditions early next week.

Heed the advice of lifeguards, beach patrol flags and signs. If you
become caught in a rip current, yell for help. Remain calm, do not
exhaust yourself and stay afloat while waiting for help. If you have
to swim out of a rip current, swim parallel to shore and back toward
the beach when possible. Do not attempt to swim directly against a
rip current as you will tire quickly.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for PRZ001>005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for VIZ001-002.

AM...Small Craft Advisory from midnight tonight to 6 AM AST Saturday
     for AMZ711-723.

&&

$$

YZR/MRR