790
FXCA62 TJSJ 011822
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
222 PM AST Mon Sep 1 2025

.KEY MESSAGES...

* Residents and visitors in the US Virgin Islands and Puerto Rico
  can expect heat index values above 102 degrees Fahrenheit
  through much of the workweek, which could exacerbate heat-
  related illnesses and symptoms.

* Beachgoers in the US Virgin Islands and Puerto Rico will observe
  a low risk of rip currents through at least Saturday.

* Strong afternoon thunderstorms will develop each day across
  portions of PR and in the form of streamers downwind from the
  USVI.

* The National Hurricane Center is monitoring a tropical wave near
  Africa, which has a low chance (10 percent) of developing into
  a tropical cyclone within the next 48 hours and a moderate
  chance (50 percent) within the next 7 days.

&&

.SHORT TERM...Tonight through Wednesday

Another warm day when the US Virgin Islands and Puerto Rico
weather network detected heat index values mainly between 105
and 111 degrees Fahrenheit after mid-morning into the afternoon.
Skies were mostly clear early in the morning, slowly turning
partly cloudy to mostly cloudy at some locations, due to
orographic effects and excessive heating. Afternoon convection
developed downwind from St Croix into the surrounding waters and
from La Sierra de Luquillo into the San Juan Metropolitan areas.
Additionally, we noted thunderstorms developing along and west of
the Cordillera Central. Winds were mainly from the east-southeast
at 10 to 15 mph, with higher gusts and fluctuations due to sea
breezes.

The potential for strong afternoon convection is present in the
region due to the proximity of a mid-to-upper-level trough,
combined with local effects and diurnal heating. Thus, expect
periods of downpours producing localized flooding, frequent
lightning, and gusty winds through this evening for the western
parts of PR. In contrast, the US Virgin Islands will experience a
mixture of clouds and mostly clear skies, with a warm to hot rest
of the afternoon, followed by above-normal overnight temperatures,
accompanied by the arrival of some isolated, occasional showers.

On Tuesday, a surface disturbance is expected to bring more
frequent showers across the US Virgin Islands and eastern PR
around sunrise and the morning of Tuesday. As it interacts with a
mid-to-upper-level trough, we can expect the enhancement of
afternoon convection, which could result in an elevated risk of
flooding rains. Meanwhile, a similar weather pattern to today is
likely to return on Wednesday.

.LONG TERM...Thursday through Monday
PREV DISCUSSION... /issued 356 AM AST Mon Sep 1 2025/

The long term forecast starts with a variable pattern across
Puerto Rico and the U.S. Virgin Islands. At the surface, from
Thursday through Friday, weather conditions will be dominated by
high pressure over the central Atlantic, promoting an east-
southeast wind flow across the region. This pattern will allow
patches of tropical moisture with precipitable water values
ranging from 1.70 to 1.90 inches to stream across the islands. As
a result, variable conditions are expected during the mornings,
followed by the development of afternoon showers and thunderstorms
across the interior and northwest Puerto Rico, where the
combination of sea breeze convergence and daytime heating will
enhance convective development. Isolated thunderstorms cannot be
ruled out across the Virgin Islands and eastern Puerto Rico. By
late Friday and continuing into the weekend, an upper-level trough
near 250 mb will increase instability across the region, favoring
stronger convection with frequent lightning, gusty winds, and
periods of heavy rainfall.

As the weekend progresses, a tropical wave will further enhance
the moisture field across the islands from Saturday into Sunday,
resulting in more widespread shower and thunderstorm activity.
Rainfall is expected to begin early in the morning hours on
Saturday, becoming more active and widespread during the afternoon
over much of Puerto Rico, with isolated thunderstorms likely
elsewhere. This activity may lead to an increased risk of urban
and small stream flooding, especially in areas that experience the
heaviest rainfall. By late Sunday into Monday, drier air is
forecast to filter into the region as upper-level high pressure
erodes the trough aloft. This will promote greater stability,
warmer mid-level temperatures near 500 mb, and a noticeable
reduction in shower frequency, with mainly localized afternoon
showers expected over western Puerto Rico while the Virgin Islands
experience fair weather conditions.

&&

.AVIATION...
(18z TAFs)

Mostly VFR conds across all terminals, with possible VCSH over ISX
and IST and VCTS for JSJ and JPS this aftn. -TSRA/+TSRA is likely
for JBQ btwn 01/18-01/21z, with CIGs/VIS reducing and tempo MVFR/IFR
conds. SE winds btwn 11 - 15 kt will continue through 01/23z, with
gusts up to 20 - 22 kt over JSJ, JPS, and JBQ, reducing to 3 - 6 kt.
Winds should increase to 10 - 15 kt by 02/12 - 02/14z.

&&

.MARINE...

A surface high pressure over the central Atlantic and a surface
trough will continue to result in moderate to locally fresh east
to southeasterly winds across the local waters, producing moderate
chops to localized choppy seas. Seas will remain up to 5 feet
across the Atlantic offshore waters and even lower across the
coastal waters. For the upcoming weekend, the arrival of a
tropical wave is expected to increase the frequency of showers
and thunderstorms, potentially resulting in localized hazardous
marine conditions.

&&

.BEACH FORECAST...

The risk of rip currents will remain low in Puerto Rico and the
US Virgin Islands through at least Saturday. Be aware that
thunderstorms may impact the western and northern regions of
Puerto Rico through this evening.

Although the overall risk of rip currents is expected to remain
low during the forecast period, isolated but stronger rip currents
may occur in specific areas, especially near piers, jetties, and
channels.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

MORNING CREW...CAM/MNG
EVENING CREW...ICP/YZR