888
FXCA62 TJSJ 010756
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
356 AM AST Mon Sep 1 2025

.KEY MESSAGES...

* Another warm day expected across the islands and heat indices
   that could exacerbate heat-related illnesses and symptoms.

 * Afternoon convection is expected to produce thunderstorms
   today across the western interior sections of Puerto Rico.

 * A tropical wave, combined with an upper-level trough, will
  increase the potential for showers and thunderstorms from
  Saturday into Sunday, heightening the flood threat.

 * For the U.S. Virgin Islands, mostly variable weather
   conditions will persist with warm conditions through the
   upcoming weekend, when the arrival of a tropical wave will
   increase shower frequency across the islands.

&&

.SHORT TERM...Today through Wednesday...

Clear to partly cloudy skies prevailed across the islands during the
overnight hours. Scattered showers with isolated thunderstorms were
noted mainly across the regional waters, with a few moving briefly
over land areas between the USVI and eastern PR. Minimum
temperatures were from the upper-70s to low 80s across the lower
elevations of the islands to the upper-60s and mid-70s across the
higher elevations of Puerto Rico. The wind was light due to land
breeze variations.

A meandering weak TUTT-low north of the area will promote marginal
unstable conditions aloft during the next few days, but particularly
on Wednesday as it sinks further south, just to our northwest. This
will promote colder 500mb temperatures near -6C, which is in the
50th percentile of climatology. In terms of the available moisture
content, the precipitable water content is still expected to remain
at normal levels through the short-term period, but peaking just
below 2 inches by early Wednesday. At lower levels, the Azores High
and a front over the northwestern Atlantic will promote light to
moderate southeasterly winds through Wednesday. Therefore, a similar
weather pattern is expected each day, with strong thunderstorms
developing mainly over the northwestern quadrant of PR, with
isolated thunderstorms developing elsewhere over portions of the
Cordillera and downwind from el Yunque area into nearby
municipalities. These thunderstorms can produce quick urban and
small stream flooding, cloud to ground lightning, and gusty winds.
Across the USVI, shower activity will peak between Tuesday and
Wednesday morning, as a surge of moisture currently east of the
Windward Islands moves across the local area.

Meanwhile, the combination of dewpoints from the upper 70s and low
80s during the day and the light southeasterly winds will continue
to promote Heat Advisory to Extreme Heat Warning conditions across
most coastal areas of the islands through the forecast period and
before the onset of afternoon showers. Therefore, stay well-
hydrated, limit strenuous activities during peak heat hours, avoid
leaving children or pets inside vehicles, and wear lightweight,
loose-fitting, light-colored clothing.


.LONG TERM...Thursday through Monday...

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...
(06z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hour. However, afternoon TSRA could develop near
TJBQ/TJSJ between 01/17-23Z, causing tempo MVFR to brief IFR
conditions. Elsewhere, mostly VCSH expected. Southeast winds
expected between 10-15 kt with sea breeze variations and higher
gusts aft 01/14z.

&&

.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. 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 will increase the frequency of showers and
thunderstorms, resulting in localized hazardous marine conditions.

&&

.BEACH FORECAST...

Calm marine conditions will continue to result mostly in a low
risk of rip current along all the coastal areas across all the
islands. Therefore, coastal conditions are suitable for beachgoers
and visitors. Although conditions remain good stay alert to areas
not designated to beachgoers.

$$

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001>005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM & AVIATION...DS
LONG TERM & MARINE....LIS