903
FXCA62 TJSJ 220828
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
428 AM AST Tue Sep 22 2026

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 428 AM AST Tue Sep 22 2026

- A seasonal weather pattern is expected for the next couple of
  days across Puerto Rico and U.S. Virgin Islands, with afternoon
  convection mainly over interior, western and eastern Puerto
  Rico.

- Heat-related risks will continue each day, Wednesday being of
  the greatest concern. Heat-sensitive individuals should avoid
  outdoor activities and stay hydrated.

- A wetter pattern is expected from Thursday as a tropical wave
  approach the islands, increasing the chance of stronger shower
  and thunderstorm activity, especially in the afternoons.

- A low rip current risk will persist today; however, gentle to
  moderate winds will elevate the risk to moderate by Wednesday.

&&

.Short Term(Today through Thursday)...
Issued at 428 AM AST Tue Sep 22 2026

A seasonal weather pattern is expected today. Precipitable water
(PWAT) values ranging from seasonal to above-seasonal ranges will
allow morning showers to filter in during the morning over the
USVI and eastern interior portions. Light winds from an east-
southeasterly flow will promote shower and thunderstorm activity
during the afternoon, especially over the northwestern portions of
Puerto Rico. A couple of mid-to-upper-level lows approaching from
the northeast will promote seasonal 500-mb temperatures and
instability, which could result in stronger afternoon convection
over the CWA. This, combined with local effects and prevailing
light winds could allow shower and thunderstorm development over
most of the local area.

Moving into mid-week, a drier air will filter into the mid-
levels. Nonetheless, the aforementioned mid-to-upper-level lows
will linger in our vicinity for the rest of the short-term period,
which will continue to promote 500-mb temperatures around
seasonal values, even dropping below seasonal values by Thursday.
The drier air intrusion into the mid-levels should marginally
limit deep convection on Wednesday, however, low-level moisture
and local effects should still support afternoon convection mainly
over northwestern portions. By Thursday, moisture associated to a
tropical wave will reach the islands, increasing the potential
for deeper convection over eastern and western to northwestern
portions.

Overall, the primary weather hazards will include localized heavy
rainfall, and isolated thunderstorms, which could be accompanied
by frequent lightning and strong gusts. Light winds from an ESE
flow on Tuesday could lead to slow-moving storms that increase the
risk of excessive rainfall, particularly in the afternoon. A
limited to elevated risk of excessive rainfall is expected on
Tuesday, with more localized risks on Wednesday due to the drying
in the mid- levels, and return to limited to elevated levels on
Thursday as conditions become more favorable for stronger
convection. Consequently, these conditions may lead to water
ponding on roadways, urban and small stream flooding, and even
isolated flash floods in areas with an elevated risk level,
alongside a continued risk of landslides where terrain is already
saturated from recent rainfall.

An elevated excessive heat risk is likely on Wednesday as cloud
cover is anticipated to be less than on Tuesday and Thursday, for
which a limited level is expected.

&&

.Long Term(Friday through Tuesday)...
Issued at 428 AM AST Tue Sep 22 2026

The main synoptic features during the long term period are a couple
of multi level low pressure systems across the eastern Atlantic
Ocean that will promote an east-to-southeast wind flow across the
CWA. Winds are expected to bring calm-to-breezy conditions
throughout the region potentially favoring the ocasional development
of streamers from the US Virgin Islands, Vieques, Culebra and El
Yunque rainforest. Low-to-moderate concentrations of Saharan Dust
will filter by Friday onwards bringing PWAT values down to 1.2
inches during the weekend. Sensitive groups should remain alert as
air quality may deteriorate. PWAT values will return to seasonal
levels by Monday. The potential for rain each day is expected to be
focused on the northwestern side of Puerto Rico and will be driven
by local effects such as sea-breeze convergence, orographic effects
and diurnal heating.Besides the flooding risk, visitors and citizens
should experience periods of excessive heat threats. With humidity
values ranging around seasonal levels and 925mb temperatures being 2
standard deviations above the normal values, the extreme heat risk
remains elevated thruough Sunday across coastal, urban, and exposed
areas, with conditions expected to vary with cloud coverage. This
level of heat affects anyone without effective cooling and/or
adequate hydration. With impacts likely in some health systems, heat
sensitive industries and infrastructure. It is recommended that
individuals limit outdoor activities and remain hydrated. It is
recommended that individuals follow the instructions of health
officials and monitor the evolving weather conditions.

&&

.AVIATION...
(06Z TAFS)
Issued at 428 AM AST Tue Sep 22 2026

Mostly VFR. SHRA/TSRA increase aftn, mainly TJSJ/TJBQ, with VCTS
at TJPS. Brief MVFR/IFR possible in heavier SHRA/TSRA, with mtn
obscurations. VCSH lingers TJSJ/TIST/TISX ovrng into Wed.
Convection wanes late this eve, with VCSH lingering TJSJ/USVI
terminals. Winds LGT/VRB to calm, becoming E-ESE 10-15 kt with
higher gusts/sea breeze variations aftn, then LGT/VRB ovrng.

&&

.MARINE...
Issued at 428 AM AST Tue Sep 22 2026

A surface high pressure building from the north-central Atlantic
will promote light to moderate east to southeast winds through the
end of the week. Seas will continue today between 1 and 3 feet. A
small long-period northeasterly swell will reach the area late
Wednesday, and build seas between 3 to 4 feet across the Atlantic
and Caribbean waters, including the local passages. Afternoon
thunderstorms developing from the Atlantic and western coastal
waters of Puerto Rico may produce locally strong gusts, torrential
rainfall, and frequent lightning through the early evening hours
each day.

&&

.BEACH FORECAST...
Issued at 428 AM AST Tue Sep 22 2026

A low risk of rip currents is expected to continue across all
beaches of Puerto Rico and the U.S. Virgin Islands through at least
early Wednesday. However, even with a low risk, life-threatening rip
currents can occur near groins, jetties, reefs, and piers. From late
Wednesday onward, a moderate risk is expected to return across the
north and east-facing beaches of the islands, due to the arrival of
a small long-period northeasterly swell, and as winds increase
locally due to the sea breeze across the coastal waters.

&&

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

$$

EVE...DSR/MMC/RVM
MID...ICP/JCP