080
FXCA62 TJSJ 011852
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
252 PM AST Fri Aug 1 2025

.KEY MESSAGES...

* A tropical wave will approach and affect the islands starting
  tonight into Saturday morning, increasing the frequency of
  showers and thunderstorms. Urban and small stream flooding and
  frequent lightning is expected to remain as the main hazards
  associated with this wave.

* Hot temperatures will continue to persist all weekend, with
  above normal temperatures and high heat indices.

* Low to moderate concentrations of Saharan dust will return by
  early next week, resulting in hazy skies and deteriorated air
  quality.

&&

.SHORT TERM...Tonight through Sunday...

Isolated to scattered showers affected portions of eastern Puerto
Rico and the U.S. Virgin Islands during the morning hours, leaving
minimal accumulations. Then, afternoon convective activity started
across portions of central and western Puerto Rico producing heavy
rainfall and thunderstorms. Doppler radar estimated between 1.0 to
2.0 inches of rain, in particular from Las Marias to Anasco. The "El
Yunque" streamer formed too, producing showers across portions from
Guaynabo to Vega Baja, with rainfall accumulations of 1.0 inch.
Today, maximum temperatures reached the upper 80s to low 90s,
particularly over the coastal and urban areas. The Luis Munoz Marin
Int. Airport reported a high of 90 degrees Fahrenheit. High heat
indices were observed as well, with values between 108 to 110
degrees Fahrenheit over northern and western Puerto Rico, and St.
Croix. A Heat Advisory was in effect for the aforementioned areas.

Weather conditions are expected to deteriorate tonight as a
tropical wave located east of the Lesser Antilles approaches the
region. The latest precipitable water content guidance suggest
values reaching the 2.25 to 2.30 inches by early Saturday. Given
the expected conditions, heavy rainfall and isolated thunderstorms
are expected from tonight through Saturday, mainly across
portions of eastern and northern Puerto Rico, and the U.S. Virgin
Islands. However, showers and thunderstorms are expected over
portions of western and central Puerto Rico are expected during
the afternoon hours. At this time there is an elevated risk of
flooding across Puerto Rico, where flooding in urban areas and
small streams is likely. In the other hand, the flooding risk is
limited for the U.S. Virgin Islands , where ponding of water and
minor flooding is possible. Residents and visitors, please be
aware of these conditions and plan accordingly if planning outdoor
events.

Hot temperatures will continue to persist all weekend, with above-
normal 925 mb temperatures. Daytime temperatures will continue to
reach the upper 80s to low 90s along the coastal and urban areas
each day with high heat indices due to the combination of sufficient
moisture, east to southeast winds and high temperatures.

.LONG TERM...Monday through Friday...
(from previous forecast discussion)

After the moisture field from the tropical wave departs on Monday, a
low to mid-level ridge builds, with a deep southeasterly wind flow
established. This will cause temperatures to soar, with elevated to
significant heat indices across the local islands. Saharan dust will
move in too, so hazy skies are anticipated too. Then, on Tuesday,
the winds will turn from the northeast as a trough moves north of
the region. This trough will not have too much moisture to work
with, but shallow patches of moisture will stream from the Atlantic
waters in to the local islands, while afternoon convection is
anticipated for the western Cordillera Central and southwestern
Puerto Rico.

By the middle and latter part of the week, the surface high will
reform across the western Atlantic, maintaining the trade winds out
of the or east-southeast at 15 to 20 mph. Moisture will be limited
to the lowest levels of the atmosphere, as dry air filter in at the
mid levels. In general, the weather will be typical, with passing
showers moving over the east of Puerto Rico and the Virgin Islands
in the morning, and showers and thunderstorms anticipated each
afternoon along the interior and western Puerto Rico. Heat indices
are likely to remain elevated for most of the period, with potential
heat advisories each day. With these high temperatures, individuals
sensitive to heat, especially those without effective cooling or
adequate hydration could be the most affected.

&&

.AVIATION...

Mostly VFR conds expected across all terminals during the forecast
period. A surface perturbation will produce SHRA/TSRA affecting
TJBQ thru 01/22Z. Then, an approaching tropical wave will move
into the region will result in SHRA and VCTS for TJSJ/TIST/TISX
aft 01/22-23Z, causing brief MVFR conds thru 02/13Z. ESE winds
will prevail at 10 kts or less aft 01/22Z, with higher gusts and
sea breeze variations.

&&

.MARINE...

A surface high-pressure system over the central Atlantic, combined
with a vigorous tropical wave, will promote moderate to locally
fresh winds over the next few days, maintaining choppy marine
conditions across portions of the local waters. From tonight into
the weekend, the tropical wave will increase the potential for
thunderstorms and contribute to localized hazardous marine
conditions.

&&

.BEACH FORECAST...

Winds out of the east southeast at 15 to 20 mph will maintain a
moderate rip current risk for the beaches facing the northern
coast of Puerto Rico, Vieques, Culebra, and Saint Croix.

A tropical wave will approach the region this weekend. Therefore, the
risk of lightning strikes will increase, since thunderstorms will
stream at times across the local beaches.

&&

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

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

$$

MRR/GRS