882
FXCA62 TJSJ 030732
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
332 AM AST Sun Aug 3 2025

.KEY MESSAGES...

* Lingering moisture from the departing tropical wave will persist
  today, supporting the potential for afternoon showers and
  thunderstorms. This may result in a limited to elevated
  flooding threat, particularly across the interior and western
  portions of Puerto Rico.

* Humid conditions associated with the departing tropical wave,
  combined with hot surface temperatures, will result in an elevated
  to significant heat threat. As a result, Extreme Heat Warnings and
  Heat Advisories have been issued for portions of the region.

* Hazy skies are expected starting tonight into Monday due to the
  arrival of Saharan dust, which may lead to reduced visibility
  and deteriorated air quality.

&&

.SHORT TERM...Today through Tuesday...

Showers and thunderstorms associated to a departing tropical wave
continued to stream into the southern and eastern portions of Puerto
and the Virgin Islands during the night hours. These showers led to
lightning strikes and wind gusts, and brief periods of heavy rain.
The moisture field associated with the wave will gradually depart on
Sunday, while a surface high pressure centered a couple of hundred
miles northeast of the islands maintain a deep-layered southeast
flow. Rainfall activity is not expected to be as frequent or strong
as it was registered on Saturday, but some showers will continue to
reach the Virgin Islands and southeastern Puerto Rico at times. The
heaviest activity, as usual, is expected for the northwest corner of
PR. If enough sunshine is available, it will likely be very hot,
with heat indices above 105 for many coastal and urban areas.

On Monday, as Saharan dust arrives, skies will become hazy, and
rainfall probability will decrease. However, an approaching upper
level trough will increase instability aloft, and cooling down the
mid-levels of the atmosphere. Therefore, even if the rain is only
concentrated in the northwest, there is going to be an enhanced risk
of lightning and gusty winds. Then, on Tuesday, an induced surface
trough will shift the winds from the northeast. As a result,
temperatures are expected to cool down a bit, although still
seasonably hot. Chances of rain are higher for the southwest in the
afternoon hours, but passing showers will also become more frequent
in the local Atlantic waters and the northeast, as well as across
the Virgin Islands.

.LONG TERM...Wednesday through Sunday...

For midweek next week into the early part of the weekend, weather
conditions are forecast to be relatively variable. Any shower and
thunderstorm activity will follow a typical seasonal pattern.
Wednesday will begin with above-normal columnar moisture and
marginal instability aloft. Passing showers will affect windward
coastal areas during the morning, followed by deeper convective
activity in the afternoon as the above-normal moisture combines with
surface heating, sea breeze convergence, and local effects. This
activity could lead to urban and small stream flooding, primarily
across the interior and western portions of Puerto Rico. On Thursday
and Friday, the areal coverage of showers is expected to decrease
due to mid-level dry air intrusion and decreasing low-level moisture
to below-normal levels, which will increase atmospheric stability.
While shower and thunderstorm activity will follow a similar pattern
to Wednesday, areal coverage is expected to be more limited.

During this period, model guidance suggests that 925 mb temperatures
will fluctuate near or above climatological normals. This will
result in hot surface temperatures, which, when combined with
sufficient low-level moisture, will lead to heat index values
exceeding 100F. As a result, at least a limited to elevated heat
threat is expected to impact coastal and urban areas, particularly
on Thursday. A localized significant heat threat during peak daytime
hours cannot be ruled out.

For the weekend, discrepancies begin to emerge in global model
guidance regarding the evolution of a tropical wave. Both the GFS
and ECMWF suggest increasing instability aloft due to the approach
of a Tropical Upper Tropospheric Trough (TUTT) north of the forecast
area. However, by the end of the weekend, the GFS depicts a vigorous
tropical wave combining with this instability as it approaches the
northeastern Caribbean. This scenario would result in a gradual
deterioration of weather conditions and an increased flooding threat
across the islands. In contrast, the ECMWF suggests some tropical
development of the wave, steering it northward before reaching the
Caribbean. Under this scenario, wetter conditions would be delayed,
and a more seasonal weather pattern would persist across the area.
Given the current uncertainty in model solutions, it is still too
early to determine any specific impacts for the region. Residents
are encouraged to stay alert and continue monitoring the forecast as
we move closer to the weekend.


&&

.AVIATION...
[06Z TAF]

Mainly VFR conditions expected to prevail. SHRA and TSRA are
expected to continue across the local waters, occasionally reaching
the USVI terminals and TJPS. From 17-21Z, TSRA expected for TJBQ,
with periods of reduced VIS and low ceilings. Winds are from the SE
AT 12-18 kts, with stronger gusts, especially near thunderstorms.

&&

.MARINE...

Trailing moisture from the tropical wave will continue to move over
the islands during the day. A surface high-pressure over the central
Atlantic will promote moderate to locally fresh winds through early
this week. Hazy skies are anticipated tonight into Monday due to the
arrival of Saharan dust.

&&

.BEACH FORECAST...

Moderate rip current risk continues today for the northern and
eastern exposed beaches of Puerto Rico, including Culebra and St.
Croix. This means that life-threatening rip currents are possible,
particularly near breaking waves and narrow channels. Swimmers and
beachgoers are advised to use caution, especially if unfamiliar with
local beach conditions.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning from 10 AM this morning to 4 PM AST this
     afternoon for PRZ001>005-007-008-010-011.

     Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for PRZ012-013.

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

AM...None.
&&

$$

SHORT TERM/AVIATION...ERG
LONG TERM/MARINE/BEACH...CVB