916
FXCA62 TJSJ 020710
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
310 AM AST Sat Aug 2 2025

.KEY MESSAGES...

* A vigorous tropical wave will cross the region today, bringing
  periods of heavy showers and thunderstorms to the islands. Stay
  alert for lightning, sudden downpours, and the potential for
  localized flooding.

* Normal to above-normal temperatures, combined with high humidity,
  will result in persistently elevated heat index values, especially
  on Sunday. The heat threat could reach significant levels at times
  across lower elevations and urban areas, posing a concern for
  vulnerable populations such as the elderly, children, and those
  with pre-existing health conditions.

* Low to moderate concentrations of Saharan dust are expected to
  return from Sunday night into Monday, leading to hazy skies and
  deteriorating air quality.

&&

.SHORT TERM...Today through Monday...

As of tonight, the frequency of passing showers increased across the
local islands as a tropical wave continued to approach the region.
Rainfall accumulations from the initial bands of moisture ranged
between 0.05 and 0.15 inches, mainly across the U.S. Virgin Islands
and eastern Puerto Rico. The most intense rainfall and thunderstorm
activity developed over the Anegada Passage, prompting the issuance
of a Marine Weather Statement. Besides that, the minimum
temperatures ranged from the upper 70s to low 80s in coastal and
urban areas, and from the upper 60s to low 70s in rural and
mountainous regions. Winds were generally from the northeast at 5 to
10 mph, with occasional higher gusts near heavier showers.

As the tropical wave continues to move westward, deep tropical
moisture will persist across the region, with precipitable water
values expected to peak between 2.00 and 2.40 inches. This will
support frequent showers and isolated thunderstorms across the U.S.
Virgin Islands and eastern Puerto Rico through the early morning
hours. By the afternoon, additional convection is expected to
develop across central and northwestern Puerto Rico due to the
available moisture from the tropical wave, daytime heating, and
local effects. At this time, the ELEVATED flooding concerns with
urban and small stream flooding are likely, particularly in areas
with poor drainage or already saturated soils, for Puerto Rico,
Vieques, Culebra, and Saint Thomas. While, Saint Croix and
southwestern Puerto Rico has a limited flooding risk, with ponding
of water and minor flooding possible in low-lying or poorly drained
areas. Residents and visitors are advised to stay informed and plan
accordingly, especially when participating in outdoor activities
today. Additionally, conditions should remain hot and humid through
the weekend, with near to above-normal 925 mb temperatures. Daytime
highs will range from the upper 80s to low 90s in coastal and urban
areas, with heat indices reaching dangerous levels due to the
combination of high temperatures, moisture, and easterly winds.

By Monday, as the tropical wave exits the region, a strengthening
low- to mid-level ridge will establish a deep southeasterly wind
flow. This pattern will lead to even hotter conditions across the
local islands, with elevated to significant heat indices. In
addition, a plume of Saharan dust is expected to arrive, resulting
in hazy skies and drier conditions to start the workweek.

.LONG TERM...Tuesday through Saturday...

The long-term forecast begins with lingering instability aloft as an
upper-level low continues to exit the forecast area. Although cooler
500 mb temperatures will lead to steeper lapse rates, below-normal
moisture levels will somewhat limit shower activity across the
region. Nevertheless, surface heating, sea breeze convergence, and
orographic lifting will be sufficient to compensate for the reduced
moisture, resulting in afternoon convection over interior and
western portions of Puerto Rico. Elsewhere, lingering suspended
Saharan dust will lead to hazy skies and limited shower activity.

Dynamic instability will persist on Wednesday as an induced surface
trough moves westward and crosses the northeastern Caribbean. The
areal coverage of showers and thunderstorms is expected to increase
during this period, aided by near-normal moisture converging in the
region.

For the remainder of the long-term forecast, weather conditions will
be variable, with marginal instability. This will be due to a series
of weak troughs crossing the region, combined with below-to-near-
normal moisture content. Alternating periods of fair weather,
showers, and thunderstorm activity will follow the typical seasonal
weather pattern. Showers will move onshore at times over windward
coastal areas during the night and morning hours, while shower and
thunderstorm development is expected over the interior and western
portions of Puerto Rico during the afternoon. The southern coastal
areas of Puerto Rico are likely to continue experiencing abnormally
dry conditions throughout the period, with only occasional, isolated
showers, which are likely to be insufficient to bring significant
relief to the region.

The forecast period will also be characterized by hot temperatures,
as 925 mb temperatures fluctuate between near-normal and above
climatological normals. These above-normal temperatures, combined
with humid conditions, will result in persistently high heat index
values. As a result, Heat Advisories, or even Warnings, cannot be
ruled out throughout the period. Residents and visitors are advised
to stay hydrated, limit outdoor activities during peak heat hours,
and monitor official updates for potential heat-related alerts.


&&

.AVIATION...
[06Z TAF]

With the passage of the tropical wave, TSRA is anticipated to affect
TIST and TJSJ through at least 02/15, causing a brief period of MVFR
conditions with the heaviest Tstorm from time to time. Aft 02/17
SHRA/ ISOL TSRA could affect areas near the vicinity of TJBQ and
TJPS through 02/23z. Winds will gradually shift from the ENE to the
ESE as the wave moves across the islands.

&&

.MARINE...

A surface high-pressure over the central Atlantic, combined with a
vigorous tropical wave, will promote moderate to locally fresh winds
through the weekend. Seas of up to 7 ft are likely for the offshore
Atlantic waters where a Small Craft Advisory is in effect through
this evening. The tropical wave will continue to affect the regional
waters today, with lingering effects expected into tomorrow,
increasing the frequency of showers and thunderstorms throughout the
weekend. Hazy skies due to the arrival of Saharan dust are
anticipated on Monday.

&&

.BEACH FORECAST...

Shower and thunderstorm activity due to a tropical wave will
continue to affect some coastal areas of the islands on occasion
today. Periods of moderate to locally heavy rainfall and occasional
lightning strikes remain possible with this activity. Winds out of
the east northeast at 17 to 23 mph will maintain a moderate rip
current risk for the beaches facing the northern coast of Puerto
Rico, Culebra, and Saint Croix.

Given the potential for thunderstorms, beachgoers are advised to
take appropriate lightning safety precautions. Lightning can strike
with little warning, particularly near open water or along the
shoreline. At the first sign of thunder or lightning, all beach and
water activities should be stopped immediately. Seek shelter in a
well-constructed building or a hard-topped vehicle, and wait at
least 30 minutes after the last sound of thunder before resuming
outdoor activities.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory until 6 PM AST this evening for AMZ711.

&&

$$

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