385
FXCA62 TJSJ 031829
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
229 PM AST Thu Jul 3 2025

.KEY MESSAGES...

 * Saharan dust will persist across the region through at least
   early Monday.

 * A tropical wave will approach the area by tomorrow.

 * The rip current risk will become low from tomorrow onwards.

&&

.SHORT TERM...Tonight through Saturday...

Mostly calm weather conditions prevailed across the U.S. Virgin
Islands and Puerto Rico today, with streamer-induced showers
developing from Culebra and Vieques, affecting parts of the San Juan
metropolitan area by the late morning. During the afternoon, diurnal
heating and local effects allowed convection over northwestern
Puerto Rico. Winds were generally from the east-southeast at 11 to
16 mph, with occasional higher gusts. Temperatures reached the upper
80s to low 90s in coastal and urban areas, while higher elevations
and rural zones stayed in the upper 70s to low 80s.

Looking ahead, models continue to indicate a weak tropical wave
approaching the region by Friday (4th of July Holiday). Although the
core of the wave is expected to remain south of Puerto Rico and the
U.S. Virgin Islands, enhanced moisture will move across the area.
This will support scattered showers throughout the day, with
afternoon convection likely across eastern Puerto Rico, the
interior, and western areas. A dense plume of Saharan dust is
forecast to gradually arrive by Friday afternoon, bringing moderate
to high concentrations across the region through the weekend. As a
result, limited deep rainfall development, hazy skies, reduced
visibility, and a decline in air quality are expected. Individuals
with respiratory conditions should closely follow Department of
Health guidance to avoid exacerbating symptoms. Temperatures will
continue to trend above normal, with heat indices expected to reach
heat advisory criteria, particularly in coastal and urban areas.
Therefore, residents and visitors are advised to stay well hydrated,
wear lightweight and breathable clothing, and avoid prolonged
exposure to the sun by taking frequent breaks in shaded or air-
conditioned areas. These precautions are especially important for
those participating in outdoor activities, as the combination of
high heat and dusty conditions can increase the risk of heat-related
illnesses and respiratory discomfort.

Overall, some low-level moisture will be embedded in the dust.
Therefore, the holiday weekend will not be completely dry.

.LONG TERM...Sunday through Thursday....

A relatively variable weather pattern is forecast across the
region from Sunday through Thursday, influenced by several upper-
level features, surface patterns, and an intrusion of Saharan dust
by the beginning of the period. On Sunday, there will be a slight
presence of instability aloft due to a cut-off low located over
Hispaniola that might result in moisture advection across the
area. Meanwhile, at the mid-levels (500700 MB), a ridge will help
maintain a relatively stable environment aloft. At the same time,
a plume of Saharan dust is expected to move over the region, with
concentrations capable of reducing visibility between 0.20 and
0.30 inches, resulting in hazy skies and possible air quality
deterioration. Overall, Sunday appears to be a quiet day with hazy
skies and limited shower development. However, daytime heating
and the local mountains will lead to the development of afternoon
convection, particularly in the interior and western parts of
Puerto Rico. Similar activity will be possible for the U.S. Virgin
Islands in isolated areas, mostly in the evening hours.

By Monday, another cut-off low will migrate from the northeast
into the northern portion of the region, further increasing
moisture levels and cloudiness. This upper-level feature will
enhance patches of cloudiness and moisture, which will be
transported westward by the prevailing easterly trade winds. The
interaction between this feature, surface heating, and local
effects will result in scattered showers and isolated afternoon
thunderstorms, mainly over the interior and western sections of
Puerto Rico each day. Trade winds will persist from the east under
the influence of a broad surface high pressure system stall over
the central Atlantic. On Thursday, the pattern will remain
similar, with southeast winds gradually taking hold as a broad
surface high over the central Atlantic extends further into the
Caribbean. Days will remain variable, with occasional passing
showers in the trade wind flow during the morning and overnight
hours, followed by pockets of afternoon convection over interior
and western Puerto Rico. So far today, although model had some
high level of uncertainty, Wednesday into Thursday will be the
most unstable days for the long term period.

&&

.AVIATION...
(18Z TAFS)

VFR conditions across most TAF sites. SHRA/TSRA will continue across
interior and northwestern PR through 03/20Z, with brief periods of
low ceilings and reduced VIS  possible at TJBQ. Showers will
diminish after 03/23Z. E-SE winds around 5-8 kts after will prevail
after 23Z, increasing after 04/13Z to around 10-15 kts, with
stronger gusts near the heaviest shower activity.

&&

.MARINE...

A broad surface high pressure over the central Atlantic will
continue to result in moderate to fresh easterly winds across the
region. Therefore, wind-driven seas will result in choppy marine
conditions across the Atlantic waters and the Caribbean Waters.
Saharan dust particles will be in place, resulting in hazy skies
and limited shower activity until Friday, when another tropical
wave moves into the islands, bringing showers and thunderstorms.

&&

.BEACH FORECAST...

The rip current risk will become low by Friday and will remain
like it through the weekend.

&&

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

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

$$

SHORT TERM/AVIATION...MMC
LONG TERM...LIS
PUBLIC DESK...CVB