FROM: NWS SJU
AREA: NWS SJU County Warning Area
SENT: 2026-07-29T07:13:00+00:00
Area Forecast Discussion: NWS SJU
000
FXCA62 TJSJ 290713
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
313 AM AST Wed Jul 29 2026
…New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER…
.KEY MESSAGES…
Issued at 313 AM AST Wed Jul 29 2026
* A Heat Advisory is in effect from 10 AM to 5 PM AST today for
coastal and urban areas of Puerto Rico and the U.S. Virgin
Islands, where dangerous heat indices are expected. Additional
Heat Advisories may be needed through the remainder of the week.
* Showers and thunderstorms will develop this afternoon, mainly
across the interior and northwestern portions of Puerto Rico.
Some storms may produce frequent lightning, strong wind gusts,
torrential rainfall, and localized flooding.
* A drier air mass accompanied by Saharan dust will gradually
overspread the region today and persist through at least Friday.
Expect hazy skies, reduced air quality, and temperatures
remaining above normal despite a decrease in overall rainfall
coverage.
* Another tropical wave may approach the region late this weekend
into early next week. Although forecast confidence remains low,
it could lead to increased showers and thunderstorms.
* Increasing easterly winds will continue to deteriorate marine
and beach conditions through the week, resulting in building
seas and a higher risk of life- threatening rip currents along
exposed beaches.
&&
.Short Term(Today through Friday)…
Issued at 313 AM AST Wed Jul 29 2026
The trailing moisture associated with a weak tropical wave
remains over the region overnight, with precipitable water (PWAT)
values ranging between 1.75 and 2.00 inches. However,
strengthening mid-level ridging over the northeastern Caribbean
continues to suppress widespread overnight convection, limiting
rainfall to a few passing showers across the local waters and
windward areas. Another warmer-than-normal night was observed
across Puerto Rico and the U.S. Virgin Islands, with minimum
temperatures remaining in the upper 70s to lower 80s across most
coastal and urban locations. Surface winds were generally from the
east to east-southeast at 5 to 15 mph, accompanied by typical
land-breeze variations.
Today, dangerous heat will remain the primary weather hazard
across Puerto Rico and the U.S. Virgin Islands. Consequently, a
Heat Advisory is in effect from 10 AM to 5 PM AST for coastal and
urban areas, where heat indices are expected to reach hazardous
levels, particularly in locations receiving little or no rainfall.
While low-level convergence may generate a few passing showers
across the U.S. Virgin Islands and eastern Puerto Rico during the
morning, much of the region is expected to remain mostly dry,
allowing temperatures to climb well above normal. Behind the
departing tropical moisture, a drier air mass accompanied by low
to moderate concentrations of Saharan dust will gradually
overspread the islands, leading to hazier skies and a
deterioration in air quality.
Despite the arrival of drier air, local effects will continue to
support afternoon convection. Under an east-southeast steering
flow, streamers developing downwind of the U.S. Virgin Islands,
Vieques, and the Luquillo Mountains may produce periods of
moderate rainfall before daytime heating, sea-breeze convergence,
and orographic lifting trigger scattered to numerous showers and
thunderstorms across the interior and western portions of Puerto
Rico. Some thunderstorms may become strong, producing torrential
rainfall, frequent lightning, gusty winds, and small hail.
Although the overall flooding threat remains limited, isolated
urban and small-stream flooding will be possible with heavier or
repeated storms.
An even drier air mass, accompanied by additional Saharan dust,
will overspread the region on Thursday and persist through at
least Friday. This pattern will favor hazy skies, degraded air
quality, and reduced overall shower coverage, while maintaining
above-normal temperatures. As a result, additional Heat Advisories
or other heat-related products may be required through the end of
the workweek. A weak wind perturbation moving through the local
area around Friday may briefly increase passing showers across
windward areas of Puerto Rico and the U.S. Virgin Islands before
typical afternoon convection redevelops over the interior and
western portions of Puerto Rico.
&&
.Long Term(Saturday through Wednesday)…
Issued at 313 AM AST Wed Jul 29 2026
A variable weather pattern continues for the long-term forecast
period. A strong surface high-pressure system located over the
central Atlantic will maintain breezy conditions under a
southeasterly wind flow through Monday. A tropical wave and an upper-
level low are approaching the local area early next week, increasing
moisture and instability across the northeastern Caribbean region.
The latest model guidance continues to suggest seasonal precipitable
water (PWAT) values between 1.60 and 1.80 inches on Saturday.
However, from early Sunday through late Monday, PWAT values will
gradually increase as the tropical wave and upper-level low position
over the region, bringing above-normal PWAT values of 2.00 to 2.10
inches. As the upper-level low arrives, cool mid-level temperatures
(around -6 to -7 degrees Celsius at 500 mb) combined with enhanced
lifting will promote cloud growth and atmospheric instability.
During this weather scenario, frequent passing showers are expected
across portions of eastern Puerto Rico and the U.S. Virgin Islands,
followed by afternoon convective activity across central and western
Puerto Rico. Showers and thunderstorms accompanied by frequent
lightning are anticipated during this period. Due to current drought
conditions, any rainfall will be beneficial for the islands
regardless of where it falls. Elevated temperatures will persist
throughout the perioddriven by normal to above-normal temperatures
at the 925 mb levelwith daytime highs reaching the upper 80s to low
90s across coastal and urban areas.
By Wednesday, another mid-to-upper-level low will approach the
region, further increasing instability and moisture. However,
uncertainty remains regarding exact impacts. Residents and visitors
are encouraged to stay informed and monitor weather updates as the
week progresses.
&&
.AVIATION…
(06Z TAFS)
Issued at 313 AM AST Wed Jul 29 2026
Mainly VFR conds will prevail through the period. SHRA/TSRA will
develop after 29/16Z across the interior and W PR, with TEMPO
MVFR/IFR conds possible at TJBQ due to +SHRA/TSRA, reduced vsbys,
mtn obscurations, and gusty outflow winds. ESE sfc winds 10-18 kt
with gusts up to 30 kt aft 29/13z, becoming light/vrb after
29/23Z. Stronger TSRA may produce gusts above 30 kt and frequent
lightning. Hazy skies will return later today.
&&
.MARINE…
Issued at 313 AM AST Wed Jul 29 2026
A surface high pressure continues to strengthen over the central
Atlantic, tightening the pressure gradient, promoting moderate to
locally fresh east to east-southeast for the next few days. These
conditions will maintain choppy seas across portions of the local
Atlantic and Caribbean waters, including the local passages.
Moderate concentrations of Saharan Dust will bring hazy skies and
slightly reduce visibility throughout the workweek.
&&
.BEACH FORECAST…
Issued at 313 AM AST Wed Jul 29 2026
The beach forecast remains on track. The moderate risk continues
across exposed beaches of northern and eastern Puerto Rico,
including Vieques and Culebra, and the U.S. Virgin Islands. As winds
continue to strengthen, the moderate risk will spread across southern
Puerto Rico, while the western beaches remain under a low risk.
Although the risk is not high, beachgoers should continue to
exercise caution as life-threatening rip currents remain possible
along the surf zone. The moderate risk should persist throughout the
workweek, but it may downgrade along southern beaches of Puerto Rico
and St. Thomas and St. John in the U.S. Virgin Islands as winds
weaken once again during the weekend. Nevertheless, beachgoers
should be aware of life-threatening rip currents in the vicinity of
jetties, groins, reefs, and piers. Besides rip currents, beachgoers
should stay weather alert as showers and isolated thunderstorms
could still be expected in the afternoons, particularly over
portions of western Puerto Rico.
&&
.FIRE WEATHER…
Issued at 313 AM AST Wed Jul 29 2026
Expect minimum relative humidity values near or above critical
thresholds today, critically dry fuels persist across southern
Puerto Rico and St. Croix. East-southeasterly winds are forecast
to become breezy to windy from today onward, which could promote
the spread of any fire that develops. Additionally, a drier
airmass accompanied by Saharan dust will spread over the region
later this afternoon. Residents and visitors should avoid outdoor
burning and exercise caution with activities that could generate
sparks or open flames. Fire weather partners should continue to
monitor the forecast.
&&
.SJU WATCHES/WARNINGS/ADVISORIES…
PR…Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for PRZ001>005-007-008-010>013.
VI…Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for VIZ001-002.
AM…None.
&&
$$
KEY MESSAGES/SHORT TERM/AVIATION/FIRE WEATHER…CAM
LONG TERM….GRS
MARINE/BEACH FORECAST…MNG
Alert Expiration: 2026-07-29T15:13:00+00:00
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