FROM: NWS SJU
AREA: NWS SJU County Warning Area
SENT: 2026-07-28T07:39:00+00:00
Area Forecast Discussion: NWS SJU
000
FXCA62 TJSJ 280739
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
339 AM AST Tue Jul 28 2026
…New KEY MESSAGES, SHORT TERM, LONG TERM, AVIATION, MARINE,
BEACH FORECAST, FIRE WEATHER…
.KEY MESSAGES…
Issued at 339 AM AST Tue Jul 28 2026
* A hot weather pattern continues today. A Heat Advisory remains
in effect for coastal and urban areas of Puerto Rico and the
U.S. Virgin Islands, where dangerous heat indices are expected.
* A tropical wave will bring periods of showers and thunderstorms
today. The U.S. Virgin Islands can expect passing showers moving
inland, while the greatest coverage of thunderstorms is
expected across the interior and western portions of Puerto
Rico. Heavy rainfall may lead to localized urban and small-
stream flooding.
* Drier weather returns from Wednesday afternoon onward. A drier
air mass, accompanied by Saharan dust, will overspread Puerto
Rico and the U.S. Virgin Islands through the end of the week,
reducing rainfall coverage while maintaining hot and hazy
conditions.
* Another tropical wave may approach the region late this
weekend. While it could increase the potential for showers and
thunderstorms, confidence in the timing and impacts remains low
at this time.
* Increasing winds will promote a moderate risk of life-
threatening rip currents along windward-facing beaches in Puerto
Rico and the U.S. Virgin Islands over the next several days.
&&
.Short Term(Today through Thursday)…
Issued at 339 AM AST Tue Jul 28 2026
Although the moisture field associated with a tropical wave
persisted across the region overnight, with precipitable water
(PWAT) values between 1.75 and 2.00 inches, increasing mid-level
ridging over the northeastern Caribbean was sufficient to suppress
widespread convection. As a result, skies remained mostly clear,
with only a few passing showers over the local Atlantic and
Caribbean waters and the windward locations. Another warmer-than-
normal night was observed across Puerto Rico and the U.S. Virgin
Islands, with minimum temperatures generally in the upper 70s to
lower 80s across coastal and urban areas. Surface winds remained
light to moderate from the east to east-southeast at 5 to 10 mph,
accompanied by typical land-breeze variations.
Today, the lingering tropical moisture, combined with another
warmer-than-normal day, will continue the dangerous heat pattern
across Puerto Rico and the U.S. Virgin Islands. Consequently, a
Heat Advisory remains in effect from 10 AM to 5 PM AST for coastal
and urban areas, where heat indices are likely to reach hazardous
levels, particularly in locations that receive little or no
rainfall.
Throughout the morning, low-level convergence will support a few
passing showers across the USVI and eastern PR. Local topographic
effects will likely enhance shower development downwind of the
U.S. Virgin Islands, Vieques, and the Luquillo Mountain Range,
resulting in streamers capable of producing periods of moderate to
locally heavy rainfall. By the afternoon, daytime heating, sea-
breeze convergence, and orographic lifting are expected to promote
scattered to numerous showers and thunderstorms across the
interior and western portions of Puerto Rico. There is a medium to
high probability that some thunderstorms will become strong,
producing torrential rainfall, frequent lightning, gusty winds,
without ruling out small hail (similar to activity observed on
Monday). Therefore, an elevated risk of urban and small-stream
flooding is expected, with isolated flash flooding possible where
storms repeatedly affect the same locations. Residents and
visitors should remain alert for rapidly changing weather
conditions and the potential issuance of additional short-fused
warnings or advisories.
By Wednesday, the trailing moisture associated with the tropical
wave will gradually shift west of the area as a drier air mass
accompanied by suspended Saharan dust overspreads the northeastern
Caribbean. Nevertheless, sufficient low-level moisture and daytime
instability will likely persist to support afternoon showers and
isolated thunderstorms, mainly across the interior and western
portions of Puerto Rico, where local effects will remain favorable
for convection. Dangerous heat conditions are expected to continue
across coastal and urban areas, particularly where rainfall is
limited. Model guidance indicates precipitable water values
decreasing to around 1.15 to 1.45 inches by Wednesday night and
Thursday, supporting a lower probability of widespread convection.
Periodic pulses of Saharan dust will also promote hazier skies
through the latter part of the week while limiting shower coverage
mainly to passing trade-wind showers and localized afternoon
convection over western Puerto Rico.
&&
.Long Term(Friday through Tuesday)…
Issued at 339 AM AST Tue Jul 28 2026
A variable weather pattern may be expected in the long-term
forecast. A surface high pressure over the Central Atlantic will
dominate most of the wind pattern, mainly from the ESE-SE through
most of the period, though it may become from the northeast by late
Monday night. Although conditions will remain breezy during the
upcoming weekend, winds may weaken by the end of the period.
Based on the latest model guidance, patches of moisture may
arrive by Friday morning, with isolated showers moving across the
regional waters and windward sections of the islands, followed by
afternoon convection over portions of northwestern Puerto Rico.
Although the latest model solution suggests an increase in low-
and mid-level moisture, lingering Saharan dust concentrations and
strong winds may not lead to significant flooding or lightning
threat. A similar weather pattern may repeat on Saturday, though a
drier slot may move across the CWA by the afternoon along with
ridging in the mid-levels that should limit shower activity and
lower flooding risk.
The weather pattern on Sunday and Monday may become slightly
unstable as a tropical wave and an upper-level low approach the
local area, introducing tropical moisture and instability across
the CWA. The latest global model solutions suggest an increase in
both low- to mid-level moisture (above 60 – 70%), cool mid-level
temperatures (500 mb temperatures between -6 and -7 degrees
Celsius), and enhanced lifting promoting cloud growth and
introducing instability, though they differ with timing. While the
latest deterministic guidance of the GFS suggests the bulk of
moisture arriving on Sunday afternoon into the evening, the ECMWF
delays the tropical wave until Monday morning. Although both
models position the upper-level low over Hispaniola early Monday
and suggest an increase in shower and thunderstorm activity, this
introduces uncertainty to the forecast. Another factor that
introduces uncertainty to the forecast is another plume of Saharan
dust accompanying the tropical wave, which may weaken it by the
time it moves across the area. Hence, the flooding threat will
remain limited for both days, particularly over
western/northwestern Puerto Rico due to the combination of
available moisture, daytime heating, and local effects.
Under an ESE-SE wind flow, warmer to hotter temperatures can be
expected across the CWA, particularly over urban and low-lying
areas. With the available moisture content, heat indices will likely
exceed 100 degrees Fahrenheit and affect most individuals,
particularly those without adequate hydration or effective cooling.
Therefore, the heat threat will remain elevated throughout the
forecast period; Heat Advisories may be issued if required.
&&
.AVIATION…
(06Z TAFS)
Issued at 339 AM AST Tue Jul 28 2026
VFR conds will prevail through much of the period. Passing SHRA
may bring brief MVFR cigs/vsbys to TIST/TISX and TJSJ after
28/10Z. SHRA/TSRA will increase after 28/16Z, with TEMPO MVFR/IFR
conds likely at TJBQ and possible at TJSJ due to +SHRA/TSRA,
reduced vsbys, mtn obscurations, and gusty outflow winds. ESE sfc
winds 10-15 kt with gusts up to 25 kt, becoming light/vrb after
28/23Z. Stronger TSRA may produce gusts above 30 kt and frequent
lightning.
&&
.MARINE…
Issued at 339 AM AST Tue Jul 28 2026
Abundant moisture associated with a passing tropical wave will
increase the potential for showers and thunderstorms through this
evening. Gentle to moderate east to east-southeast winds will
continue today across the region, becoming moderate to fresh by
later this afternoon into Wednesday as high pressure system
continues to strengthens over the Atlantic, tightening the
pressure gradient. These winds will maintain choppy seas across
portions of the Atlantic waters, offshore Caribbean waters, and
the local passages, with seas up to 6 feet expected in localized
areas from midweek through the weekend.
&&
.BEACH FORECAST…
Issued at 339 AM AST Tue Jul 28 2026
A moderate risk of rip currents is forecast across northern Puerto
Rico today. However, a low risk of rip currents is expected to
continue elsewhere as gentle to moderate winds continues to prevail
today. Caution is always recommended, as even when the risk is low,
life-threatening rip currents can occur near reefs, jetties, groins,
and piers. From this afternoon onwards, winds will continue to
increase as high pressure over the Atlantic strengthens from
Wednesday onwards, becoming breezy to locally windy. As a result,
the moderate risk of rip currents will expand to most beaches of
Puerto Rico and the U.S. Virgin Islands. Life-threatening rip
currents will remain possible, exercise caution.
Additionally, warm to hot conditions will prevail, mainly across
coastal and low-elevation areas. Stay hydrated and take frequent
breaks in the shade. Beachgoers should also remain alert for
thunderstorms.
&&
.FIRE WEATHER…
Issued at 339 AM AST Tue Jul 28 2026
Although increasing tropical moisture will keep minimum relative
humidity above critical thresholds in the short term, critically
dry fuels persist across southern Puerto Rico and St. Croix, with
Keetch-Byram Drought Index (KBDI) values remaining above critical
thresholds. At the same time, easterly winds are expected to
gradually increase during the next couple of days, which could
promote the spread of any fire that develops. Residents and
visitors should avoid outdoor burning and exercise caution with
activities that could generate sparks or open flames, particularly
across areas with critically dry vegetation.
&&
.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
MARINE/BEACH FORECAST….GRS
LONG TERM…MNG
Alert Expiration: 2026-07-28T15:39:00+00:00
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