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509
FXCA62 TJSJ 281900
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
300 PM AST Tue Jul 28 2026

...New SHORT TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER...

.KEY MESSAGES...
Issued at 254 PM AST Tue Jul 28 2026

- A Heat Advisory remains in effect through 5 PM AST for coastal and
  urban areas of Puerto Rico and the U.S. Virgin Islands, where
  dangerous heat indices are expected. High heat indices are
  expected to continue each late morning to afternoon during the
  next several days.

- Showers and t-storms are forecast to continue developing this
  afternoon under east-southeast flow. In the meantime generally
  moderate concentrations of Saharan Dust will continue moving
  westward over the region.

- A drier air mass, accompanied by additional Saharan dust, will
  move over the region tomorrow afternoon onwards through the end
  of the week, reducing rainfall coverage while maintaining hot
  and hazy conditions and increasing the fire weather risk.

- Increasing winds will promote up to a moderate risk of life-
  threatening rip currents along the beaches of Puerto Rico and
  the U.S. Virgin Islands through the rest of the week.

- 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.

&&

.Short Term(This evening through Thursday)...
Issued at 254 PM AST Tue Jul 28 2026

Mainly fair weather conditions have prevailed across the forecast
area throughout the morning hours. An elevated heat risk has
persisted due to the combination of hot temperatures and high
humidity, allowing heat indices across urban and coastal areas of
the islands to reach levels that can affect most individuals
sensitive to heat. Take the necessary precautions, particularly if
spending prolonged periods of time outdoors during the peak
heating hours. As a note, a record high temperature of 93F was
set today at the San Juan Area, specifically at the Luis Munoz
Marin International Airport climate station. This breaks the
previous record of 92F set in 1981. Winds have generally ranged
between 10 and 15 mph, with occasional higher gusts.

For the rest of the afternoon, convective activity driven by daytime
heating, sea-breeze convergence, and orographic effects is expected
to develop across the north-central and west-central to northwestern
municipalities of Puerto Rico. This will result in a limited to
elevated flood risk, with the potential for ponding of water on
roads and localized flooding in urban areas, roads, and in small
streams.

Tonight into Wednesday, as the Atlantic high-pressure system
continues to strengthen, the pressure gradient will tighten,
bringing breezy to windy conditions, with the strongest winds
expected between Wednesday and Thursday. In addition, the trailing
moisture associated with the tropical wave will gradually shift west
of the area as a drier air mass, accompanied by low to moderate
concentrations of Saharan dust, spreads across the region. These
particulates are expected to remain present through the rest of the
forecast period. Nevertheless, available low-level moisture and
daytime heating will continue to support afternoon showers and
isolated thunderstorms, mainly across the northwestern quadrant of
Puerto Rico. The flood risk will remain limited. By Thursday, the
latest model guidance remains consistent, indicating that
precipitable water values will remain below 1.5 inches, which is
below the climatological normal (around the 25th percentile). As a
result, the potential for widespread convection will be lower.

For the remainder of the short-term forecast period, although drier
air will continue to spread across the region, warm to hot
conditions will persist across coastal and urban areas, as reflected
by above-normal 925-mb temperatures. Residents and visitors are
encouraged to stay hydrated and take the necessary precautions to
minimize heat-related impacts.

&&

...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...
(18Z TAFS)
Issued at 254 PM AST Tue Jul 28 2026

Mainly VFR conditions across most TAF sites during this forecast
period. Except in TJBQ where VCTS/TSRA will remain more probable
from 28/18-21Z. This will likely result in intermittent MVFR
conds. Low to moderate concentrations of Saharan dust spreading
across the region will result in slightly VIS reductions from this
afternoon into the coming days. Another aviation concern will be
the winds which are expected to increase, with gusts near 30kts
after 29/13- 14Z through 29/23Z.

&&

.MARINE...
Issued at 254 PM AST Tue Jul 28 2026

Moisture associated with a tropical wave will start to depart the
local waters tomorrow afternoon, as drier air with Saharan Dust
takes its place. East to east-southeast flow will become more
moderate to fresh by later this afternoon into Wednesday as a high
pressure system continues to strengthen 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, through the weekend.

&&

.BEACH FORECAST...
Issued at 254 PM AST Tue Jul 28 2026

Up to a moderate risk of rip currents (life-threatening rip currents
are possible in the surf zone) is forecast across northern Puerto
Rico tonight. A low risk of rip currents is expected to continue
elsewhere, however, life-threatening rip currents often occur in
the vicinity of groins, jetties, reefs, and piers. High pressure
over the Atlantic will strengthen, causing winds to continue
increasing this afternoon and maintaining breezy to locally windy
conditions through the remainder of the week. Consequently, a
moderate risk of rip currents will affect most beaches across
Puerto Rico and the U.S. Virgin Islands. Furthermore, coastal and
low-elevation sectors will experience prevailing warm to hot
conditions. It is advised to stay hydrated and take regular breaks
in shaded areas.

&&

.FIRE WEATHER...
Issued at 254 PM AST Tue Jul 28 2026

Surface station have been reporting minimum relative humidity
values near or above critical thresholds today, critically dry
fuels persist across southern Puerto Rico and St. Croix. Easterly
winds are forecast to become breezy to windy, particularly
Wednesday and Thursday, which could promote the spread of any fire
that develops. Additionally, a drier airmass accompanied by
Saharan dust will spread over the region. 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 until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM/AVIATION/FIRE...YZR
LONG TERM...MNG
MARINE/BEACH FORECAST/KEY MESSAGES...MRR

NWS SJU Office Area Forecast Discussion