284
FXCA62 TJSJ 221903
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
303 PM AST Wed Jul 22 2026

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 300 PM AST Wed Jul 22 2026

* Showers and thunderstorms will continue to develop this
  afternoon, especially across the interior and western Puerto
  Rico. Brief gusty winds, frequent lightning, and an elevated
  risk of urban and small stream flooding are expected.

* Hot temperatures and elevated heat risks will persist through
  at least Friday, particularly across urban areas and lower
  elevations of Puerto Rico and the U.S. Virgin Islands.

* Moderate Saharan dust concentrations will begin arriving late
  Thursday, leading to hazy skies, reduced air quality, and lower
  visibility through the end of the week.

* We continue to monitor a tropical wave expected to approach the
  region on Sunday. While forecast confidence remains moderate,
  the system could bring beneficial rainfall to Puerto Rico and
  the U.S. Virgin Islands early next week.

&&

.Short Term(This evening through Friday)...
Issued at 300 PM AST Wed Jul 22 2026

The departing surface trough promoted an east-southeast wind flow
and another round of showers and thunderstorms east, south, and
southeast of Puerto Rico and the U.S. Virgin Islands this morning,
producing locally heavy rainfall and ponding of water in some
areas. By the afternoon, the activity moved into the interior and
western portions of PR, where we issued Flood Advisories and
Special Weather Statements. The local meteorological network has
consistently reported a limited risk of heat, so we decided to
cancel it. Meanwhile, the maximum temperatures in PR and the USVI
reached mainly in the mid and upper 80s, with some stations
reaching the low 90s. Winds in general were out from the east-
southeast at 5 to 15 mph, with Buck Island station at St Thomas
around 18 mph.

Additional showers and isolated thunderstorms will remain
possible through this evening, particularly across the U.S. Virgin
Islands, Vieques, Culebra, and portions of eastern and southern
Puerto Rico. Locally heavy rainfall may lead to ponding of water
on roadways and localized urban and small-stream flooding. A drier
air mass will gradually filter into the region overnight. At the
same time, another pulse of Saharan Air Layer (SAL) dust arrives
late tonight into early Thursday, resulting in moderate dust
concentrations, hazy skies, and deteriorating air quality.

Hotter-than-normal conditions will persist through Friday as the
drier air mass, subsidence aloft, and increasing Saharan dust
limit shower activity. Attention then turns to a weak tropical
wave forecast to approach the region around Friday morning.
Although the wave is embedded within a broad area of dry air that
should limit its organization, it will likely provide enough low-
level moisture to briefly raise precipitable water values to
around 2.00 inches and weaken the mid-level cap. This pattern
should support a return to a more typical summertime regime, with
passing morning showers affecting the U.S. Virgin Islands and
eastern Puerto Rico, followed by afternoon showers and isolated
thunderstorms developing across the interior and western sections
of Puerto Rico. Forecast confidence remains moderate, and the wave
will continue to be monitored as it could bring beneficial
rainfall to the islands early next week.

&&

.Long Term(Saturday through Wednesday)...
Issued at 357 AM AST Wed Jul 22 2026

A surface high pressure over the Atlantic will generally dominate
during the period with lows staying mainly over the western to
northern Atlantic, this will promote breezy easterly flow on
Saturday and east-southeasterly flow late Sunday onwards, with
breezy conditions persisting at least through the weekend.
However, most available moisture will remain below 800 mb through
Sunday afternoon with precipitable water (PWAT) values staying
below normal to normal range, with above normal values possible
during afternoon convection. Temperatures at 500 mb will remain
around -7 to -8 C, at normal to below normal, and will support
isolated t-storms associated with afternoon convection (due to
diurnal heating, sea breeze convergence and local effects).
Showers will also be steered towards the islands from time to time
especially during the morning and night hours, however a limited
flooding risk can occur mainly during afternoon convection over
interior to W and NW Puerto Rico.

Looking ahead from late Sunday into Wednesday, recent model guidance
indicates a tropical wave-driven moisture surge will affect the
region, with PWAT levels to normal and above-normal thresholds.
Furthermore, an upper-level low positioned over the islands from
Saturday through Monday will maintain lower 250 mb heights and
cooler 500 mb temperatures with both trending near or below seasonal
norms. Available moisture will in turn reach the mid to upper levels
through at least early Wednesday. These factors combined will foster
more favorable upper-level dynamics, increasing the likelihood of
shower activity and isolated thunderstorm development across the
forecast area. Drier air will start to filter over the area
Wednesday night.

Moderate to locally high concentrations of Saharan Dust will
continue to filter over the islands through most of the weekend with
concentrations decreasing to low (with isolated patches of moderate
concentrations from time to time) late Sunday through Tuesday.
Current guidance suggests that moderate to high concentrations of
Saharan Dust will then return by Wednesday.

Throughout the majority of the forecast period, warm to hot
conditions will persist, bringing a limited to elevated risk of heat
to coastal, urban and lower elevations. To mitigate the danger of
heat-related illnesses, both visitors and residents are advised to
keep following heat safety guidelines.

&&

.AVIATION...
(18Z TAFS)
Issued at 300 PM AST Wed Jul 22 2026

VFR conds across most TAF sites. However, TJSJ and TJPS will briefly
experience MVFR conditions with the heaviest RA and TS activity.
Winds will remain from the E-SE around 10 to 15 kts with higher
gusts, decreasing after 22/23Z. VCSH possible across most sites. HZ
will affect the islands from 23/12Z, lowering visibility to around
8SM to 6SM.

&&

.MARINE...
Issued at 300 PM AST Wed Jul 22 2026

The induced surface trough will continue to depart west of the
region this evening, maintaining scattered showers and
thunderstorms over portions of the local waters. Meanwhile, a
strengthening Atlantic surface high will maintain east-
southeasterly winds through Thursday before veering to the east-
northeast late Friday into the weekend as a weak tropical wave
approaches the region. This wave will increase the potential for
showers and thunderstorms, with locally higher winds and seas in
and near stronger convection. Beginning late tonight and
continuing into early Thursday morning, a drier air mass
accompanied by moderate Saharan dust concentrations will
overspread the region, resulting in hazy skies, reduced
visibility, and deteriorating air quality.

&&

.BEACH FORECAST...
Issued at 300 PM AST Wed Jul 22 2026

A low risk of rip currents will continue across the local beaches
tonight. Although the overall risk is low, life- threatening rip
currents can still occur, especially near groins, jetties, reefs,
and piers. Beachgoers are encouraged to exercise caution and swim
near a lifeguard whenever possible.

The risk of rip currents will increase to moderate on Thursday
and persist into the weekend for beaches along the north and east
coasts of Puerto Rico, including Vieques and Culebra, as well as
the U.S. Virgin Islands. Under a moderate risk, life-threatening
rip currents are possible, and beachgoers should exercise caution
before entering the water.

Lingering showers and isolated thunderstorms may continue over
portions of the local waters and nearby coastal areas through this
evening. Any thunderstorm that develops could produce frequent
lightning and brief gusty winds. A drier air mass and moderate
Saharan dust concentrations will overspread the region late
tonight into Thursday, leading to hazy skies and reduced
visibility.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

MORNING SHIFT...CAM/MMC
EVENING SHIFT....YZR/ICP