173
FXCA62 TJSJ 260804
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
404 AM AST Wed Jun 26 2024

.SYNOPSIS...

The dense plume of Saharan Dust will continue to affect the local
islands through Thursday. This plume will continue to promote
hazy skies, lower visibilities and hot temperatures across the
area. Expect warmer than normal temperatures each day, resulting
in excessive heat warnings and heat advisories across Puerto Rico
and the USVI.

&&

.SHORT TERM...Today through Friday...

Saharan dust and warmer than normal temperatures are expected to
continue through at least Thursday across the U.S. Virgin Islands
and Puerto Rico. An Excessive Heat Warning and a Heat Advisory are
in effect for all coastal counties, please refer to the latest heat
product NPWSJU for more information. Heat indices higher than 112
degrees Fahrenheit are expected. Hazy skies will continue today as
the area remains under the influence of a strong Saharan Air Layer
with moderate to high concentrations of Saharan dust. This drier air
mass will limit shower activity in general, but diurnally induced
streamers developing off the USVI and smaller islands are possible,
in addition to isolated thunderstorms developing this afternoon over
west/northwest PR.

On Thursday and Friday, a gradual increase in moisture content is
expected as an induced perturbation on the trade winds moves from
the east. A 700-500MB ridge north of the region will promote
northeasterly steering winds, while mainly easterly trades prevail
at the surface due to the Azores High. This will cause showers and
thunderstorms to develop over the interior and south/southwestern
quadrant of Puerto Rico, while an advective pattern with passing
showers persists across the USVI and the east/northeast sections of
PR.

&&

.LONG TERM...Saturday through Wednesday...

The latest precipitable water guidance suggests values ranging
around normal climatological levels across Puerto Rico and the U.S.
Virgin Islands during the weekend. Nonetheless, as a surface
high-pressure system positions across the Atlantic basin, we
anticipate the introduction of tropical moisture into the islands
through at least the upcoming workweek. This weather pattern will
allow moisture to filter over the islands from time to time, and
this, combined with the diurnal heating, will promote the
development of afternoon showers and isolated thunderstorms,
particularly across the western interior sections of Puerto Rico,
as mostly easterly winds will dominate the forecast area. As
mentioned in previous discussions, the tourists and citizens of
Puerto Rico and the U.S. Virgin Islands will experience a slight
change in weather conditions as drier air will filter across the
region on Monday, reducing the chance of showers through Tuesday.
Nevertheless, a typical seasonal weather pattern of passing
showers and afternoon convection is expected.

On Wednesday, expect a gradual increase in shower and possible
thunderstorm activity across the forecast area, particularly over
the Caribbean waters, as a tropical wave now being monitored by
the National Hurricane Center moves south of us. However, we
encourage people to stay updated with any changes in the forecast.

&&

.AVIATION...

(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. HZ due to Saharan dust could drop VSBY
around 6 miles. SHRA/TSRA is expected to develop btw 26/18z-22z in
and around TJBQ, causing tempo MVFR conds. ESE winds expected at 12-
16 kt with stronger gusts and sea breeze variations aft 26/14z.

&&

.MARINE...

A surface high pressure over the central Atlantic will promote light
to moderate east-southeasterly winds. Trade wind showers will move
across the regional waters from time to time due to a tropical wave
moving south over the Caribbean Waters. Hazy skies are expected
through Thursday due to Saharan dust.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents across southern PR and
St. Croix. A low risk is forecast elsewhere.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning from 10 AM this morning to 6 PM AST this
     evening for PRZ001-003-005-007-008-010>012.

     Heat Advisory from 10 AM this morning to 6 PM AST this evening
     for PRZ002-013.

VI...Excessive Heat Warning from 10 AM this morning to 6 PM AST this
     evening for VIZ002.

     Heat Advisory from 10 AM this morning to 6 PM AST this evening
     for VIZ001.

AM...None.
&&

$$

SHORT TERM/AVIATION...DS
LONG TERM/MARINE/BEACH FORECAST...MMC