487
FXCA62 TJSJ 112057
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
457 PM AST Thu Jul 11 2024

.SYNOPSIS...

Another pulse of suspended Saharan dust particulates will reach
the region on Friday and will remain through Sunday. An elevated
heat risk will also likely persist. Moisture from another tropical
wave is forecast to reach the islands by Friday night leading to
an increase in showers and thunderstorms throughout the weekend.
On Monday, another TUTT will approach the region enhancing
instability.

&&

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

Today, the islands were under the influence of partly cloudy skies,
showers, and warm temperatures. In the morning, showers developed
across the eastern half of Puerto Rico, while by the afternoon,
rainfall and thunderstorm activity developed along the interior
and western sections of Puerto Rico, where accumulations ranged
around 2 inches. The issuance of a flood advisory due to the
heaviest rainfall activity across municipalities like Aguada,
Anasco, and Rincon and a special weather statement due to the
strong thunderstorm activity, particularly along the western
sections of Puerto Rico, was necessary to keep the public informed
and safe. The maximum temperatures along the coast ranged from
the mid-90s to the upper 80s, and even across the higher
elevations, they were in the low 80s to upper 70s, which overall
hot weather conditions were experienced.

On Friday, another pulse of suspended Saharan dust particulates will
reach the islands, promoting hazy skies throughout the day.
However, the leading edge of a tropical wave will arrive,
increasing moisture content to above-normal levels, particularly
during the afternoon hours. We anticipate an increase in isolated
to scattered showers and some isolated thunderstorms in localized
areas, mostly across interior and western Puerto Rico.

By the beginning of the weekend, we foresee the arrival of a wind
surge along with trailing moisture associated with the past
tropical wave, which could bring squally weather for a very short
period. Nonetheless, by the afternoon hours of Saturday, we
anticipate an increase in thunderstorm activity with the potential
for frequent lightning and gusty wind conditions as another broad
area of suspended Saharan dust particulates will reach Puerto
Rico and the U.S. Virgin Islands. Expect hazy skies by late
Saturday evening.

&&

.LONG TERM...Sunday through Wednesday...
//from preview discussion//

Based on the latest models, during the beginning of the long-term
period, we will continue to have the presence of Saharan dust
across the region exacerbating health conditions for immunocompromised
individuals, vulnerable populations, and those sensitive to air
quality issues. During Sunday afternoon and evening, the Saharan
dust should be receding. Residual moisture from a tropical wave
will keep precipitable water mainly above normal values, with a
slight decrease to normal on Sunday. On Monday, PWAT should
increase again as a Tropical Upper- Tropospheric Trough (TUTT)
will approach the region and for now looks like it could be the
more active day of this forecast period. This feature will also be
evident in the mid and low levels of the atmosphere, with winds
first from the northeast on Monday, and then shifting from the
southeast on Tuesday and Wednesday. Early next week, enough
instability will be available to generate active afternoons across
the interior and western Puerto Rico. Temperatures in the 500 MB
are expected to drop to around -7 degrees Fahrenheit on Sunday and
Monday and that could be beneficial for thunderstorm development.
Trade winds will carry some showers across portions of Puerto
Rico and the Virgin Islands too, but the higher risk of flooding
and mudslides will be for the interior and west of Puerto Rico.
Potential impacts range from ponding water on roads to flooding in
poorly drained areas and urban and small stream flooding.

In terms of temperatures, warmer-than-usual conditions are
expected for most of the period. On Monday, if the rain
materializes, the temperature should stay a few degrees lower.
Generally, daytime highs will range from the lower 90s in lower
elevations to around 80 degrees in higher elevations. With
abundant moisture in the air, heat indices in coastal and urban
areas may soar above 108 degrees Fahrenheit.

&&

.AVIATION...

(18Z TAFS)


VFR conds prevail will prevail, but SHRA/TSRA will also dvlp btwn
11/16-21Z ovr wrn and interior PR with MVFR/IFR conds and mtn
obscurations at times. Any wx at active TAF sites will be brief or
at best VCNTY. E-ESE flow will cont with wind speed of 10-15 kt
inland and 15-20 kt with gusts to 26 kts along the coasts. Sct SHRA
ern PR thru byd 12/14Z where brief MVFR psbl. Aft 11/22Z land breeze
influences of less than 10 kt. Sea breezes in east flow will redevelop
aft 12/14Z.

&&

.MARINE...

A surface high pressure across the Atlantic Ocean will promote
moderate to fresh easterly to east southeasterly winds for the next
several days. Moisture from another tropical wave is expected to
reach the northeastern Caribbean by Friday leading to an increase in
showers and thunderstorms throughout the weekend, along with a drier
airmass.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents for beaches across Puerto
Rico and the U.S. Virgin Island and will remain like that through
the upcoming weekend. For additional information, consult the
Surf Zone Forecast (SRFSJU) issued by the NWS San Juan Office.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001-003-005-
     007-008-010-011.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ002.

AM...None.
&&

$$

SHORT TERM...MMC/GRS/CAM
LONG TERM....YZR
AVIATION...WS
PUBLIC DESK...GRS