338
FXCA62 TJSJ 252023
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
423 PM AST Tue Jun 25 2024

.SYNOPSIS...

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

&&

.SHORT TERM...Tonight through Thursday...

The presence of the Saharan Air Layer promoted hazy skies across the
region today. Fair weather conditions were observed across the
islands, with very limited precipitation across the western
municipalities of Puerto Rico. It was very hot today too, with
temperatures in the upper 80s to mid 90s in the lower and higher
elevations. The Luis Munoz Marin International Airport reported a
maximum temperature of 92 degrees Fahrenheit. The previous record
was 97 degrees Fahrenheit in 1983. Today, heat indices reached
the 110 to 115 degrees Fahrenheit in many places, especially
along the northwestern and north central portions of Puerto Rico.
An Excessive Heat Warning and a Heat Advisory was in effect for
all the islands through the late afternoon hours.

Warmer-than-normal temperatures will continue through at least
Thursday due to the presence of Saharan Dust and high low-level
humidity. At this time showers are not anticipated, however, if
showers get to develop they will be short lived over western and
northwestern Puerto Rico. Similar weather conditions are expected
through Thursday afternoon. An Excessive Heat Watch will be in
effect each day. By Thursday, a trade wind perturbation will
increase humidity, and the potential for showers and isolated
thunderstorms across western Puerto Rico.


.LONG TERM...Friday through Tuesday...

./FROM PREV DISCUSSION...Issued at 526 AM AST Tue Jun 25 2024/

The inherited forecast remains unchanged. The latest model
guidance continues to suggest a slight increase in instability
through the end of the workweek into the early weekend as an induced
low-level trade wind perturbation streams across the local area.
This perturbation will allow the moisture content to increase
through the mid-levels of the atmosphere, increasing the chance of
isolated thunderstorms and showers. Precipitable water models
show values ranging from normal to slightly above normal
climatological levels. By the weekend, the surface high-pressure
system will position across the Atlantic basin, dragging tropical
moisture into the islands through next week. At this time, we
anticipate that this moisture, along with the diurnal heating,
will promote the development of afternoon showers and isolated
thunderstorms each day, particularly across the western interior
sections of Puerto Rico, as mostly easterly winds will dominate
the forecast area.

A slight change in weather conditions is foreseen as drier air will
filter across Puerto Rico and the U.S. Virgin Islands on Monday,
which may reduce the chance of showers. Nevertheless, a typical
seasonal weather pattern of passing showers and afternoon
convection is expected.

&&

.AVIATION...

(18Z TAFs)

A dense plume of Saharan dust will promote hazy skies across TAF
sites, that will result in lower VIS. The winds will remain mainly
from the east to east-southeast at 10-20 kt with gusts between 20
and 30 kt for the rest of the afternoon hours. Some isolated showers
are possible across the interior and western PR between 25/18-23z.
Winds should become lighter during the evening and overnight hours,
then increase again around 26/13-15Z from the east to east-
southeast.

&&

.MARINE...

A surface high pressure over the central Atlantic will promote
moderate to fresh east-southeasterly winds. Trade wind showers will
move across the regional waters from time to time. Hazy skies are
expected through Thursday due to Saharan dust.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning until 6 PM AST this evening for PRZ001-
     003-005-007>012.

     Excessive Heat Watch from Wednesday morning through Wednesday
     afternoon for PRZ001-003-005-007-008-010>012.

     Heat Advisory until 6 PM AST this evening for PRZ002-004-006-013.

VI...Excessive Heat Warning until 6 PM AST this evening for VIZ001-
     002.

     Excessive Heat Watch from Wednesday morning through Wednesday
     afternoon for VIZ002.

AM...None.
&&

$$

SHORT TERM...LIS
LONG TERM....GRS
AVIATION...YZR
PUBLIC DESK...RVT