180
FXCA62 TJSJ 250926
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
526 AM AST Tue Jun 25 2024

.SYNOPSIS...

As mentioned in previous discussions, a dense plume of Saharan
dust is expected to arrive on today along with a dry airmass.
These conditions will promote hazy skies and hot temperatures from
Tuesday through Thursday. Significant rainfall activity is not
anticipated due to the presence of the dust particles.

&&

.SHORT TERM...Today through Thursday...

Calm weather conditions prevailed overnight, with warmer-than-normal
low temperatures across Puerto Rico and the U.S. Virgin Islands. In
the satellite imagery, a mid-to-upper-level cloud deck was observed
moving over the islands, limiting nighttime cooling overnight. The
winds were mainly from the east-southeast at 10 mph or less.
Additionally, the Saharan Air Layer began to produce hazy skies
across the region.

Due to the warmer-than-normal low temperatures, we can expect
maximum temperatures to rise to near or above-normal values today
and tomorrow. The arrival of a Saharan Air Layer will reduce the
available moisture, but the high low-level humidity will still lead
to warm and hot heat indices. This has prompted an Excessive Heat
Warning for most of the coastal areas and western interior urban
sections of Puerto Rico, Culebra, and all of the U.S. Virgin
Islands. The rest of mainland PR and Vieques are under a Heat
Advisory, indicating the potential hazards of these weather
conditions.

We cannot rule out some showers arriving while steering by the winds
across the windward sections, but it should be minimal today. During
the afternoon, some showers will develop across PR`s mountain and
western sections.

Due to similar weather conditions, an Excessive Heat Watch will be
in effect tomorrow. Additionally, the hazy skies will remain across
the islands throughout the short term. The heat spell may extend
through at least Thursday when a trade wind perturbation will
increase humidity, increasing the potential for showery weather and
some isolated afternoon strong convection.

&&

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

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...

(06Z TAFs)

Hazy skies will limit VIS btwn 4 and 6 SM or less. The winds will
remain mainly from the east to east-southeast at 10-20 kt with gusts
between 20 and 30 kt. Some showers will develop across the interior
and western PR between 25/18-23z.

&&

.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.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents across PR and the U.S.
Virgin Islands. A low risk is forecast for western PR.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning from 10 AM this morning to 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 from 10 AM this morning to 6 PM AST this evening
     for PRZ002-004-006-013.

VI...Excessive Heat Warning from 10 AM this morning to 6 PM AST this
     evening for VIZ001-002.

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

AM...None.
&&

$$

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