530
FXCA62 TJSJ 242049
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
449 PM AST Mon Jun 24 2024

.SYNOPSIS...

A dense plume of Saharan dust is expected to arrive on Tuesday
morning along with a very 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...Tonight through Wednesday...

Bands of showers and thunderstorms associated to a passing tropical
wave affected Puerto Rico and the USVI during the day. The strongest
activity was observed during the afternoon hours across the
northwestern municipalities of Puerto Rico, and the San Juan metro
area. Doppler radar estimated between 1.0 to 2.5 inches of rain
across the mentioned sectors. It was very hot today too, with
maximum temperatures reaching the lower 90s across the lower
elevations. Heat indices were seen between 105 to 110 degrees
Fahrenheit along the coastal and urban areas.

The tropical wave is forecast to exit the local area by this
evening. Then, a drier airmass with a dense Saharan Air Layer will
arrive and persist through at least Thursday. Moderate to severe
concentrations of Saharan Dust will result in hazy skies and
lower visibilities across Puerto Rico and the USVI.

Hot temperatures are anticipated for Tuesday through Wednesday.
Maximum temperatures could reach the mid 90s across the coastal and
urban sectors. Excessive Heat Warning and Heat Advisories are
anticipated. A Heat Watch will be in effect starting on TUesday
morning for Puerto Rico and the USVI. Afternoon convection will
remain possible for northwestern Puerto Rico, but conditions
aloft and the presence of Saharan Dust will not favor widespread
rainfall activity.

.LONG TERM...Thursday through Monday...

./FROM PREV DISCUSSION...Issued at 439 AM AST Mon Jun 24 2024/

Through early in the weekend, there will be a mid-to upper-level
ridge across the northeastern Caribbean. Its still possible that
afternoon showers will form across the western sections of Puerto
Rico. Instability will slightly increase from late Thursday and
Friday as an induced low-level trade wind perturbation streams
across the local area raising moisture content that will increase
the chance of isolated thunderstorms and showers.

A trade wind pattern due to an established surface high across the
Atlantic basin will drag tropical moisture into the islands through
the weekend into next week. According to global model guidance, PWAT
values will fluctuate from 1.70 to 2.10 inches, just above seasonal
climatological values for the region. That moisture, along with
diurnal heating, will promote the development of afternoon showers
and isolated thunderstorms each day across the western interior
sections of Puerto Rico. The arrival of drier air on Monday may
reduce the chance of showers, however do still expect a typical
seasonal pattern of passing showers and afternoon convection for the
start of the following week.

&&

.AVIATION...

(18Z TAFs)

SHRA/TSRA from a tropical wave will continue to move across the area
through the early evening hours, reaching the terminals at times.
Brief period of MVFR conds are possible with this activity. Low-
level winds will prevail from the east to southeast at 12-18 kts
through the period, with higher gusts on Tuesday. HZ due to Saharan
dust with possible reduced VSBY across the area terminals is
expected as early as Tuesday morning.

&&

.MARINE...

A surface high pressure over the central Atlantic will promote
light to moderate southeasterly winds. Trade wind showers will move
across the regional waters from time to time. Increasing winds and
showers with thunderstorms are expected through tonight across the
local waters. Hazy skies are expected from Tuesday through Thursday
due to Saharan dust.

&&

BEACH FORECAST...

There is a low to moderate risk of rip currents across PR and the
U.S. Virgin Islands.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Watch from Tuesday morning through Tuesday
     afternoon for PRZ001>003-005-007-008-010-011.

VI...Excessive Heat Watch from Tuesday morning through Tuesday
     afternoon for VIZ001-002.

AM...None.

&&

$$

SHORT TERM...LIS
LONG TERM....GRS
AVIATION...DSR