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