435
FXCA62 TJSJ 192002
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
402 PM AST Sun May 19 2024

.SYNOPSIS...

Hazy skies and warmer-than-normal conditions will persist through
early next week, with limited afternoon shower and isolated
thunderstorm development across western portions of Puerto Rico
and downwind of the local islands. A wet and unstable weather
pattern continues to be expected by midweek of next week as a
deep- layered trough approaches from the west and combines with
tropical moisture. Tranquil marine conditions and a low rip
current risk will prevail throughout the next few days.


&&

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

Stable weather conditions prevailed across the region during the
early morning hours. As the day progressed, shower activity
developed in the northeastern and interior sections, resulting in XX
rain in XX, as indicated by Doppler Radar. Daytime temperatures
ranged from the upper 80s to lower 90s across the coastal areas,
with heat indices of 105 to 110 in the northern coastal regions.

A variable weather pattern is expected as afternoon convection
diminishes for the rest of the day. In the early evening hours,
there is potential for shower activity across the coastal waters,
streaming from the island`s southeastern coast. By Monday,
instability will slightly decrease as the upper-level trough
dominating the area moves eastward. Although instability will remain
with favorable conditions in the zonal flow, the islands can expect
a convective pattern driven by local effects.

Upper-level conditions will rapidly deteriorate again by Tuesday as
a deep upper trough sinking just over Cuba leaves the positive
vorticity advection side over the region, facilitating cloud
formation and shower activity. Although instability will be present
for widespread shower activity, it will be localized in the
afternoon hours across the interior and northwestern quadrant due to
the southeasterly wind flow resulting from the broad surface high
pressure over the central Atlantic.

.LONG TERM...Wednesday through Sunday...

From previous discussion issued at 414 AM AST Sun May 19 2024

A wet, unstable weather pattern is expected through the second half
of the week as a deep layered trough moves through the Caribbean
basin to then form a surface low in the western Atlantic by the
weekend. The surface induced trough that is projected to form
south of Hispanola on Wednesday night will cause an acceleration
of the surface winds along with a rapid increase of moisture
sourced from the ITCZ as the airmass moves northward in the
eastern Caribbean. Winds will continue to veer towards a southerly
direction by the end of the week as the low strengthens to the
northwest of the area. Throughout this time the proximity of the
low`s mid to upper-level jet will maintain strong winds aloft
which will increase the chance of thunderstorm activity as
ventilation is enhanced. Conditions seem to calm through the
weekend as this system moves further from the local area, however
light surface wind flow and abundant moisture will allow diurnal
heating and local effects to bring heavy rainfall during the
afternoon hours.

Due to all of this, Wednesday through the weekend will consist of
periods of heavy rainfall for mostly all of Puerto Rico and the
USVI. Flash flooding due to continuous rainfall is possible through
this event also strong thunderstorms are also likely to occur. Stay
tuned for further updates as we approach these days.


&&

.AVIATION...
(18Z TAFS)

Brief MVFR conditions are possible due to SHRA and VCTS near TJBQ
& TJSJ until 19/21Z. They will improve by resulting in VFR
conditions for all the TAF sites. Winds will remain from the E-SE
with sea breeze variations and diminishing, becoming VRB, and
increasing again by 20/14Z. Tomorrow, another round of showers
will result in VCSH and VCTS across northern TAF sites.


&&

.MARINE...
A surface high pressure across the central and northeast Atlantic
will result in moderate easterly winds through the rest of the weekend.
Tranquil marine conditions will therefore prevail throughout the
forecast period. Afternoon showers and isolated thunderstorms could
move from western Puerto Rico into the coastal waters each day.


&&

.BEACH FORECAST...

There is a low rip current risk for across all area beaches of
Puerto Rico and the U.S. Virgin Islands. However, life-
threatening rip currents can often occur in the vicinity of
groins, jetties and piers. The risk will likely become moderate
for southwestern Puerto Rico and St Croix starting Monday night.
In addition, with possible maximum heat indices between 102-107
degrees or higher, along the local beaches, heat exhaustion will
be likely with prolonged exposure. Stay hydrated!


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001-002-005-
     008-010-011.

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

AM...None.
&&

$$

SHORT TERM...ICP/LIS
AVIATION...LIS
PUBLIC...MMC/MRR