322
FXCA62 TJSJ 130925
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Thu Jun 13 2024

.SYNOPSIS...

Moisture from a past tropical wave and frontal remnants will
reach sectors of north and east areas during the morning. Diurnal
heating and available moisture will promote localized and short-
lived showers and isolated thunderstorms in the afternoon for
western Puerto Rico. Although the heating trend will decrease
through Friday, Excessive Heat Warnings are still in effect today
from 10 AM to 6 PM for most urban and low elevation areas of the
metro area, north- central, northwestern, and western Puerto Rico.
Heat Advisories are also in effect at those same times for the
rest of the coastal areas of Puerto Rico, including Vieques and
Culebra, and St. Croix. Southeasterly winds and saharan dust will
promote a hot and hazy weekend.

&&

.SHORT TERM...Today through Saturday...

An upper level trough now extending across the northern Leeward
Islands into the eastern Caribbean will drift eastwards today
through Friday, while a mid to upper ridge is forecast to build
and then linger across the region into the upcoming weekend.
Surface high pressure extending southwards to just north of the
region and an induced trough east of the Lesser Antilles will
maintain a light to moderate east to northeast wind flow through
Friday.

Trailing low level moisture from a departed tropical wave and an
old frontal boundary will continue to be steered across the local
waters and reach portions of the north and east coastal area
during the rest of the morning. This will result in potential for
brief showers and possibly isolated thunderstorms with moderate to
locally heavy rains in isolated areas. Thereafter, a mix of good
sunshine and few clouds can be expected the rest of the day.
However the intense heating throughout the day along with
available pockets of moisture moisture will aid in the development
of some showers and isolated thunderstorms later in the
afternoon. This activity should be of short duration and prolonged
periods of heavy rainfall is not anticipated.

By late Friday and into the upcoming weekend, another surge of
Saharan dust of moderare to high concentration is forecast to
spread across the region while the local low level wind flow
becomes more southeasterly with and even drier airmass expected
through Saturday. By then with the southeasterly winds expect
another round of hotter and hazy conditions due to the combination
of suspended dust particulates and the mid to upper leve ridging,
which will favor subsidence and compression of the warm air
resulting in limited convective development across the islands.
Daytime high temperatures will be in the low 90s especially along
the north ans west coastal areas with maximum heat indices
expected to be in the low 100s once again with excessive heat
impacts probable particularly along the coastal and urban areas.

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

Hot and hazy conditions will continue to start the long term
period. Current model guidance suggests precipitable water (PWAT)
at below normal to normal values to start the period, with only
few patches of more humid air, from frontal remnants, moving
through the islands. Southeasterly surface windflow is expected to
persist on Sunday as a Surface high is present over the Atlantic.
This will steer warmer tropical air towards the islands,
promoting overall warm to hot conditions. Heat related products
will likely be issued for the islands later on. 925 mb
temperatures are forecast to be above normal to start the period.
Model guidance suggests more easterly winds to start the workweek
as the Atlantic surface high weakens. Saharan dust particles will
continue to start the period as well, promoting hazy skies at
least through Tuesday. Although model guidance suggest some
moisture over the mid levels, a more notable increase is suggested
by Wednesday. Most available moisture for the period will remain
below 850 mb, however. A decrease in PWAT values is now forecast
for Monday and most of Tuesday, with an increase by Tuesday night
and Wednesday. High pressure aloft will start to weaken as we head
into the workweek.

&&

.AVIATION...

(06Z TAFS)

VFR at all TAF sites durg prd but VCSH at TJSJ and USVI terminals
til 13/13Z. Mstly isold passing SHRA ovr regional waters en route
btw islands. Aftn VCSH/Isold TsrA psbl ovr ctrl interior and west PR
til 13/23Z...some may briefly impact areas in and around TJMZ/TJBQ.
SFC wnd fm E-NE 10-15 knots with local sea breezes accompanied by
higher gusts. Wnds bcmg less than 10 kts aft 13/23Z. Otherwise no
significant operational wx impacts.

&&

.MARINE...

Surface high pressure over the Atlantic and an induced trough east of
the area will promote light to moderate east to northeast winds
through tomorrow. Frontal remnants from the northeast and an upper
level trough are expected to increase the potential for showers and
isolated thunderstorms through tomorrow. Winds will continue to
diminish and veer, becoming east-southeast to southeast throughout
the weekend.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents today for easternmost St.
Croix. For tonight, there is a moderate risk of rip currents for
SE Puerto Rico. Low risk elsewhere today and tonight.

For tomorrow, a low risk of rip currents is forecast for all
beaches. Even with a low rip current risk, life-threatening rip
currents often occur in the vicinity of groins, jetties, reefs,
and piers.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning from 10 AM this morning to 6 PM AST this
     evening for PRZ001-005-008-010.

     Heat Advisory from 10 AM this morning to 6 PM AST this evening
     for PRZ002-003-007-011>013.

VI...Heat Advisory from 10 AM this morning to 6 PM AST this evening
     for VIZ002.

AM...None.
&&

$$

SHORT TERM...RAM
LONG TERM....MRR