031
FXCA62 TJSJ 232109
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
509 PM AST Mon Sep 23 2024

.SYNOPSIS...

Light winds will prevail over the next few days with showers and
thunderstorms each day, but generally less on Wednesday. A low
risk of rip currents will be seen tonight and Tuesday due to
light winds. Winds will increase somewhat on Wednesday through
Friday when a mild tropical wave is expected to move across the
forecast area.

&&

.SHORT TERM...Tonight through Wednesday...

Calm conditions in terms of rainfall prevailed in the morning
across the islands, accompanied by light winds with a southerly
component. The primary concern has been the heat, with heat index
values generally ranging from 108 to approximately 115 degrees F
across the coastal and lower-elevation areas of Puerto Rico and
the U.S. Virgin Islands, validating the Heat Advisory and
Excessive Heat Warning. Maximum values reached as high as 120 and
123 degrees F in Vega Baja and St. Croix, respectively.

After midday, satellite imagery indicated the development of cloud
cover across the Cordillera Central, leading to the formation of
showers and thunderstorms throughout the interior of Puerto Rico.
According to radar estimates, around 1 to 1.5 inches of rainfall
have fallen. At the moment, two Special Weather Statements have
been issued due to strong thunderstorms. At least for the next
hour, shower activity due to diurnal heating is expected to
continue mainly across western sectors of Puerto Rico.

For tonight, expect rain activity to subside in coverage, but
some isolated showers across the waters and local passages, U.S.
Virgin Islands, and eastern sectors of Puerto Rico cannot be ruled
out of the forecast.

During the remainder of the short term-period, a similar pattern
with showers and thunderstorms can be expected, particularly
across the interior each day. This pattern will be influenced by
diurnal heating, local effects, and the presence of an upper-level
trough moving from the western Atlantic. At the surface, light ESE
winds will continue to lead higher rainfall accumulations over the
same areas, increasing the potential for flooding and mudslides
in areas of steep terrain. On Wednesday, winds will turn more form
the east and increase a little, helping to move showers faster.

In addition, an elevated to significant heat risk will persist
throughout the short-term period. Residents and visitors should
monitor the forecast and take precautions to stay hydrated by
drinking plenty of water, wearing light and breathable clothing,
and avoiding prolonged sun exposure, especially during peak heat
hours.

&&

.LONG TERM...Thursday through Monday...
.PREV DISCUSSION... /issued 529 AM AST Mon Sep 23 2024/

High pressure in the lower levels will be found just north of the
area and this will induce a more typical easterly surface flow.
That high pressure will move westward and a mild tropical wave
will move through the U.S. Virgin Islands, Puerto Rico and most
of the eastern Caribbean south of the area Friday afternoon and
Friday night. On Saturday a shearline will approach the islands
from the north but remain north of 20 north. This will maintain
easterly flow and given that the moisture does not really diminish
we will continue to see typical shower and thunderstorm formation
Saturday and Sunday. On Monday flow becomes southerly and very
light and temperatures will begin to climb a few degrees. This
will lead to stronger showers and thunderstorms in central and
western Puerto Rico.

At upper levels a weak TUTT low will be found just south of Puerto
Rico on Thursday. When it moves west, a second TUTT will dive in
from the northeast and will create a environment only somewhat
favorable to active convection given that 500 mb temperatures will
rise during the period--especially after the tropical wave
passes. Strong high pressure at upper levels will hold over Cuba
and then move over southern Florida adding to the stability over
the weekend and into Monday. With light southerly surface winds
beginning then, we will see a warming trend.

&&

.AVIATION...
(18Z TAFs)

SHRA/TSRA will develop along the Cordillera Central, spreading over
the W, N and E coastal municipalities of PR thru 24/01z. Therefore,
we expect mtn obsc and MVFR conds over the interior through this
evening. TSRA will impact JSJ between 23/18-20z, creating MVFR or
even IFR conditions. Elsewhere, expect VCTS. SHRA/TSRA could develop
downwind from the USVI into the surrounding waters. Expect southerly
winds with sea breeze variations around 10 knots. Winds will become
calm to light and variable aft 23/23z.

&&

.MARINE...

A weak high pressure ridging in over the region from the east
northeast will maintain light and variable winds through tomorrow.
Then, winds will become gentle to moderate and with an easterly
component. Showers and isolated thunderstorms will develop from time
to time across the regional waters, and some will move into the
coastal waters of Puerto Rico each afternoon. A northeasterly swell
will increase seas to around 4 to 5 feet during the latter part of
the week.

&&

.BEACH FORECAST...

The Rip Current Risk will remain low tonight and Tuesday, then the
risk will increase across the north and northeast beaches of
Puerto Rico, Culebra, and the U.S. Virgin Islands around Wednesday
through Friday. Rip current risk could be high on Friday due to a
4 to 5 foot swell reaching the area from the northeast.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.

VI...None.

AM...None.
&&

$$

SHORT TERM...RAM/YZR/MNG
LONG TERM...WS
AVIATION...CAM/RAM
PUBLIC...ICP/MNG