304
FXCA62 TJSJ 242100
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
500 PM AST Tue Sep 24 2024

.SYNOPSIS...

Winds will increase a little tomorrow with another round of
afternoon showers and isolated thunderstorms, but they should be
less widespread compared to the last few days. By Friday, a
tropical wave will move through--mostly south of the area. Warm to
hot conditions will continue through the weekend followed by
somewhat drier conditions in the first few days of next week.

&&

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

During the morning hours, surface weather observations and
satellite imagery recorded fair weather conditions across the
islands, accompanied by light winds with local variations. Once
again, one of the main concerns has been the heat, with heat index
values generally above 100 degrees F in the coastal and lower-
elevation areas of Puerto Rico and the U.S. Virgin Islands.
Maximum values reached as high as 116 and 122 degrees F in Vega
Baja and St. Croix, respectively.

Around noon, satellite imagery indicated the development of cloud
cover over the Cordillera Central, leading to the formation of
showers and thunderstorms throughout the interior of Puerto Rico.
According to radar estimates, about 1.5 to 2.5 inches of rainfall
have fallen, resulting in a few Flood Advisories across the
interior, Cabo Rojo, and Carolina. Additionally, two Special
Weather Statements have been issued due to strong thunderstorms.
While rain is expected to subside, isolated showers across the
waters and local passages in the U.S. Virgin Islands and eastern
sectors of Puerto Rico are expected later tonight and during the
overnight period.

The short-term forecast remains on track. According to the latest model
guidance, the upper-level trough across the western Atlantic will
gradually move away from us, and heights will start to increase
tomorrow. At the surface, winds will shift from the east and
increase somewhat in magnitude. Precipitable water values are
expected to fluctuate between 1.7 and 2.0 inches today, which is
considered normal for this time of year. Combining these
variables, we should see afternoon showers and isolated
thunderstorms again tomorrow, but they should be less widespread
compared to the last few days. The focus should be more on the
western-central and western sectors of Puerto Rico.

Warm to hot conditions are anticipated to continue over the next
few days, maintaining an elevated to significant heat risk
throughout the short-term period. Guidance indicates temperatures
at 925 mb in the above-normal range. Residents and visitors are
encouraged to 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...Friday through Tuesday....
.PREV DISCUSSION... /issued 518 AM AST Tue Sep 24 2024/

A band of moisture will move through early Friday morning
followed by a tropical wave--most of which will pass south of the
forecast area Friday night. Nevertheless some increase in rainfall
is expected, despite the fact that 500 mb temperatures will be
warmer than those of today and Wednesday. Precipitable water will
be found mostly between 1.95 and 2.05 inches even though the good
moisture is mostly supplied by the lower layers. While strong low
pressure systems will be found to the distant northwest, north
northeast and east, the flow across the local area on Thursday
will be easterly at 12 to 18 knots. The tropical wave will pass
through on Friday with oscillations in the flow over the weekend.
Finally on Monday and Tuesday flow at the surface becomes light
southerly. High pressure will again nose in from the east
northeast and conditions will dry out a little. Most days during
the long term period will still see afternoon convection over the
western and interior portions of Puerto Rico. On Monday and
Tuesday the showers and thunderstorms could also draw near to the
Greater San Juan and Bayamon Metropolitan areas.

At mid levels high pressure dominates the synoptic pattern while
in upper levels high pressure will remain to the northwest
although still quite influential in maintaining the dryness of the
mid to upper layers.

&&

.AVIATION...
(18Z TAFs)

SHRA/TSRA will develop along the Cordillera Central, spreading over
the coastal sections of PR thru 25/01z. Therefore, we expect mtn
obsc and MVFR conds over the interior through this evening. TSRA
will impact JSJ/JPS/JBQ between 24/18-22z, creating MVFR or even IFR
conditions. Elsewhere, expect VCTS. SHRA/TSRA could develop downwind
from the USVI into the surrounding waters, without impacting
terminals. Expect light SSE winds with sea breeze variations around
10 knots. Winds will become calm to light and variable aft 24/23z.

&&

.MARINE...

A weak high pressure ridging in over the region from the east northeast
will maintain light and variable winds through tonight. Winds will
become easterly and gentle to moderate thereafter. Showers and
isolated to scattered thunderstorms will develop from time to time
across the regional waters, and some will move into the coastal
waters of Puerto Rico each afternoon and evening. A northerly swell
will increase seas to around 4 to 5 feet on Wednesday night onwards.
Thunderstorms will become more isolated from tomorrow night through
Thursday, but the activity will increase by Friday as a tropical
wave is forecast to approach the regional waters.

&&

.BEACH FORECAST...

We will see one more day where all beaches will have a low risk
of rip currents and then the north, west and east beaches of
Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands will
begin to have a moderate and possibly high risk of rip currents by
the end of the week. Conditions improve again Monday night and
Tuesday of next week. For more details about the forecast, please
refer to the Surf Zone Forecast for Puerto Rico and the U.S.
Virgin Islands (SRFSJU).

&&

.SJU WATCHES/WARNINGS/ADVISORIES...

PR...None.

VI...None.

AM...None.

&&

$$

SHORT TERM...YZR/MNG
LONG TERM....WS
AVIATION...CAM/CVB
PUBLIC...ERG/MNG