404
FXCA62 TJSJ 240918
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
518 AM AST Tue Sep 24 2024

.SYNOPSIS...Warm-to-hot conditions will continue today. Winds will
increase a little Wednesday through Friday when a tropical wave
will move through--mostly south of the area. Warm and moist
conditions will continue through the weekend followed by somewhat
drier conditions in the first few days of next week.

&&

.SHORT TERM...Today through Thursday...

Tonight, mostly fair weather conditions prevailed inland across
Puerto Rico and the U.S. Virgin Islands. However, some lightning
activity lit the sky, particularly along the northern, western, and
southern coastal areas of Puerto Rico and the U.S. Virgin Islands,
as some showers and isolated to scattered thunderstorms developed
over the Atlantic and Caribbean waters and the waters between the
U.S. Virgin Islands and the Mona Passage. The overnight temperatures
remained in the lower 70s in the higher terrain and in the upper
70s to lower 80s in the urban/coastal areas. Like previous days,
the winds were relatively light and variable across the islands.

The short-term forecast remains unchanged. According to the latest
model guidance, the upper-level trough will continue to move from
the western Atlantic and will position to the north of our forecast
area, enhancing the upward vertical motion and better moisture
content today. Therefore, showers and thunderstorms will increase in
coverage once again, particularly this afternoon. Weak steering
winds will also lead to higher rainfall accumulations over the same
areas, increasing the potential for flooding and mudslides in steep
terrain, mainly along the Cordillera Central. On Wednesday, winds
are expected to become slightly stronger, around 10 to 15 knots, as
the deep-level trough will be out of the area by then. As
mentioned in previous discussions, the U.S. Virgin Islands should
experience a similar weather pattern over the next few days, with
little to no rain. However, showers and thunderstorm development
are forecast over the waters near the USVI.

Temperatures will be in the upper 70s to lower 80s over the
higher terrain, and upper 80s to lower 90s will persist across the
lower elevations of the islands during the morning and early
afternoon hours. Therefore, excessive heat conditions can be
anticipated throughout the short-term period. Advisories and
warnings for heat have been issued again today.

&&

.LONG TERM...Friday through Tuesday...

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...
(06Z TAFs)

Mostly VFR conditions at all TAF sites. Clds and SHRA are
expected to dvlp across the interior sections of PR aft 24/17Z,
followed by SHRA/TSRA with mtn obscurations and MVFR conds over
the interior through 24/22Z. TJSJ and TJBQ will experience brief
MVFR conds, particularly after 18Z. Winds less than 11 kt with a
few higher gusts along the coasts and near TSRA till 24/22Z.
TSRA will still be found offshore aft 24/22Z.

&&

.MARINE...A slight north to northeast swell will move into the
area on Wednesday and strengthen on Friday. Winds will increase
Wednesday through Friday, but gradually subside again on Monday
and Tuesday. Small craft advisories are not expected during the
next 7 to 10 days, but small craft will need to exercise caution
in some areas. Conditions will improve Monday and Tuesday of next
week.

&&

.BEACH FORECAST...We will see one more day where all beaches will
have a low risk of rip currents and then north and northeast
facing beaches will begin to have a moderate risk of rip currents.
Conditions improve again Monday night and Tuesday of next week.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 11 AM this morning to 5 PM AST this afternoon
     for PRZ001>003-013.

     Excessive Heat Warning from 11 AM this morning to 5 PM AST this
     afternoon for PRZ005-007-008-010-011.

VI...Excessive Heat Warning from 11 AM this morning to 5 PM AST this
     afternoon for VIZ002.

AM...None.

&&

$$

SHORT TERM/AVIATION...MMC
LONG TERM/MARINE....WS