National Weather Service Today's Weather Impact Levels

198
FXCA62 TJSJ 202122 RRA
AFDSJU

Area Forecast Discussion...DELAYED
National Weather Service San Juan PR
522 PM AST Wed Nov 20 2024

.SYNOPSIS...

Stable weather conditions will persist for the next few days.
However, weather conditions will deteriorate this weekend as a
polar trough and a surge of tropical moisture settles over the
northeastern Caribbean. Hazardous marine conditions will persist
tonight and return during the weekend.

&&

.SHORT TERM...Today through Friday...

Mostly sunny to partly cloudy skies prevailed across the islands
today. Scattered showers were noted mainly across the northeastern
sections of Puerto Rico throughout the day. The Doppler radar
estimated around three tenths of an inch over Fajardo. High
temperatures were in the mid to upper 80s across most urban areas of
the lower elevations, and once again in the low 90s in Ponce and
Guanica. A high of 88F was reported at the St. Thomas and St. Croix
airports. The wind prevailed from the northeast between 8 and 12 mph
with higher gusts and sea breeze variations along the southern coast
of PR. The highest wind gust reported today was 26 mph at the King
Airport in St. Thomas.

A polar trough will exit the eastern coast of the U.S. by Friday,
while a weak surface high pressure north of the area moves further
eastward into the central Atlantic. This will cause winds to
gradually veer and become more easterly by late tonight,
southeasterly by Thursday afternoon, and then southerly by Friday. A
surface front will also move across the western Atlantic and a pre-
frontal trough is expected to develop over the northeastern
Caribbean, increasing moisture across the local area by the end of
the workweek and into the weekend. Therefore, shower activity will
increase in general over the USVI by Thursday and across the islands
on Friday. A shift in steering winds from the east to southeast will
favor shower development in the afternoon hours over portions of the
interior and north/northwest Puerto Rico.

High temperatures will be in the the mid to upper 80s across most
coastal areas of the islands, except in southern PR where it can
reach the low 90s once again on Thursday and Friday, while the
minimum temperatures could drop into the low 60s across the higher
elevations and mountain valleys.


&&


.LONG TERM...Saturday through Wednesday...

.PREV DISCUSSION... /issued 540 AM AST Wed Nov 20 2024/

High pressure at upper levels dominates the long period despite
the passage of an upper level trough saturday evening well to the
north of the area. The associated southwesterly jet stream will
likely never get past Cuba. At mid levels high pressure becomes
entrenched about 1000 miles east northeast of San Juan, Puerto
Rico and moves very little. As the flow around this high is from
the south modest moisture will be brought up out of the Caribbean
during the period. Peak moisture will be seen late Sunday night
and Monday morning. At the surface high pressure northeast of the
area--much where the mid level high is also--keeps flow southerly.
A weak wave passing to the west over the Caribbean begins to
amplify south of Jamaica and flow turns southeasterly for the
remainder of the period. While this does bring in some moisture,
flow is never particularly moist at any one level but precipitable
water values remain above two inches except for a 24 hour period
from early Tuesday to early Wednesday when air from the mid
Atlantic is brought back in around the high pressure east
northeast of the area. While the low pressure expected to form
over the Central Caribbean will not directly affect Puerto Rico
or the U.S. Virgin Islands, periods of showers will keep the area
wet. At this time this does not appear to generate expectations
for anything more than ponding of roads and some stream rises.

&&

.AVIATION...
(18Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, diurnally induced SHRA may cause
periods of -RA/VCSH in and around the USVI/PR terminals btw 21/16z-
22z. NE winds up to 10 knots blo FL040 will continue to prevail
across most terminals with land/sea breeze variations.

&&

.MARINE...

Gentle to moderate northerly winds will prevail through late tonight,
when easterly winds return. Pulses of the northerly swell will
continue to arrive tonight, but conditions are likely to remain
below small craft advisory criteria. Another small long-period
northerly swell is expected for the weekend.

&&

.BEACH FORECAST...

Buoy 41043, about 170 NM NE of San Juan indicated a 7 ft swell at
11-13 seconds and should persist through late tonight. The local
San Juan now indicates seas at 6 ft at 12-14 seconds. Therefore,
a High Surf Advisory was added to the northern coastal area of
Puerto Rico while the High Rip Current Risk was extended through
at least 6 PM Thursday. Please refer to CFWSJU.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Thursday afternoon for PRZ001-002-
     005-008-010-012.

     High Surf Advisory until 6 PM AST Thursday for PRZ001-002-005-
     008.

VI...High Rip Current Risk through Thursday afternoon for VIZ001.

AM...None.
&&

$$

SHORT TERM...DSR/CVB
MARINE/BEACH...CVB
LONG TERM...PREV
AVIATION..ICP/DSR

NWS SJU Office Area Forecast Discussion