666
FXCA62 TJSJ 212112
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
512 PM AST Thu Nov 21 2024

.SYNOPSIS...

Tonight, we expect the development of some showers over eastern
Puerto Rico. A gradual increase in moisture will be experience
from Friday onwards enhancing showers and thunderstorms over the
area. A northwesterly swell will increase the rip current risk on
Sunday. Except for a dry slot that crosses Monday night conditions
will remain mostly wet after this Friday.

&&

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

Sunny to partly cloudy skies prevailed across Puerto Rico and the
U.S. Virgin Islands today. Localized showers persisted over Fajardo
and nearby waters throughout the day, and the Doppler radar
estimated close to 1 inch of rain with this activity. Maximum
temperatures were between 83 and 86 degrees along the northern
sections of the islands, and between 86 and 91 along the southern
coastal areas. Light winds prevailed from the east to southeast.

A weak surface high north of the region will strengthen over the
central Atlantic during the next few days. This will promote
southeasterly winds across the local area through at least Saturday.
At upper levels, a polar trough will exit the eastern coast of the
U.S. by Friday and it is expected to remain west of the area through
the period. Meanwhile, the ridge across the Tropical Atlantic will
continue to strengthen at lower and mid-levels, promoting better
moisture transport from the southeastern Caribbean into the local
area. The precipitable water content is expected to increase between
1.75 and 2.00 inches on Friday and Saturday. Although the upper
level trough is expected to remain mainly west of the region, the
500 mb temperatures are expected to decrease from -4C today to -6C
by Friday afternoon. This pattern should favor the development of
afternoon showers with isolated thunderstorms in diurnal activity
over portions of the interior and along the north-northwestern
sections of PR.

Higher moisture content and warmer temperatures due to the
southeasterly component of the winds will increase the threat for
excessive heat across most lower elevations of the islands.

&&

.LONG TERM...Sunday through Thursday...
//from previous discussion//

At upper levels, the sub-tropical jet between Florida and Haiti
will join the polar jet well north of the local area, but will be
unable to come much closer to the area due to high pressure that
stretches from the Central Caribbean to the tropical Atlantic
along 20 north which will drift a little south during the period.
A decaying wave will approach the area and cross the Windward
Islands from the east early Sunday morning to bring additional
moisture to the area. This moisture will move quickly past the
forecast area to the south and feed the developing north-south
trough north of Panama while pulling in drier air in from the
east over us on Monday. As the trough develops a low over
Jamaica, winds will become more southerly and bring more moisture
from the southeast Caribbean for continued shower activity.

500 mb temperatures will be mostly minus 5 to minus 6 during the
period, so there will present a chance of thunderstorms--mainly
during the afternoons over Puerto Rico and over the local waters
at night. Although some local urban and small stream flooding
could develop, showers should move just fast enough to prevent
major river rises during the period. Nevertheless most areas will
have at least some rain each day.

&&

.AVIATION...
(18Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, afternoon SHRA and possible iso
TSTMs can develop over the NW quadrant of PR btw 22/16z-22z. ESE
winds up to 10 knots with land/sea breeze variations should prevail
through the fcst period.

&&

.MARINE...

Light to gentle east to southeasterly winds will prevail through
late Saturday. 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...

Conditions have improved considerably since yesterday. The high
rip current risk along the northern coast will become moderate
tonight. But the increasing swell from the north northwest on
Sunday will elevate the rip current risk to high through at least
Monday.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for PRZ001-002-
     005-008-012.

VI...None.
AM...None.
&&

$$

SHORT TERM...ICP/DS
LONG TERM...WS
AVIATION...DS
MARINE/BEACH FORECAST...MMC