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000
FXCA62 TJSJ 130858
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
458 AM AST Sat Apr 13 2024

.SYNOPSIS...
A strong surface ridge over the north-central Atlantic and a weak
surface trough associated with the remnants of a frontal boundary
across the Caribbean waters, will promote moderate to locally strong
east- northeasterly winds and passing showers across the region during
the rest of the early morning hours. A gradual break in cloud cover
and a decrease in the frequency of the passing showers is forecast later
this morning and during the rest of the day. Drier air filtering in
from the north and building high pressure ridge aloft will reduce the
frequency of the passing showers during the rest of the weekend. Breezy
conditions and occasional passing showers will however continue through
the weekend, with afternoon showers expected to develop over parts of
the central interior and west to southwest sections of Puerto Rico
and mainly on the west-end and downwind of the U.S. Virgin Islands.

&&

.SHORT TERM...Today through Monday...

Cloudy skies prevailed through the overnight hours across the
islands as the remnants of an old front crossed the region. The
Doppler radar noted persistent light to moderate showers with this
moisture band across Puerto Rico through the early morning hours.
The radar estimated between 1-2 inches of rain across eastern Puerto
Rico, and from a few hundredths to half an inch elsewhere across the
island. Across the USVI, rainfall totals were less than a tenth of
an inch. Minimum temperatures were from the mid-60s across the
higher elevations to the mid-70s across the lower elevations. Wind
gusts were between 16 and 22 mph across coastal areas.

For the rest of the weekend, the area will remain under the
influence of a mid-level ridge extending from the west. Although
drier air will gradually filter later today and through early
Sunday, patches of low-level moisture will move at times from the
Atlantic waters as east-to-northeast steering winds prevail through
the short-term period. Breezy conditions should continue today
across the region and return briefly by Monday morning across the
Caribbean waters and the USVI. The precipitable water content is
forecast to drop between 1.25 and 1.50 inches through Sunday
afternoon. Therefore, shower activity should develop mainly due to
diurnal and local effects and mainly across portions of
west/southwest PR each afternoon.

A more unstable and wetter pattern is expected to evolve on Monday
as a mid-to-upper-level trough moves from the northwest and a low-
level trough develops over the eastern Caribbean. These features
will cause the precipitable water content to increase again between
1.75-2.00 inches, promoting colder 500 mb temperatures of near -7
degrees Celsius. Therefore, shower and thunderstorm activity is
expected to increase across the local area. The threat for urban and
small stream flooding will remain elevated during the first part of
the workweek.

.LONG TERM...Tuesday through Saturday...
Tuesday through at least Wednesday a very moist and unstable
environment will persist due to the presence of the mid to upper
trough crossing into the northeastern Caribbean then lingering over
the area through midweek. This will provide good ventilation and
divergence aloft along with strong dynamics for thunderstorm development,
as the 500 mb advective temperatures are forecast to range between
minus 7 to minus 9 degrees Celsius. Meanwhile, increasing moisture
convergence and pooling is forecast due to an induced surface trough
and the dominant east southeast winds. As a result, the potential
for thunderstorm development and flooding rains will be high as this
wetter and unstable pattern will evolve and continue through at least
Wednesday. Based on most recent GFS model guidance which has been
initializing fairly well, there will be a gradual drying trend from
Thursday onwards as a mid to upper- level ridge builds from the
western Caribbean, and a surface high pressure ridge builds across
the west Atlantic. This will promote east to northeast winds once
again, with winds becoming more easterly by the following weekend.
This expected pattern will also lead to an overall drier airmass
across the region at least Thursday through Friday, followed by
the return of occasional passing trade wind showers and more
isolated to scatters afternoon showers in and around the islands
over the weekend.

&&

.AVIATION...

(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, brief MVFR areas should end around
13/10z at TJPS/TJBQ as the remnants of an old frontal boundary moves
westward across the Mona Passage. Winds will continue from the ENE
btw 12-18 kts with gusts at 20-30 kts. Sea breeze variations expected
aft 13/13z at TIST/TISX/TJPS.

&&

.MARINE...
A strong surface ridge over the north-central Atlantic and a weak
surface trough associated with the remnants of a frontal boundary
across the Caribbean waters will continue to generate fresh to
locally strong east- northeasterly winds and passing showers
across the regional waters. The arrival of drier air filtering in
from the north later today will reduce the frequency of the passing
showers during the rest of the weekend. However the breezy conditions
and occasional passing showers will continue. A fading northerly swell
today and choppy wind- driven seas will maintain hazardous conditions
to small craft. Therefore small craft advisories and precautionary
statement will continue for portions of the regional waters through
the weekend. Please refer to the latest Marine Weather Message (MWWSJU)
for detailed information. Seas are forecast to slightly improve late
Sunday into early next week.

&&

.BEACH FORECAST...
Dangerous swimming and life-threatening rip currents will continue
through at least later this afternoon across the east and north-
facing beaches of PR and the USVI, due to wind driven seas, rough
surf conditions with breaking waves around 6 feet and higher at
times. Given these conditions, a High Rip Current Risk remains in
effect for the northwest to northeast beaches of the islands.
Please refer to the latest Coastal Hazard Message (CFWSJU) and
Surf Zone Forecast (SRFSJU) for detailed information. Beach goers
should remain alert as a moderate risk of rip currents will
continue through the rest of the weekend across most east and
northern beaches of the islands.

&&

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

VI...High Rip Current Risk through this afternoon for VIZ002.

AM...Small Craft Advisory until 6 PM AST this evening for AMZ711-712-
     741.

     Small Craft Advisory until noon AST today for AMZ716-723-733.

     Small Craft Advisory until 6 AM AST early this morning for
     AMZ726-742.

&&

$$

SHORT TERM...DS
LONG TERM....RAM
AVIATION...DS