118
FXCA62 TJSJ 300823
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
423 AM AST Tue Apr 30 2024

.SYNOPSIS...

A broad surface high pressure over the western Atlantic will
weaken in the next few days. Expect breezy northeasterly winds
through at least midweek. From mid-week onwards, instability and
moisture levels increase once again as a mid to upper level trough
lingers over the western Atlantic and lighter east to southeast
winds return. Coastal and marine conditions will remain hazardous
through at least late Wednesday.

&&

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

Breezy conditions and scattered to locally numerous showers
prevailed overnight as the remnants of an old front moved through
the region. Observed rainfall amounts were from half an inch in
Quebradillas to one inch in Naguabo and less than a quarter of an
inch across the U.S. Virgin Islands. Minimum temperatures were from
the mid-to-upper 70s across coastal areas to the mid-60s across the
higher elevations. Wind gusts were just over 30 mph across the
northeast coast of PR and in St. Thomas.

A broad surface high pressure over the western Atlantic will weaken
during the next few days as it moves slowly into the Central
Atlantic. The last couple of soundings indicated the presence of
drier air above 700 mb. However, the remnants of the front have kept
a moist layer at the lower levels. Similar conditions to previous
days are expected, with breezy winds, cloudiness, and passing
showers across the islands throughout the day. Also, afternoon
showers with possible isolated thunderstorms could develop over
portions of the interior and southwestern PR.

A wetter and unstable pattern is still expected to evolve on
Wednesday and Thursday as an upper-level trough approaches the area
from the west, and an induced surface trough develops north of the
region. In response, moisture pooling and lighter winds can be
expected, further enhancing shower and thunderstorm development
across the local area. The main impacts are urban and small stream
flooding, localized flash flooding, and mudslides in areas of steep
terrain. Steering winds are expected to shift further from the S/SW
on Thursday, increasing the potential for showers across San Juan
and its vicinity.

High temperatures will remain in the mid-to-upper 80s along the
coastal and urban areas and from the mid-to-upper 70s along the
mountains and valleys. Minimum temperatures will range from the mid
and upper 70s across coastal areas to the mid-60s in the higher
elevations.

&&

.LONG TERM...Friday through Monday...

The latest model guidance continues to suggest wet and unstable weather
conditions even through the end of the workweek, notonly for the
island of Puerto Rico but also for the U.S. Virgin Islands. This
pattern should prevail as an upper-level trough approaches the
area from the west, and an induced surface trough develops north
of the region enhancing additional rainfall activity and allowing
it to be the dominant feature throughout the long-term period. On
Friday, a mid to upper level, yet maxima, should move across the
area with winds around 70 knots. This yet maxima will allow the
trough to deepen, enhancing the unstable conditions. By the
weekend, expect the Precipitable Water (PW) values to range above
normal climatological levels for this of the year to above two
standard deviations. We foresee active afternoons each day with
the potential increase in the frequency of showers and isolated
thunderstorms. As a side note, heat indices across the lower
elevations of the islands could likely range between 102 and 106
degrees on Friday and Saturday before the onset of afternoon
convection.

Overall, the main hazards from Friday into the beginning of the workweek
are the increased risk of flooding across the islands and the
risk of mudslides, particularly in areas of steep terrain in
Puerto Rico. Therefore, we encourage citizens and visitors to be
aware of any additional updates in the forecast.

&&

.AVIATION...
(06z) TAFS

Remnants of a weak front producing sct SHRA with max tops at FL120
will continue to cause -SHRA and brief MVFR cigs at
TJSJ/TIST/TISX/TJBQ at times. TSRA could develop near TJPS this
afternoon, but mostly VCTS expected thru 22z. ENE winds at 13-18 kt
with stronger gusts near 30 kt will continue through the period.

&&

.MARINE...

A sub tropical high pressure across the western Atlantic will
continue to promote moderate to fresh trade winds through at least
Wednesday night. As a result, expect hazardous seas for small craft
operators due to confused seas associated with the increasing winds
and a northeasterly swell spreading across the local waters.

&&

.BEACH FORECAST...

A northerly swell and stronger winds are resulting in High Risk
of Rip Currents across beaches from Mayaguez to Fajardo, Culebra,
and USVI through at least late Wednesday. For more information
and details about the latest forecast please refer to the Surf
Zone Forecast (SRFSJU) and the Coastal Hazard Message product
(CFWSJU).

&&

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

VI...High Rip Current Risk through late Wednesday night for VIZ001.

     High Rip Current Risk through this afternoon for VIZ002.

AM...Small Craft Advisory until midnight AST Wednesday night for
     AMZ711-712.

     Small Craft Advisory until 6 PM AST Wednesday for AMZ716.

     Small Craft Advisory until noon AST Wednesday for AMZ723-741-742.

     Small Craft Advisory until 6 PM AST this evening for AMZ726.

&&

$$

SHORT TERM...DS
LONG TERM/MARINE/BEACH FORECAST...MMC
AVIATION...DS
PUBLIC DESK...DS/MMC