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000
FXCA62 TJSJ 102014
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
414 PM AST Wed Apr 10 2024

SYNOPSIS...Improving weather conditions as drier air begins to
move in overnight. However, on Friday more showers are expected.
The presence of an upper-level trough and increased moisture
levels may lead to an increased flooding early next week.
Additionally, moderate to locally strong winds, coupled with
pulses from a long period northerly swell, will persist,
maintaining hazardous marine conditions. Consequently, dangerous
swimming and life-threatening beach conditions are anticipated
during the next few days.

&&

.SHORT TERM...Tonight through Friday...

A surface ridge strengthening across the western Atlantic will
maintain breezy trades through the rest of the week. Wind speeds are
forecast to sustain above 15 mph through the day across coastal
regions, bringing passing showers through the days and nights.
During this time, a mid to upper-level ridge across the upper
Antilles will maintain overall stable weather conditions, reducing
the chance of convective development. For tonight, rainfall is
expected across the eastern coastal areas as NE surface flow
continues. Minor ponding of water is possible across urban areas
with shower activity.

Throughout Thursday, a drier airmass begins to sink over the local
islands as the surface high north of the region migrates
northeast into the high latitudes of the Atlantic. Due to this
precipitable water values will begin to drop, however residual
moisture will still allow showers to develop. Best chance of rain
will be across eastern sections during the morning and there is a
chance of afternoon showers for the interior to southwestern
sections of PR.

As surface winds become more easterly through Thursday, they will
assist the movement of a moist airmass sourced from the remnants
of a frontal boundary across the eastern Caribbean Basin. This
moisture is expected to arrive through Friday morning,
significantly increasing the rate of showers throughout the day.
St. Croix appears to have a good chance for rainfall during this
time due to it`s proximity to the bulk of moisture. Afternoon
rainfall across the interior to western sections of Puerto Rico
will be enhanced as well. The upper to mid-level ridging will
still act to reduce the intensity of shower development, however
showers can be frequent at times especially with 15-20 mph
easterly trades.

&&

LONG TERM...Saturday through Wednesday...
/from previous discussion/

Recent model guidance continues to suggest a significant shift in
weather patterns during the long- term forecast period,
transitioning from dry and stable conditions to a wetter and
unstable setup. Precipitable water values are expected to
fluctuate, starting from below-normal thresholds below 1.3 inches
on Sunday and Monday, then rising to above-normal thresholds
exceeding 1.7 inches on Tuesday and Wednesday. This transition is
attributed to the retreat of the mid-level ridge and presence of a
drier-than-normal air mass during the weekend, followed by an
influx of tropical moisture and the proximity of an upper-level
trough early next week. The prevailing steering flow should remain
easterly, driven by a broad surface high pressure spreading
across the North Atlantic. However, as this feature weakens, wind
speeds are forecast to diminish from approximately 15-25 mph to
5-15 mph early next week.

While fair weather conditions are expected until early Monday, the
possibility of passing showers overnight and limited afternoon
convective activity exists each day. Conversely, an increase in
shower activity with potential isolated thunderstorm development
is expected from Monday night onward as conditions become
increasingly favorable for deep convective development, with 500
mbar temperatures dropping as low as -9 degrees on Wednesday. The
anticipated rains may lead to flooding impacts, although the
excessive rainfall risk level remains uncertain at this time.
However, if the trough`s influence becomes more direct, an
elevated flooding risk is likely and flooding impacts could occur
as early as Tuesday morning. Breezy conditions are anticipated
through the weekend, primarily affecting coastal areas, with limited
wind impacts expected. Temperature fluctuations should remain
within seasonal thresholds throughout the forecast period.

&&

.AVIATION...
(18Z TAFS)

Mainly VFR conditions are expected across all terminals, with
prevailing NE winds reaching speeds of up to 15-20 knots,
accompanied by higher gusts and sea breeze variations. SCT-SHRA may
cause VCSH during the afternoon, spreading to S/SW PR, may cause
MVFR at TJPS.

&&

.MARINE...

A surface ridge located in western Atlantic will generate fresh to
locally strong east-northeasterly winds through the rest of the
week, causing an increase of passing showers and brief gusty winds.
Northerly swell will continue spreading across the Atlantic waters
and passages through Thursday. The wind and swell interaction will
maintain confused, hazardous seas for small craft over the next few
days. For details, refer to the Marine Weather Statement
(MWWSJU).

&&

.BEACH FORECAST...

Increasing winds and a long-period northerly swell will likely
generate dangerous swimming and life-threatening rip current
condition, due to large breaking waves of up to 12 feet. Given
these conditions, a High Surf Advisory and High Rip Current Risk
are in effect for the north-facing beaches of Puerto Rico,
Culebra, and the northern US Virgin Islands, where localized
coastal flooding and beach/dune erosion is possible. Between
tonight and thursday, life-threatening rip current conditions will
spread to the beaches of Vieques and St Croix. For details, refer
to the Coastal Hazard Message (CFWSJU) and Surf Zone Forecast
(SRFSJU).

&&

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

     High Surf Advisory until 6 PM AST Thursday for PRZ001-002-005-
     008-010-012.

     High Rip Current Risk through late Thursday night for PRZ013.

VI...High Surf Advisory until 6 PM AST Thursday for VIZ001.

     High Rip Current Risk through Friday afternoon for VIZ001.

     High Rip Current Risk from Thursday morning through late Friday
     night for VIZ002.

AM...Small Craft Advisory until 6 AM AST Saturday for AMZ711-712-716-
     723-726-733-741.

     Small Craft Advisory until 6 AM AST Friday for AMZ742.

&&

$$

RAM/YZR/RC