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000
FXCA62 TJSJ 142106
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
506 PM AST Sun Apr 14 2024

.SYNOPSIS...

An unstable and wet pattern will lead to limited to moderate
excessive rainfall hazard levels or flooding impacts in the coming
days. Additionally, hazardous marine and life-threatening surf zone
conditions will persist.

&&

.SHORT TERM...Tonight through Tuesday...

Showers affected windward coastal areas during the early morning
hours before dissipating for the remainder of the morning. These
showers left less than a tenth of an inch across northeastern
portions of Puerto Rico, Culebra, and the northern USVI.

By noon, the leading edge of a surface-induced perturbation was
approaching the CWA from the east. By early afternoon, gradually
increasing cloud coverage and shower activity began to affect the
USVI, northeastern, interior, and western/southwestern Puerto Rico.
The latest imagery from the Polar Blended-Percent of Normal Total
Precipitable Water (TPW) indicates between 150%-165% above normal
TPW spread between PR and the northeastern Leeward Islands.
Therefore, higher moisture will continue to stream across the area
this evening and tomorrow. Despite the higher moisture content and
low-level instability brought by the surface perturbation,
convective activity has remained shallow for the most part. The
Doppler radar estimated up to 0.50 inches of rain across northern
and northeastern Puerto Rico, mostly over the Luquillo mountain
range, and up to 1.5 inches of rain between Yauco and Maricao.
Expect this activity to continue this evening and late tonight.

For Monday and Tuesday, weather conditions will become even more
unstable as an upper-level trough approaches from the
northwest,combining with high low-level moisture, causing the
mid-level ridge to erode and promoting cold air advection over
the local islands. The 500 mb temperatures will drop to -9.0
degrees Celsius by midweek, promoting steep temperature lapse
rates across the region. The GFS Galvez-Davison Index suggests the
potential for isolated to scattered thunderstorms with the
possibility of heavy rainfall. The ECMWF Precipitation Extreme
Forecast Index (EFI) suggests high confidence among its ensemble
members in predicting above-normal precipitation for this time of
year through midweek.

Despite the area with higher moisture convergence being expected
north of Puerto Rico, wet and unstable weather conditions will
combine with diurnal heating and local effects, further increasing
the potential for downpours throughout the remainder of the short-
term forecast. Very localized convergence zones capable of producing
prolonged heavy showers cannot be ruled out, posing particular risks
for urban and flood-prone areas. Quick river rises, flash flooding,
and landslides are likely in the coming days.

.LONG TERM...Wednesday through Sunday...

.PREV DISCUSSION... /issued 505 AM AST Sun Apr 14 2024/

Wednesday through at least early Thursday morning, inclement
weather and a moist and unstable environment will persist due to
the lingering mid to upper trough crossing into the northeastern
Caribbean. This will provide good ventilation aloft along with the
advective low level moisture pooling for a continued showery pattern
and isolated thunderstorm development. The low level moisture convergence
caused by the east southeast winds and local and diurnal effects will
favor good potential for thunderstorm development and flooding rains
at least until late Wednesday or early Thursday. Thereafter, recent
model guidance continued to initialize well and still suggest moisture
erosion with increasing stable conditions aloft by Thursday afternoon.
A gradual drying trend is expected from then onwards, as a mid to upper-
level ridge will build northwards from the western Caribbean, and a
surface high pressure ridge builds across the west Atlantic. This in
will bring a return of east-northeast winds once again through Friday,
followed by winds becoming more easterly and increasing over the
following weekend. This expected pattern will also lead to an overall
drier airmass at least Thursday through Friday, followed by the return
of occasional passing trade wind showers and more typical isolated
to scattered afternoon showers in and around the islands over the
weekend.

&&

.AVIATION...
(18z)

SHRA are expected to increase through the forecast period. Periods
of reduced VIS and low ceilings are possible with the activity,
especially for USVI terminals and TJSJ. After 22z, TSRA expected to
develop in the local waters, mostly around the USVI. Mountain
obscuration expected after 13-14Z for the Cordillera Central. VCTS
also expected after 15/17Z for TJBQ. Winds will be from the ESE at
14-19 kts, with stronger gusts.


&&

.MARINE...

A surface ridge over the north-central Atlantic and broad surface
trough across the eastern Caribbean will generate moderate to locally
fresh east- northeasterly winds. A fading northerly swell and the
choppy wind driven seas will continue to promote confused seas
tonight and tomorrow. An approaching upper level trough and induced
surface trough will continue to promote inclement weather across the
local waters tonight and into midweek of this week.


&&

.BEACH FORECAST...

Atlantic Nearshore buoys continue to indicate breaking waves above 6
feet. Additionally, pulses of a weak northeasterly swell will
continue to affect the northern regional waters through the
workweek. Consequently, the Rip Current Statement will remain in
effect for all beaches along the northern coastline of Puerto Rico
and Culebra. For more information and details please refer to the
latest Surf Zone Forecast (SRFSJU), and the Coastal Hazard Message
product (CFWSJU).


&&

.HYDROLOGY...

.PREV DISCUSSION... /issued 1009 AM AST Sun Apr 14 2024/

A wet pattern is expected to begin today and stretch into the
middle of the week. An area of enhanced moisture (surface trough)
will combine with an upper level trough, resulting in unsettled
weather conditions. The risk of urban and small stream flooding,
water surges, mudslides and isolated flash flooding will increase.
The areas most affected are expected to be eastern and northern
half of Puerto Rico, as well as the interior. The Virgin Islands
and southern Puerto Rico will receive pulses of showers and
thunderstorms as well. Conditions are expected to improve by
Thursday. A Hydrologic Outlook (ESFSJU) will be issue later today.

&&

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

VI...None.
AM...Small Craft Advisory until 6 PM AST Tuesday for AMZ711.

     Small Craft Advisory until 6 PM AST Monday for AMZ723.

&&

$$

SHORT TERM/MARINE/BEACH FORECAST...CVB
PUBLIC...YZR
AVIATION...ERG/CAM