690
FXCA62 TJSJ 071111 CCA
AFDSJU

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
711 AM AST Thu Nov 7 2024

.SYNOPSIS...
Unsettled weather is expected to persist over the next few days,
bringing frequent showers and strong thunderstorms. With soils
already saturated and elevated streamflows, flooding impacts are
likely. Boating and swimming are strongly discouraged today due to
hazardous seas, large breaking waves, and life-threatening rip
currents, with these conditions expected to persist through Friday.
Stay safe and stay informed! For a depiction of the areas at risk,
visit the Experimental Graphical Hazard Weather Outlook:
https://www.weather.gov/erh/ghwo?wfo=sju.

&&

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

Overnight radar and satellite analysis indicate an active night. The
first pulse, characterized by persistent light to moderate showers
and a few thunderstorms, faded around midnight. Since then, showers
and thunderstorms have redeveloped across the region, triggered by a
low-level induced low pressure that developed overnight from a
deepening upper-level trough, as indicated by satellite imagery and
TJUA NEXRAD`s Velocity Azimuth Display (VAD) wind profile signature.
While surface observation reports recorded rainfall totals of up
to half an inch across northern and northeastern Puerto Rico since
8 PM AST, radar-estimated accumulations in Culebra and Saint
Thomas, USVI, reached around three-quarters of an inch. Overnight
temperatures ranged from the lower 60s in higher elevations to
around 80 degrees across coastal observing stations of southern
Puerto Rico and the U.S. Virgin Islands. Winds were generally
light and variable, with higher gusts near the thunderstorms.
counterpart

Unsettled weather is anticipated to continue through much of the
short-term forecast period. Although the low-level induced low will
shift away from the region, its driving feature, an upper-level low,
will position itself favorably to the southwest today. In
combination with the upper low, a trough of low pressure, currently
monitored by the National Hurricane Center for tropical cyclone
formation, will move across the area through Friday, supporting an
influx of tropical moisture and promoting unstable conditions.
Satellite-derived precipitable water values suggest above-normal
November levels, fluctuating between 2.1 and 2.4 inches.
Consequently, frequent and strong thunderstorms are anticipated over
the next 24-48 hours, with high rain chances (70-90%) across all
land areas.

As the steering flow shifts from northeast to south-southeast
following the passage of the surface trough, rainfall will gradually
focus from eastern Puerto Rico today to southern Puerto Rico tonight
and into Friday, with the U.S. Virgin Islands also experiencing high
rain chances throughout this period. A weaker steering flow is also
expected to increase the likelihood of higher rainfall accumulations
from slow-moving showers. Given these conditions, an elevated to
significant risk of excessive rainfall exists today and Friday,
raising concerns for urban and small stream flooding, flash
flooding, river flooding, and mudslides across the region.
Additional hazards include frequent lightning and gusty winds
generated by thunderstorms, as well as breezy to locally windy
conditions along coastal areas. Despite the increased chance of rain
and cloudiness, southerly winds on Friday may lead to warmer
temperatures.

According to current model guidance, Saturday`s weather pattern is
expected to be less stormy. East-southeasterly winds and daytime
heating will likely lead to more localized showers with isolated
thunderstorms, primarily in the afternoon. Flooding impacts are
likely to occur due to periods of moderate to locally heavy rainfall
over soils that are already saturated. Thunderstorm activity could
increase Saturday night as a tropical wave approaches the region.
For updates on excessive rainfall, lightning, and any other hazard
risk in the coming days, please visit the Experimental Graphical
Hazard Weather Outlook at https://www.weather.gov/erh/ghwo?wfo=sju.

.LONG TERM....Sunday through Thursday...

Some instability and a wet spell will prevail for the long-term
period across the region. By Sunday, tropical moisture from a
tropical wave now located several hundred miles east of the
Lesser Antilles will move south of the area. Although a
significant amount of moisture is associated with this tropical
wave, so far today, global model guidelines and The Glvez-Davison
Index (GDI) suggest a scenario where the bulk of the moisture
with showers and scattered thunderstorms will remain just south of
the islands only affecting mostly southeastern section of Puerto
Rico and the Caribbean waters due to a rapid change in the surface
winds from the northeast in response of a broad building high
pressure moving eastward into the central Atlantic replacing the
surface trough located north of the region generated by the
reflection of an upper level low at the southwestern Caribbean.
The east-northeast wind flow will drag a slight area of drier air,
limiting the showers on Sunday afternoons somewhat for a brief
period. East winds return quickly as the board surface ridge moves
more into the central Atlantic, inducing the islands again for
moisture values above the climatological normals.

From Monday to Wednesday, the main weather feature will be a mid
to upper-level ridge providing stable conditions for the vertical
profile, inhibiting most of the shower development. Surface winds
will persist mainly from the east with, veering winds by
Wednesday into Thursday due to a low pressure developed over the
western Atlantic moving eastward into the Central Atlantic. This
surface change will increase the relative humidity at 700-300 MB.
There, the islands can expect widespread showers and
thunderstorms for the last part of the upcoming workweek. There
are some discrepancies in the amount of moisture available from
the two global model guidance (ECMWF & GFS). However, both of them
show a wet pattern.

&&

.AVIATION...

(06Z TAFS) Increasing SHRA/TSRA across the region will likely result
in brief MVFR conditions, with BKN-OVC at FL015-025 and reduced
visibility. Light to calm and variable winds, becoming E-NE and
increasing to 10-15 knots between 07/14-22Z. Higher gusty winds are
expected near TSRA.

&&

.MARINE...

Recent data from the bouy network around the CWA shows seas
between 8 to 12 feet. A surface high pressure across the western
to central Atlantic and the proximity of a trough of low pressure
will promote fresh to locally northeasterly winds for today into
tonight. These wind-driven seas will combine with weak pulses of
long-period northeasterly swell in the area, resulting in
hazardous marine conditions. Small Craft Advisories are in effect
across most of the regional and local waters and passages through
at least Friday.

&&

.BEACH FORECAST...

Pulses of long-period wave energy arriving at the locally exposed
coastal areas and the high seas across the region will result in
large breaking waves up to 10 feet across all the northern coastal
areas of Puerto Rico, where a High Surf Advisory was issued this
morning until 6 PM this evening. For the western section of PR,
Culebra, Vieques, and the U.S. Virgin Islands, there is a high rip
current risk for the rest of the workweek in some of those points.
Please visit the Surf Zone Forecast (SRFSJU) for more related
information.

&&

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

     High Surf Advisory until 6 PM AST this evening for PRZ001-002-
     005-008.

     High Rip Current Risk through Friday afternoon for PRZ010.

     High Rip Current Risk through late tonight for PRZ013.

VI...High Rip Current Risk through late tonight for VIZ002.

     High Rip Current Risk through late tonight for VIZ001.

AM...Small Craft Advisory until 2 PM AST Friday for AMZ711-712-716-
     741.

     Small Craft Advisory until 6 AM AST Friday for AMZ723-742.

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

&&

$$

SHORT TERM & AVIATION...ICP
LONG TERM, MARINE & BEACH FORECAST....LIS