Special Weather Statement, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
408 PM AST Mon Mar 22 2021

.SYNOPSIS...

Instability and moisture will increase during the day tomorrow;
showers are expected, especially in western and interior Puerto
Rico. Isolated thunderstorms are also expected. For the second half
of the week, less active conditions are expected, though showers, in
a typical pattern, are still likely.

&&

.SHORT TERM...Tonight through Wednesday...

A typical pattern of showers is expected overnight tonight into
tomorrow morning. Moisture remains generally constrained to the
lower levels, as the mid- to upper-level ridge remains dominant,
providing stability to the area. Tomorrow, however, a change in the
pattern is anticipated. A short-wave mid- to upper-level trough will
approach the region from the west through the day tomorrow,
traversing the region late tomorrow night into Wednesday. Because of
this, stability aloft is forecast to decrease. Meanwhile, a surface
perturbation will pull moisture across the region, though
precipitable water values are forecast to remain generally within
normal levels for March, around 1.2 to 1.5 inches. As such, the
vertical extent of moisture will increase, spreading into the mid-
levels. The 500 hPa temperature will decrease with the increase in
instability, with the GFS showing values of around -10C to -9C
during the afternoon and evening tomorrow. The combination of these
factors will support increased convective activity, especially in
western and interior Puerto Rico, as the winds will be generally out
of the east. Scattered to numerous showers are expected, with
isolated thunderstorms. Streamers are also possible during the
afternoon in eastern Puerto Rico. The increase in showers,
especially with the potential for locally heavy rainfall with
stronger storms and thunderstorms, will cause an increased potential
for urban and small stream flooding.

With the passage of the upper-level trough on Wednesday, stability
aloft will increase somewhat. Moisture will remain at near-normal
levels, though the vertical extent will decrease. As such, a
decrease in shower activity is expected by Wednesday morning, and
convection will also be inhibited compared to Tuesday.

.LONG TERM...Thursday through Monday...

Generally seasonal weather is expected for the long-term period,
with patches of moisture moving in from the east. Thursday looks
fairly dry and uneventful. A high pressure ridge aloft will exist
to our west, with troughing to our east. The atmosphere will
generally be dry, and under the influence of the ridging, with
below average precipitable water expected. High pressure at the
surface to our north will encourage breezy winds and lead to
fairly quick moving isolated showers, and these showers will
likely be unimpactful. Conditions will be more conducive for
showers on Friday. A weak patch of moisture is expected to arrive
during the day on Friday which will encourage shower development.
Furthermore, these showers may be enhanced by a trough of low
pressure aloft that will dig down over our region. One limiting
factor to the showers that will develop is that winds will remain
breezy at low-levels, leading to fast moving and less impactful
showers. However, any persistent showers over a given area may
lead to ponding of water over roadways and low-lying areas.

The weekend looks mostly dry. The aforementioned trough pushes
further south and east and a ridge will once again influence our
region with drier and more stable conditions. A few patches of
moisture will pass through during this period and into Monday as
well, but their impact is forecast to be minimal. Winds will
increase from Friday and into the weekend, and this will keep
showers moving quickly, and also may negatively impact marine
conditions.

&&

.AVIATION...

VFR conditions will prevail today. Cloudiness and showers are
developing across the interior and W-PR and will reduce VIS and
produce BKN ceiling at FL025-FL040 over JBQ btwn 22/18-20z. Winds
will continue from the E at 10-15 kt with higher gusts and sea
breeze fluctuations, becoming calm to light and VRB aft 22/23z.
Winds will return from E-ESE at 15 kt or greater mainly associated
to sea breeze variations after 23/13z. TSRA may develop tomorrow
across the Cordillera Central and west/PR during the afternoon.

&&

.MARINE...

The swell is subsiding, and conditions are no longer hazardous. Seas
of up to 6 feet are still expected, however, for much of the local
Atlantic waters and passages into tonight. Seas will continue to
subside through tomorrow, becoming relatively tranquil, up to around
5 feet by midweek.

For the beachgoers, there remains a high risk of rip currents at
northern beaches of Puerto Rico, as well as Rincon and Aguada,
Culebra, and northwestern St. Thomas. For beaches of Vieques, most
of the rest of the USVI, as well as portions of western and eastern
Puerto Rico, there is a moderate risk of rip currents.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  73  86  73  85 /  20  40  40  40
STT  73  84  72  83 /  20  30  50  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Tuesday afternoon for North
     Central-Northeast-Northwest-San Juan and Vicinity-Southeast.

     High Rip Current Risk through late tonight for Culebra-Mayaguez
     and Vicinity.

VI...High Rip Current Risk through late tonight for St.Thomas...St.
     John...and Adjacent Islands.

AM...None.
&&

SHORT TERM...RAM
LONG TERM....CRS
PUBLIC DESK...LIS

Perspectivas sobre Condiciones Peligrosas del Tiempo
Servicio Nacional de Meteorologia en San Juan PR
519 AM AST domingo 21 de marzo de 2021

AMZ710>745-PRZ001>013-230915-
San Juan y Vecindad-Noreste-Sureste-Este Interior-Norte Central-
Interior Central-Ponce y Vecindad-Noroeste-Oeste Interior-
Mayaguez y Vecindad-Suroeste-Culebra-Vieques-Las aguas costeras
cercanas y lejanas a la costa del Atlantico y Caribe-
501 AM AST lunes 22 de marzo de 2021

Esta perspectiva sobre las condiciones peligrosas del tiempo es para
Puerto Rico y las aguas costeras del Atlantico.

.Dia Uno...Hoy y esta noche

.Inundaciones...Aguaceros en la tarde pudieran resultar en acumulacion
de agua sobre carreteras y en areas de pobre drenaje.

.Viento...Se esperan vientos en exceso de 20 mph (17 nudos) a traves
de sectores de las aguas mar afuera y aguas costeras de las islas.

.Olas...Se espera oleaje picado de hasta 7 pies a traves de las aguas
mar afuera del Atlantico.

.Corrientes Marinas...Existe un riesgo alto de corrientes marinas
para las playas del norte de Puerto Rico y Culebra.

.Dias dos hasta el siete...lunes a sabado

El riesgo de corrientes marinas se mantendra alto para el norte de
Puerto Rico hasta el martes. Existe la probabilidad de tronadas el
martes sobre sectores del interior, norte y oeste de Puerto Rico, lo
cual pudiera resultar en inundaciones urbanas y de riachuelos. Se
pronostica que el viento y oleaje aumenten durante el fin de semana.

.Comunicado sobre informacion reportada por observadores...

No se espera activacion amplia de observadores. Favor de reportar
cualquier informacion sobre vientos, oleaje y corrientes marinas al
Servicio Nacional de Meteorologia en San Juan mientras siguen las
indicaciones de las autoridades locales y estatales.

AMZ715-725-VIZ001-002-230915-
San Tomas, San John e Islas Adyacentes-
Santa Cruz-Aguas cercanas del Atlantico y aguas
costeras adyacentes del Caribe-
501 AM AST lunes 22 de marzo de 2021

Esta perspectiva sobre las condiciones peligrosas del tiempo es para
Islas Virgenes Estadounidenses y las aguas costeras adyacentes.

.Dia Uno...Hoy y esta noche

.Viento...Se esperan vientos en exceso de 20 mph (17 nudos) a traves
de sectores de las aguas mar afuera y aguas costeras de las islas.

.Olas...Se espera oleaje picado de hasta 7 pies a traves de las aguas
mar afuera del Atlantico.

.Corrientes Marinas...Existe un riesgo alto de corrientes marinas
para las playas del norte de San Tomas.

.Dias dos hasta el siete...lunes a sabado

Un riesgo moderado de corrientes marinas prevalecera a traves de las playas
del norte de San Tomas, y a traves de las playas del norte y este de Santa
Cruz hasta el fin de semana. Se pronostica que el viento y oleaje aumenten
durante el fin de semana.

.Comunicado sobre informacion reportada por observadores...

No se espera activacion amplia de observadores. Sin embargo, favor
de reportar cualquier informacion sobre vientos, oleaje y corrientes
marinas al Servicio Nacional de Meteorologia en San Juan mientras
siguen las indicaciones de las autoridades locales y estatales.