Areal Flood Advisory 9, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
955 AM AST Wed Mar 24 2021

.UPDATE...Forecast remains on track. Latest GOES-16 precipitable
water imagery shows a surge in moisture moving into the area
through the day. This moisture in combination with a trough axis
extending from the Leeward Islands westward into the Central
Caribbean along with local and diurnal effects will result in
enhanced shower and possibly isolated thunderstorm activity across
interior and western Puerto Rico this afternoon. In addition, with
the low-level flow being unidirectional from the east to east-
southeast, a streamer is likely to develop downwind from El Yunque
and affecting portions of the San Juan metro, resulting in
additional shower activity. Urban and small stream flooding will
be possible with the heaviest activity. Across the USVI, just
isolated showers are expected.

&&

.AVIATION...Mainly VFR conditions are expected. SHRA and iso TS
expected across interior and western PR between 24/17z and 24/23z.
Additional SHRA possible across the San Juan area. The activity
over PR will result in VCSH across all PR terminals. Passing SHRA
possible from time to time across the USVI and Leeward Island
terminals, resulting VCSH across the area terminals there. No
significant impacts to operations expected at this time. Low-
level winds will be from the E between 10 and 15 kts with sea
breeze variations through 24/22z, becoming light and variable
overnight.

&&

.MARINE...No changes to the previous marine discussion. Mainly
tranquil seas through Thursday, with choppier seas expected by
Friday and into the upcoming weekend as winds increase. A moderate
risk of rip currents is expected for all the north and some east-facing
beaches of the islands today.

&&

.PREV DISCUSSION... /issued 421 AM AST Wed Mar 24 2021/

SYNOPSIS...

Showers and possibly even a few weak thunderstorms are possible
later today due to above average moisture and favorable
atmospheric conditions. Calmer weather is expected for later in
the week due to the influence of an upper level ridging. Above
average moisture and scattered showers are in the forecast for
next week. Calmer seas will prevail with the return to wind-driven
hazardous seas for this weekend.

SHORT TERM...Today through Friday...

A weak trade wind cap will allow low-level moisture to increase
today. An area of precipitable water (PWAT) content of around 1.50
inches is currently moving across the Leeward Islands and will reach
the local area during the day. At upper levels, a ridge is building
west of the region, while the trough is moving further east and away
of the region. An induced low-to-mid level trough will promote an
east to northeast wind flow and an advective pattern, that will
favor night/early morning showers across the U.S. Virgin Islands and
portions of east/northeast Puerto Rico.

For today, due to the proximity of the upper level trough and surge
in low-level moisture, scattered to locally numerous showers with
isolated thunderstorms cannot be ruled out in diurnal convection
over portions of the interior and west/southwest PR. Urban and small
stream flooding is possible with this activity. At least through
Friday, PWAT content is forecast to continue between 1.20-1.40
inches, but at the same time, stability aloft should gradually
increase as the upper level ridge strengthens west and over the area.

LONG TERM...Saturday through Wednesday...

Long range models continue to suggest an upper-level trough to our
east for the weekend, with a mid to upper level ridge way off to the
west. The trough will bring in cooler air aloft and encourage upward
motion and the formation of more potent showers for Saturday and
possibly Sunday as well. However, a few factors will act to limit
the impact of these showers. Surface high pressure to our north will
keep east-northeasterly winds fairly breezy, thus the showers will
move quickly. Furthermore, there will not be much moisture to work
with, and mid-levels are forecasted to be particularly dry. Thus,
scattered showers will be possible for northeast Puerto Rico for
Saturday and Sunday morning, with afternoon showers and possibly
isolated thunderstorms for western and southwestern Puerto Rico.
These showers will likely move fast enough so that flooding will
not be an issue, but ponding of water over roadways is possible.

For the beginning of the workweek, we lose the forcing from the
upper level trough as it moves off to the east, but moisture
associated with the trough will decouple from the trough and move
westward into our region. Winds are expected to remain easterly
to east-northeasterly and quite brisk. So fast moving showers will
continue to impact eastern and northern Puerto Rico in the
morning hours. With afternoon moderate shower activity for western
and southwestern Puerto Rico. Winds in the long-term forecast
look brisk enough that the marine conditions will be negatively
impacted.

AVIATION...Mainly VFR conditions are expected to prevail across all
the terminals during the next 24 hours. However, SHRA is expected to
develop in and around TJSJ/TIST/TISX from 15z-21z, causing tempo
MVFR conds. Also, there is a chance for TSRA in and around TJPS fm
16z-22z. East to northeast winds btw 8-15 kt with sea breeze
variations expected after 14z.

MARINE...

Seas will be fairly tranquil for the next few days, with wave
heights generally below 5 feet, and regional buoys now reflect
these calmer seas. Seas will become choppy once again as winds
pick up on Friday and through the weekend. Small Craft Advisories
will likely be issued for wind-induced swell event. Isolated
showers will continue over the local waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  74  85  74 /  30  40  30  40
STT  84  73  85  73 /  50  30  30  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

SHORT TERM...GL
PUBLIC DESK...CAM/CVB

Perspectivas sobre Condiciones Peligrosas del Tiempo
Servicio Nacional de Meteorologia en San Juan PR
409 AM AST miercoles 24 de marzo de 2021

AMZ710>745-PRZ001>013-250815-
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-
409 AM AST miercoles 24 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

.Tronadas...Existe una probabilidad de tronadas con fuertes lluvias
y rafagas breves esta tarde, sobre el interior y oeste de Puerto
Rico.

.Inundaciones...Las fuertes lluvias pueden ocasionar inundaciones
urbanas y de riachuelos.

.Corrientes Marinas...Existe un riesgo moderado de corrientes marinas
para todas las islas.

.Dias dos hasta el siete...jueves a martes

Aguaceros en la tarde el jueves puden ocasionar inundaciones urbanas
y de riachuelos sobre el suroeste de Puerto Rico. Un riesgo moderado
de corrientes marinas prevalecera a traves de las playas del norte y
este de las islas hasta el fin de semana. Se pronostica que el
viento y oleaje aumenten gradualmente durante el fin de semana hacia
la proxima semana.

.Comunicado sobre informacion reportada por observadores...

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

AMZ715-725-VIZ001-002-250815-
San Tomas, San John e Islas Adyacentes-
Santa Cruz-Aguas cercanas del Atlantico y aguas
costeras adyacentes del Caribe-
409 AM AST miercoles 24 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

.Corrientes Marinas...Existe un riesgo moderado de corrientes marinas
para las playas del norte de San Tomas y este de Santa Cruz.

.Dias dos hasta el siete...jueves a martes

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 gradualmente durante el fin de semana hacia la
proxima semana.

.Comunicado sobre informacion reportada por observadores...

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