Rip Current in Puerto Rico, September 1, 2020

Area Forecast Discussion
National Weather Service San Juan PR
1139 AM AST Tue Sep 1 2020

.UPDATE...
No change to inherited short term forecast package and reasoning
at this time except for some minor adjustments to the weather and
pops forecast grids, based on the timing of the weather activity.
Very moist and unstable 01/12Z TJSJ upper air sounding as the
Tropical Wave and accompanying plume of moisture continued to
move across the region. A slow but gradual drying of the local
airmass is still expected later tonight through Wednesday with
increasing trade winds and the arrival of another surge of Saharan
dust, with a low to moderate concentration forecast to linger
across the region at least into Saturday. Locally and diurnally
induced afternoon convection will remain possible across the
islands each day with passing morning showers to affect the north
and east coastal areas carried by the prevailing easterlies.

&&

.AVIATION UPDATE...Tropical wave crossing the northeastern
Caribbean today will bring SCT-BKN lyrs nr FL025...FL050...FL080
with SHRA/ISOLD TSRA ovr regional waters and en route btw islands.
Locally induced aftn SHRA/Isold TSRA also psbl vcty at most of
local terminals durg prd til 01/23z. Isold Tops btw FL250-FL300
w/Isold TSRA. Sfc wnds fm E-SE 10-15 kts w/ocnly hir gust
accompanying passing SHRA.L/LVL wnds fm E-SE 15.20 kts BLO FL250.

&&

.MARINE UPDATE...No change to previous marine discussion.
Tropical wave will continue to cross the regional waters today
with trade winds forecast to gradually increase through
Wednesday. As a result ,choppy and hazardous seas will continue
through a least Wednesday. Small Craft Advisories will be in
effect for portions of the local Atlantic and Caribbean waters and
passages. Small craft operators should exercise caution
elsewhere.

&&

.PREV DISCUSSION... /issued 531 AM AST Tue Sep 1 2020/

SYNOPSIS...

A tropical wave will bring showers and thunderstorms across the
area today. Tropical moisture will continue across the region
through at least Wednesday. Then, an upper level trough will
increase instability once again Thursday and Friday. However, a
dry air mass with Saharan dust will filters from the east
Thursday and early Friday, but patches of moisture will reach the
islands at times.

SHORT TERM...Today through Thursday...

The axis of a tropical wave is moving over the region today.
Total precipitable water (TPW) derived from the satellite imagery
associated with the aforementioned disturbance range between 2.0
and 2.1 inches. This feature will enhanced the potential for
shower and thunderstorm activity over Puerto Rico and the US.
Virgin Islands today. According to the Radar Doppler shower
activity is expected to continue over local waters and move to
coastal sections of Puerto Rico an the U.S. Virgin Islands in the
morning hours. Then, shower and thunderstorm activity are forecast
to develop over northwestern, western and interior sections of
Puerto Rico during the afternoon. Urban and small stream flooding
across the islands is expected with the strongest activity.

The lingering moisture will continue to promote shower and
thunderstorm activity across the local waters through at least
Wednesday morning. A more drier air mass with Saharan Dust
particles are expected to filter into the region on Wednesday. At
the upper levels, a TUTT-Low will move westward across the
northeast Caribbean Wednesday through Friday. The islands of
Puerto Rico and the U.S. Virgin Islands will remain in the
subsidence side of it on Wednesday. However, as this upper level
feature moves westward, instability is forecast to increase over
Puerto Rico and the U.S. Virgin Islands after Thursday. Although
instability will increase, the limiting factor will be the
available moisture, which is forecast to be limited.

LONG TERM...Friday through Wednesday...

Model guidance is suggesting lingering dust particles across the
islands early Friday morning. However, the upper-level feature
will continue to migrate westward over Hispaniola, increasing
instability and inducing a surface trough which is forecast to
lift tropical moisture across the islands of Puerto Rico and some
over the U.S. Virgin Islands. Under this weather pattern, expect a
good chance to observe showers and thunderstorms, especially
overnight/early Friday morning and in the afternoon hours. The
limiting factor will be the timing of the moisture arrival and if
it coincides with the peak of instability.

As the upper-level trough moves westward over the Windward
Passage, between Haiti/Cuba, stable weather conditions will be
possible Saturday and Sunday. However, patches of moisture
embedded in the trades will increase the chance to observe
overnight/early morning showers across the windward sections of
PR/USVI followed by afternoon convection across the western
portions of the islands.

Model guidance is suggesting a tropical wave approaching the
islands Monday or Tuesday, and another one for Wednesday or
Thursday. At this time, the most robust wave between these two
tropical disturbances seems the one for mid-week. It's too early
to determine the effects that would have these systems across the
islands. However, interests in Puerto Rico and the U.S. Virgin
Islands should monitor the behavior in the Tropical Atlantic.

AVIATION...

A tropical wave will bring SHRA/-SHRA across the islands today.
Isold-TSRA will remain possible across the local waters and some
of them could affect the vicinity of TIST/TJSJ/TISX through the
morning hours. TSRA/+SHRA will develop across the mountains and
over western PR btwn 1/16-23z and could impact JBQ/JSJ. Calm to
light and VRB winds will persist through 01/13z, then will prevail
mainly from the E-ENE between 10-15 kts with higher gusts and sea
breeze variation.

MARINE...
Mariners should exercise caution across the regional waters as a
tropical wave continues to produce showers and thunderstorms. In
addition, a wind surge will increase seas up to 7 feet across the
Atlantic Offshore waters and a Small Craft Advisory is in effect
from 8 am this morning through at least Wednesday evening.
Mariners can expect seas between 3 and 6 feet and winds between 15
and 20 knots, elsewhere. Seas will also increase across the
Anegada Passage and surrounding waters at up to 7 feet from this
evening through Wednesday morning. Seas will subside after mid-
week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  88  78  89  78 /  50  40  40  40
STT  88  79  90  79 /  50  40  30  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...VI...None.
AM...Small Craft Advisory from 8 PM this evening to 8 AM AST
     Wednesday for Caribbean Waters of Puerto Rico from 10 NM to
     17N-Anegada Passage Southward to 17N-Coastal Waters of
     Southern USVI Vieques and Eastern Puerto Rico out 10 NM.

     Small Craft Advisory until 8 PM AST Wednesday for Atlantic
     Waters of Puerto Rico and USVI from 10 NM to 19.5N.

&&

SHORT TERM...RAM
LONG TERM....TW
PUBLIC DESK...ERG

Perspectivas sobre Condiciones Peligrosas del Tiempo
Servicio Nacional de Meteorologia San Juan PR
515 AM AST martes 1 de septiembre de 2020

AMZ710>745-PRZ001>013-020915-
San Juan y Vecindad-Noreste-Sureste-Este Interior-Norte Central-
Interior Central-Ponce y Vecindad-Noroeste-Oeste Interior-Mayaguez y
Vecindad-Suroeste-Culebra-Vieques-Aguas cercanas y mar afuera del
Atlantico y Caribe-
515 AM AST martes 1 de septiembre de 2020

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 vientos en rafaga esta tarde a traves de sectores del noroeste e
interior de Puerto Rico.

.Inundaciones... Fuertes lluvias podrian generar inundaciones
urbanas y de pequenos riachuelos.

.Vientos...Se esperan vientos sostenidos en exceso de 20 MPH (17
nudos) a traves de las aguas locales mar afuera.

.Oleaje... Se espera oleaje vigoros/picado de hasta 7 pies se
esperan a traves de las aguas mar afuera el Atlantico.

.Corrientes Marinas... Existe un riesgo moderado de corrientes
marinas a traves de las costas del norte de Puerto Rico.

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

Humedad residual continuara generando actividad de aguaceros el
miercoles en la manana. Una vaguada en los niveles altos se espera
que llegue a la region el jueves y aumente el potencial de tronadas
y de inundaciones.

.Comunicado sobre informacion reportada por observadores...

No se anticipa activacion 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-VIZ001-002-020915-
San Tomas, San John e Islas Adyacentes-Santa Cruz-Aguas cercanas del
Atlantico y aguas costeras adyacentes del Caribe-
515 AM AST martes 1 de septiembre de 2020

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

.Dia Uno...Hoy y esta noche

.Tronadas... Existe una probabilidad de tronadas con fuertes lluvias
y vientos en rafaga esta tarde a traves de sectores las Islas
Virgenes Estadounidenses.

.Inundaciones... Fuertes lluvias podrian generar inundaciones
urbanas y de pequenos riachuelos.

.Vientos...Se esperan vientos sostenidos en exceso de 20 MPH (17
nudos) a traves de las aguas locales mar afuera.

.Oleaje... Se espera oleaje vigoros/picado de hasta 7 pies se
esperan a traves de las aguas mar afuera el Atlantico.

.Corrientes Marinas...Existe un riesgo moderado de corrientes
marinas a traves de las costas del este de Santa Cruz.

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

Humedad residual continuara generando actividad de aguaceros el
miercoles en la manana. Una vaguada en los niveles altos se espera
que llegue a la region el jueves y aumente el potencial de tronadas
y de inundaciones.

.Comunicado sobre informacion reportada por observadores...

No se anticipa activacion de observadores. 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.