Tropical Storm Warning 1013, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
444 AM AST Fri Aug 21 2020

.SYNOPSIS...A tropical wave, which caused numerous showers and
thunderstorms overnight, will move away this morning. After a
temporary improvement later this morning into early this
afternoon, weather conditions will once again deteriorate
significantly later this evening through Saturday as Tropical
Depression Thirteen approaches the area. The worst conditions are
expected on Saturday with very heavy rainfall activity, gusty
winds, and hazardous marine conditions.

&&

.SHORT TERM...Today through Sunday...

Tropical Depression 13 will be the dominant influence on weather
conditions in Puerto Rico and the U.S. Virgin Islands during the
period. Showers will continue today in an unstable and very moist
environment under the influence of an upper level trough moving
through the Caribbean Sea to the south. For tonight into
Saturday...Tropical Depression Thirteen, is expected to approach
the islands and pass through the northern part of our Outer
Atlantic waters. It continues to remain disorganized with a
dubious center of circulation. The National Hurricane Center is
forecasting it to slowly gain strength and become a tropical storm
early Saturday morning. A band of rich moisture has already
passed through the area overnight and the next band of moisture
more closely associated with TD 13 is expected to move into the
U.S. Virgin Islands this afternoon and Puerto Rico a few hours
later. These showers and thunderstorms will slowly begin to
increase in frequency and intensity as we move into Saturday
morning when the system is forecast to be close to the local
islands. Tropical storm conditions are currently expected for the
Atlantic Offshore waters and there is a Tropical Storm Watch in
effect for the entire area.

The main impact of this cyclone will be the flooding rains,
therefore, a Flash Flood Watch is in effect for Puerto Rico and the
U.S. Virgin Islands between Saturday morning and Sunday evening.
Rainfall totals associated with the event are forecast to range
between 3 and 6 inches, mainly across the south and east sections of
Puerto Rico. As a result, there is a high risk for flash flooding,
and mudslides in areas of steep terrain. Some main rivers may
overflow their banks and tributaries.

.LONG TERM...Monday through Saturday...

Monday is expected to be unsettled. A retrogressing mid to upper-
level low is expected to induce a surface trough. This feature
along deep moisture will combine to result in enhanced shower and
thunderstorm activity across the local area, especially Monday
afternoon and evening into at least the first part of Tuesday.
Given that the soils will most likely be saturated from the heavy
rainfall activity left by Tropical Depression Thirteen, there is a
potential for urban and small stream flooding to materialize.
Improving weather conditions are expected on Wednesday, as drier
air moves in. Weather conditions may deteriorate once again late
Wednesday and Thursday, as a tropical wave may move across.
However, model guidance currently is in disagreement as to how
robust this tropical wave will be as the ECMWF model favors a weak
wave passage while the GFS model favors a more robust wave.
Either way, after the passage of this wave, improving weather
conditions are expected at the end of the long-term period.

&&

.AVIATION...Mainly VFR conditions expected. However, brief
MVFR conditions possible with VCSH/VCTS at TJBQ/TJSJ. Aft 21/18Z
areas of TSRA.SHRA will increase and begin to affect most of the
area and TAF sites. Winds will increase from light and variable over
PR and from 5-10 knots USVI and Leeward Islands to NE 10-20 knots by
21/18Z. Mtn obscurations. Maximum winds ENE 25-35 kt btwn FL 280-
375.

&&

.MARINE...Seas are expected to remain below 6 feet through this
afternoon, however, they will rapidly deteriorate later tonight
and during the upcoming weekend as Tropical Depression Thirteen,
which is forecast to become a tropical storm, moves just north of
the area. At this time, the highest seas are expected across the
offshore Atlantic waters with up to 16 feet possible. Tropical-
storm-force winds are also expected to impact the offshore
Atlantic waters. A tropical watch is in effect Friday evening
through Saturday evening.

There is a moderate risk of rip currents across the northern
beaches of Puerto Rico as well as across the eastern beaches of
Culebra, Vieques, and Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  89  80  84  77 /  60  70  80  80
STT  90  82  84  78 /  60  60  70  60

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Flash Flood Watch from Saturday morning through Sunday evening
     for Central Interior-Culebra-Eastern Interior-Mayaguez and
     Vicinity-North Central-Northeast-Northwest-Ponce and
     Vicinity-San Juan and Vicinity-Southeast-Southwest-Vieques-
     Western Interior.

     Tropical Storm Watch for Central Interior-Culebra-Eastern
     Interior-Mayaguez and Vicinity-North Central-Northeast-
     Northwest-Ponce and Vicinity-San Juan and Vicinity-
     Southeast-Southwest-Vieques-Western Interior.

VI...Flash Flood Watch from Saturday morning through Sunday evening
     for St Croix-St.Thomas...St. John...and Adjacent Islands.

     Tropical Storm Watch for St Croix-St.Thomas...St. John...and
     Adjacent Islands.

AM...Tropical Storm Watch for Caribbean Waters of Puerto Rico from 10
     NM to 17N-Anegada Passage Southward to 17N-Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N-Coastal Waters
     of Northern Puerto Rico out 10 NM-Coastal Waters of
     Northern USVI and Culebra out 10 NM-Coastal Waters of
     Northwestern Puerto Rico out 10 NM-Coastal Waters of
     Southern Puerto Rico out 10 NM-Coastal Waters of Southern
     USVI Vieques and Eastern Puerto Rico out 10 NM-Coastal
     Waters of Southwestern Puerto Rico out 10 NM-Mona Passage
     Southward to 17N.

&&

SHORT TERM...WS
LONG TERM....GL
PUBLIC DESK...ERG

Perspectivas sobre Condiciones Peligrosas del Tiempo
Servicio Nacional de Meteorologia San Juan PR
413 AM AST viernes 21 de agosto de 2020

AMZ710>745-PRZ001>013-220800-
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-
413 AM AST viernes 21 de agosto 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 lluvia
moderada a localmente fuerte y vientos en rafaga breves esta tarde a
traves de Puerto Rico y las Islas Virgenes Estadounidenses y las
aguas locales.

.Inundaciones...Lluvias fuertes pudieran resultar en inundaciones
urbanas y de riachuelos.

.Viento...Vientos sostenidos en exceso de 40 MPH (35
nudos) son posibles a traves de la porcion norte de las aguas mar
afuera del Atlantico esta noche.

.Oleaje...Se espera oleaje peligroso de hasta 16 pies a traves mar
afuera del Atlantico mas tarde esta noche.

.Corrientes marinas...Existe un riesgo moderado de corrientes
marinas para la costa norte de Puerto Rico, todo Culebra y el
extremo este de Vieques.

.Calor...Humedad mas alta y temperaturas encima de lo normal
causaran que los indices de calor alcancen hasta 105 grados
Fahrenheit en la mayoria de las elevaciones mas bajas.

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

Fuertes vientos en rafagas, un riesgo moderado a alto de corrientes
marinas y periodos de fuertes lluvias son posibles para Puerto Rico,
Culebra y Vieques. Condiciones de tormenta tropical son posibles el
sabado en las aguas mar afuera del Atlantico.

.Comunicado sobre informacion reportada por observadores...

No se anticipa activacion 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-VIZ001-002-220800-
San Tomas, San John e Islas Adyacentes-Santa Cruz-Aguas cercanas del
Atlantico y aguas costeras adyacentes del Caribe-
413 AM AST viernes 21 de agosto 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 lluvia
fuerte y vientos en rafaga breves esta tarde y durante la noche a
traves de las Islas Virgenes Estadounidenses.

.Inundaciones...Lluvias fuertes pudieran resultar en inundaciones
urbanas y de cunetas.

.Viento...Vientos sostenidos en exceso de 40 MPH (35 nudos) son
posibles a traves de la porcion norte de las aguas mar afuera esta
noche.

.Oleaje...Se espera oleaje peligroso de hasta 16 pies a traves de
las aguas mar afuera del Atlantico mas tarde esta noche.

.Corrientes marinas...Existe riesgo moderado de corrientes marinas
para la mayoria de las playas de San Tomas, San John y el extremo
este de Santa Cruz.

.Calor...Humedad mas alta y temperaturas encima de lo normal
causaran que los indices de calor alcancen hasta 105 grados
Fahrenheit en la mayoria de las elevaciones mas bajas.

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

Fuertes vientos en rafagas, un riesgo moderado a alto de corrientes
marinas y periodos de fuertes lluvias son posibles para las Islas
Virgenes Estadounidenses. Condiciones de tormenta tropical son
posibles el sabado en las aguas mar afuera del Atlantico.

.Comunicado sobre informacion reportada por observadores...

No se anticipa activacion 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.