Flash Flood Warning 117, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
921 PM AST Thu Sep 28 2017

.UPDATE...

Trimmed PoPs based on current satellite trends and short term
model guidance. Reduced PoPs overall and trended highest PoPs to
the VI. Coverage appears to increase area wide towards dawn then
high PoPs beginning Friday morning.

&&

.PREV DISCUSSION... /issued 830 PM AST Thu Sep 28 2017/

AVIATION...

Showers and isolated thunderstorms will increase overnight
beginning in the VI then impact PR beginning in the morning hours.
Will carry VFR outside of convection with temporary restrictions
to MVFR in or near showers/storms. Will maintain VCSH from the
previous TAFs and metwatch for amendments as needed. Winds
generally will be from the east at 10-15 mph.

PREV DISCUSSION... /issued 405 PM AST Thu Sep 28 2017/

...Heavy rain expected beginning Friday which will aggravate the
ongoing recovery and relief efforts on Puerto Rico. A FLASH FLOOD
WATCH is in effect for all islands...

SHORT TERM...

Mid level winds are becoming southeasterly on the backside of an
exiting upper trough which will allow deep easterly/southeasterly
flow to advect deeper moisture into the area from the southeast.
Regional satellite showers the beginning of the moisture moving
towards Antigua and the Virgin Islands. A general slow northwest
movement to this moisture plume is expected. Precipitation chances
will increase across the Virgin Islands tonight then across Puerto
Rico Friday. See the hydrology section for amounts and impacts.

There is a high risk of rip currents through Friday along the
northern Atlantic coastline of Puerto Rico and St. Croix with a
moderate risk on the southern coast. The Rip Current Statement
will continue through Friday afternoon due to dangerous northerly
swells continuing.

LONG TERM...

Deep tropical moisture will be in place this weekend as a weak
trough of low pressure moves westward across the islands. Periods
of heavy rainfall will be possible with models increasing
precipitable water values to just over 2.00" Friday and Saturday.
At this point, it appears that the best chance for heavy
precipitation will be Friday afternoon and evening and again on
Saturday. Locations that are still dealing with highly- saturated
soils are vulnerable to additional flooding this weekend,
especially near rivers and in low-lying areas. Recovery efforts
will need to keep a very close eye on thunderstorms during this
period, as additional flooding will be possible.

MARINE...

Moderate winds and seas will dominate across the area through the
weekend. Northerly swells continue to batter the northern sections
of the islands where small craft will need to exercise caution.
Showers and thunderstorms will become numerous beginning Friday with
winds and seas locally higher in and around stronger convection.

FIRE WEATHER...

Rain chances will increase beginning later tonight through early
next week as deep tropical moisture moves into the area. No fire
weather concerns.

HYDROLOGY...

Deep tropical moisture will overspread the islands beginning
tonight and continue through the weekend. The highest chance for
shower and thunderstorm activity is expected Friday afternoon into
Saturday, particularly across the interior and east Puerto Rico
as well as the U.S. Virgin Islands. Rainfall amounts of 2 to 4
inches with locally higher amounts likely each day. Soils are
already saturated and most of the rivers and small streams are
running above or well above normal levels, therefore there is a
high risk of river and small stream flooding as well as mudslides
in areas of steep terrain. Urban flooding is also likely across
low lying areas as well as poorly drained areas where water pumps
are not working at full capacity.

A FLASH FLOOD WATCH has been issued for all islands beginning
Friday morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  80  83  79  83 /  50  70  40  70
STT  81  82  80  81 /  50  70  50  70

&&

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

     Flash Flood Watch from Friday morning through late Sunday night
     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...High Rip Current Risk through Friday afternoon for St Croix.

     Flash Flood Watch from Friday morning through late Sunday night
     for St Croix-St.Thomas...St. John...and Adjacent Islands.

AM...Flash Flood Watch from Friday morning through late Sunday night
     for Coastal Waters OF Southwestern Puerto Rico out 10 NM-
     Coastal Waters of Northern USVI and Culebra 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.

&&

Update...99

Perspectivas sobre condiciones peligrosas del tiempo
Servicio Nacional de Meteorologia San Juan PR
Emitido por Servicio Nacional de Meteorologia Miami FL
423 PM AST jueves 28 de septiembre de 2017

AMZ710>745-PRZ001>013-292030-
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 lejanas a la costa del Atlantico y Caribe-
423 PM AST jueves 28 de septiembre de 2017

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

.Dia Uno...Esta Noche

Un Aviso de Inundaciones Repentinas permanece en efecto para la
Represa Guajataca debido a inundaciones repentinas potencialmente
peligrosas rio abajo del Rio Guajataca

.Corrientes marinas...Existe un riesgo alto de corrientes marinas
para la mayor parte de las playas del norte y noroeste de Puerto
Rico, excepto a lo largo de la costa sur y sureste, donde existe
riesgo moderado de corrientes marinas.

.Dias Dos a Siete...viernes a miercoles

Una Vigilancia de Inundaciones Repentinas esta en efecto comenzando
el viernes debido a fuertes lluvias anticipadas durante el fin de
semana. Acumulaciones de lluvia de 2 a 4 pulgadas cada dia con
acumulaciones localmente mas altas son probables. Esto empeorara la
situacion actual en Puerto Rico y resultara en preocupaciones
adicionales de inundaciones.

Riesgo elevado de corrientes marinas continuara durante el fin de
semana.

.Comunicado sobre informacion reportada por observadores...

No se anticipa activacion amplia de observadores, sin embargo, se
les exhorta a los observadores individuales a reportar inundaciones
y corrientes marinas al Servicio Nacional de Meteorologia en San
Juan.

AMZ715-725-VIZ001-002-292030-
San Tomas, San John e Islas Adyacentes-Santa Cruz-Aguas cercanas del
Atlantico y aguas costeras adyacentes del Caribe-
423 PM AST jueves 28 de septiembre de 2017

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

.Dia Uno...Esta Noche

.Corrientes marinas...Existe riesgo alto de corrientes marinas
para porciones del este de Santa Cruz. En el resto del area, riesgo
moderado de corrientes marinas continuara.

.Dias Dos a Siete...viernes a miercoles

Una Vigilancia de Inundaciones Repentinas esta en efecto comenzando
el viernes debido a fuertes lluvias anticipadas durante el fin de
semana. Acumulaciones de lluvia de 2 a 4 pulgadas cada dia con
acumulaciones localmente mas altas son probables.

Riesgo elevado de corrientes marinas pudiera continuar para la mayor
parte de las playas hasta el fin de semana.

.Comunicado sobre informacion reportada por observadores...

No se anticipa activacion amplia de observadores, sin embargo, se
les exhorta a los observadores individuales a reportar inundaciones
y corrientes marinas al Servicio Nacional de Meteorologia en San
Juan.