Areal Flood Warning 3, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
949 PM AST Wed Apr 12 2017

.UPDATE...The 13/00Z sounding has come back with a wet 1.90 inches
of precipitable water as some showers continue over Puerto Rico.
The low pressure about 500 miles north of Puerto Rico has
developed sufficiently that a frontal boundary is now clearly
seen. Currently this boundary extends northeast from Isabela. Over
the Atlantic thunderstorms formed along the boundary and are
moving east at 10 knots. Some showers are also noted around and
north of the northern U.S. Virgin Islands and around and just east
of the Leeward Islands in southerly flow. Most of the models hold
this boundary close to--or over--Puerto Rico such that winds
north of Puerto Rico and north of a line extending northeast of
Cabo San Juan are northerly or westerly. Winds south of the
interior of Puerto Rico and over the U.S. Virgin Islands are
southeasterly tomorrow at mid day. Moisture will continue at
levels similar to today, but wind flow will be more favorable to
showers and thunderstorms over the interior. Given the southwest
trajectory of the low driving the flow, and the fact that the
models have been underestimating total columnar moisture, and the
intruding spear of divergence aloft at 250 mb intersecting western
PR at 13/18z, we expect another similar day of showers and
flooding. The GFS is suggesting that the proximity of the drier
air behind the frontal boundary formed by the low to the north
will lower the moisture, but this may not be the case in
practicality. Emergency managers should expect another very
active afternoon for Puerto Rico Thursday.

&&

.AVIATION...A frontal bndry has formed and extended NE from TJBQ
at 13/00z with thunderstorms and frequent LTGICCW about 55 miles
north of TJNR movg E/10 kt. This bndry will move little and settle
over PR by 13/15Z. At 13/01Z SHRA are moving thru the fcst area
along the north coast and through the interior. Some mtn
obscurations can be expected along with periods of MVFR in the
vcnty of the SHRA however conds are expected to improve over PR
with VFR beginning to prevail everywhere there. VCSH arnd USVI
thru 13/02z but VFR should prevail. Brief pds of MVFR in TNCM/TKPK
in SHRA for CIGS thru at least 13/22Z.

Aft 13/16Z +SHRA with psbl TSRA will dvlp over PR such that most
of the interior will be MVFR or less til byd 13/22Z with hir trrn
obscured. Winds alf bcm SW-W abv FL110 and max wins are 80 kt from
FL350-410.

&&

.MARINE...Seas continue to remain below 5 feet in the Atlantic and
below 4 feet in the Caribbean, but the boundary mentioned above
will keep showers and thunderstorms active over the local waters
and this activity may move into the Caribbean Thursday night. The
next significant wave/swell event is delaying and will begin
Sunday night into Monday.

&&

.PREV DISCUSSION... /issued 212 PM AST Wed Apr 12 2017/

SYNOPSIS...
A deep layer low and plenty of tropical moisture are enhancing
shower and thunderstorm activity across the region. This weather
pattern will be slowly weakening through the work week. However,
as the surface low, now at around 600 mi north of PR/USVI, drift
northward will advect plenty of tropical moisture from the south
into the local region by the upcoming weekend. As a result, expect
showers and thunderstorms each day of this week.

SHORT TERM...
A trof pattern with plenty of tropical moisture will continue to
enhance showers and thunderstorms across the islands. In general,
most of the activity is expected along and to the north of the
Cordillera Central of Puerto Rico. Heavy rainfall will likely to
result in urban flooding as well as rises along small streams and
rivers, as well as mudslides in areas of steep terrain. Elsewhere,
due to the unstable conditions and the available moisture showers
and t-storms can not be ruled out. This activity is expected to
slowly diminish around sunset, leaving partly to mostly clear
skies. However, under the southerly wind flow, passing showers are
possible across the local waters, south and east coast of Puerto
Rico and St Croix overnight.

LONG TERM...from previous discussion...
The long range models are now starting to indicate that the bulk
of the moisture and shower activity for this weekend will be much
closer to the local islands compared to what they were suggesting
a few days ago. They still insist that the bulk of the moisture
will be just to the south of the local islands, over the Caribbean
waters but they are now hinting for deeper moisture over the USVI
and PR and not just over the Caribbean waters. Because of the
recent change in the model forecast, the confidence is fairly low
as a slight change north or south of this moisture boundary would
mean a big difference in weather expected. However, the models
keep insisting in very deep moisture over the local islands by the
middle of next week, even though that is very far into the
forecast period, the models have been consistent with that.

AVIATION...Passing SHRA are expected across the local waters, and
some of this SHRA are possible across TJPS/TIST/TISX/TNCM/TKPK
through the fcst prd. Mtn Top obscr ovr/along the Cordillera
Central will result in MVFR/IFR conditions at TJBQ/TJSJ thru at
least 12/23z. Southerly winds at 5 to 10 knots with sea breeze
variations expected today. Calm to light and variable winds aft
12/23z.

MARINE...Tranquil marine conditions with 2 to 4 feet and
southerly winds at 10 to 15 knots. Seas will gradually increase
tonight and Thursday.

For the beach goers...a low risk of rip current for today. The
risk of rip current is expected to increase to moderate mainly
along the Atlantic coastline.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  76  87  76  87 /  40  70  20  20
STT  74  84  75  85 /  40  30  30  30

&&

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

SHORT TERM...WS
LONG TERM....CAM

Perspectivas sobre condiciones peligrosas del tiempo
Servicio Nacional de Meteorologia San Juan PR
1000 AM AST miercoles 12 de abril de 2017

AMZ710>745-PRZ001>013-130200-
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
aguas mar afuera del Atlantico y aguas costeras del Caribe-
1000 AM AST miercoles 12 de abril de 2017

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

.Dia uno...Hoy y esta noche

.Trondas...Existe un potencial de tronadas con lluvias fuertes y
vientos en rafaga breves esta tarde a traves de porciones del
interior y norte de Puerto Rico incluyendo partes del area
metropolitana de San Juan.

.Inundaciones...Lluvias fuertes podrian resultar en inundaciones
urbanas y de riachuelos al igual que inundaciones a lo largo de
algunos rios mayores. Deslizamientos de lodo y escombros seran
posibles en areas de terreno empinado.

.Dias dos a siete...jueves a martes

Aguaceros y tronadas localmente inducidos podrian causar
inundaciones urbanas y de riachuelos en Puerto Rico hasta el jueves.
Un riesgo moderado de corrientes marinas se espera a traves de las
costas del Atlantico el jueves y durante el fin de semana entrante
aumentando a alto temprano la semana proxima.

.Comunicado sobre informacion reportada por observadores...

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

AMZ715-725-VIZ001-002-130200-
San Tomas, San John e islas adyacentes-Santa Cruz-
Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe-
1000 AM AST miercoles 12 de abril de 2017

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

.Dia uno...Hoy y esta noche

.Tronadas...Existe un potencial de tronadas aisladas,
particularmente a traves de las aguas regionales.

.Dias dos a siete...jueves a martes

Un riego moderado de corrientes marinas se espera durante el fin de
semana entrante aumentando a alto la semana proxima.

.Comunicado sobre informacion reportada por observadores...

Activacion amplia de observadores no sera necesaria.