Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 170147

Area Forecast Discussion
National Weather Service San Juan PR
947 PM AST Wed Aug 16 2017

.UPDATE...Numerous showers with thunderstorms affected the local
islands tonight. Heavy rainfall with strong gusty winds were
observed with the heaviest activity. This activity is associated
with the leading edge of an active tropical wave which will
approach the local islands overnight. As a result, active weather
will continue through at least Thursday afternoon. Forecast is on
track with ongoing weather situation.


.AVIATION...Mainly VFR conditions will prevail across most TAF
sites through at least 17/12Z. VCSH are expected across most TAF
sites.  Periods of MVFR conditions can be expected across TNCM
and TKPK in TSRA. Low level winds will continue mainly east at 10
to 15 kts with higher gusts.


.MARINE...Seas up to 7 feet and winds up to 20 knots are expected
to continue through at least Thursday night. Showers and
thunderstorms will maintain hazardous marine conditions across the
local waters. Refer to marine products for latest information.


.PREV DISCUSSION... /issued 438 PM AST Wed Aug 16 2017/

SYNOPSIS...A tropical wave just across the eastern Caribbean
will move across the forecast area tonight through Thursday. TUTT
low will continue just to the west- northwest of the forecast area
through Friday as an upper ridge builds from the north. Saharan
air layer will gradually diminish tonight ahead of the tropical

SHORT TERM...Tonight through Friday...
A mid to upper level ridge is expected to build across the
forecast area Thursday night, as a trough aloft/TUTT across the
northeast Caribbean shifts westward. At lower levels, a broad
high pressure across the central Atlantic will continue to produce
a moderate to fresh easterly winds through the forecast period.
An active tropical wave across the Lesser Antilles this afternoon
will continue to move westward moving across the local islands
tonight and Thursday. The moisture associated with the leading
edge of the wave in combination with daytime heating and local
effects will continue to induce the development of shower and
thunderstorm activity across the U.S. Virgin Islands, Vieques,
Culebra, Puerto Rico and the surrounding waters for the rest of
this afternoon and evening. The chance for showers and thunderstorms
will increase across the forecast area tonight into Thursday due
to the proximity of TUTT low and the tropical wave moving across
the local islands.

Urban and small stream flooding likely. Shower and thunder
development across west Puerto Rico Thursday afternoon will be
dependent on cloud cover. As the tropical wave moves away and an
upper level ridge builds, a fair weather pattern is then expected
to prevail on Friday.

LONG TERM...Saturday through Wednesday...PREVIOUS DISCUSSION...
In the medium range, an area of low pressure near 48W longitude,
which the National Hurricane Center is giving a 40% chance of
formation during the next 5 forecast to move across the
Caribbean Sea between Friday and Saturday...and remain south of
the islands. Another area of low pressure near 35W longitude,
that NHC is also giving a 40% chance of formation during the next
5 days, is currently expected to move close to the forecast area
late in the weekend. In the long range, latest runs of both GFS
and ECMWF runs indicated a surface low pressure area passing well
to the northeast of the forecast area by midweek.

AVIATION...Approaching tropical wave is bringing SHRA/TSRA to the
local area. Intermittent brief moment of SHRA/TSRA over the local
terminals is expected, some of which could cause at least MVFR conds
for brief moments at a time. Mainly VCSH/VCTS written on TAF due to
uncertainty on timing, AMD with TEMPO as necessary. Winds will
remain at about 15-20KT with occasional gusts. CIGS will be at about
FL040 but lower in SHRA/TSRA. Wx conditions across the local
terminals to be unsettled through Thursday night.

MARINE...Seas are expected to increase tonight between 6-8 feet
across the Anegada Passage and across both Atlantic and Caribbean
offshore waters through at least Thursday. Small craft advisories
are in effect. East to northeast winds between 15 to 20 knots will
prevail tonight. Squally weather is possible tonight and Thursday
as the wave moves across the local area. A high risk of rip
currents is in effect for northwest and north central beaches of
Puerto Rico and for St. Croix.


SJU  79  88  80  87 /  60  60  20  20
STT  80  89  80  92 /  60  60  30  20


PR...     High Rip Current Risk until 6 AM AST Thursday for North Central-
     Northwest-Western Interior.

VI...Small Craft Advisory until 8 PM AST Thursday for St.Thomas...St.
     John...and Adjacent Islands.

     High Rip Current Risk until 6 AM AST Thursday for St Croix.

AM...Small Craft Advisory until 8 PM AST Thursday for Anegada Passage
     Southward to 17N-Atlantic Waters of Puerto Rico and USVI
     from 10 NM to 19.5N-Coastal Waters of Northern USVI and
     Culebra out 10 NM-Coastal Waters of Southern USVI Vieques
     and Eastern Puerto Rico out 10 NM.

     Small Craft Advisory until 2 PM AST Thursday for Caribbean
     Waters of Puerto Rico from 10 NM to 17N-Mona Passage
     Southward to 17N.

     Small Craft Advisory from 2 AM to 2 PM AST Thursday for Coastal
     Waters of Northern Puerto Rico out 10 NM.



LONG TERM....JF is the U.S. government's official web portal to all federal, state and local government web resources and services.