Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 161002 CCA
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
542 AM AST Wed Aug 16 2017

.SYNOPSIS...A tropical wave just east of the Lesser Antilles will
move across the forecast area later 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 today ahead of the
tropical wave.


&&

.SHORT TERM...Today through Friday...A mid to upper level ridge
is expected to build across the forecast area Thursday night, as a
trough aloft/TUTT low which is now located across the northeast
Caribbean shifts westward. However, the ridge pattern aloft is
expected to be short-lived as trofiness returns to the local isles
on Sunday. At lower levels, a broad high pressure across the
central Atlantic will continue to yield moderate to fresh easterly
winds through the forecast period. The next tropical wave passage
is expected as soon as late tonight into Thursday.

Under this evolving pattern, expect fair weather conditions through
the morning hours followed by locally induced showers and
thunderstorms across southwest Puerto Rico in the afternoon. The
chance for showers and thunderstorms -squally weather type- will
increase across the forecast area late tonight into Thursday due to
the proximity of TUTT low and a tropical wave moving across the
eastern Caribbean.

At this time, the most active convection and the best chance for
heavy rainfall is across US Virgin Islands and eastern Puerto Rico
Thursday morning. 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...In the medium range, an
area of low pressure near 46W longitude, which the National
Hurricane Center is giving a 40% chance of formation during the next
5 days...is forecast to move across the Caribbean Sea between Friday
and Saturday...and remain south of the islands. Another area of low
pressure near 34W 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 as an open trough late in the weekend. In
the long range, both GFS and ECMWF 16/00z runs indicated a surface
low pressure area passing well to the northeast of the forecast area
by midweek.


&&

.AVIATION...VFR conds are expected at all TAF sites in the morning
with brief MVFR conds possible at JMZ/JPS in SHRA/TSRA btw 16/16-
22z. As a tropical wave moves across the eastern Caribbean,
SHRA/TSRA and MVFR conds are expected in and around the Leeward
terminals late this afternoon, spreading across the USVI terminal
and JSJ late tonight. Easterly winds 15-20 knots aft 16/13z.


&&

.MARINE...Seas are expected to increase later today ahead of the
tropical wave 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 today. Squally weather is
possible early on Thursday as the wave exits the local area. A
moderate to high risk of rip currents is expected for the next few
days across PR, Culebra, Vieques and St. Croix.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  87  79  88  80 /  30  60  60  20 STT  91  80  89  80 /  20  60
60  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None

VI...High Rip Current Risk through this afternoon for St Croix.

AM...Small Craft Advisory from 2 PM this afternoon to 8 PM AST
     Thursday for Anegada Passage Southward to 17N-Atlantic
     Waters of Puerto Rico and USVI from 10 NM to 19.5N.

     Small Craft Advisory from 8 PM this evening to 8 PM AST Thursday
     for 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 from 8 PM this evening to 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.

&&

$$

SHORT TERM...OM
LONG TERM....DS


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