Area Forecast Discussion
Issued by NWS San Juan, PR

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394
FXCA62 TJSJ 181442
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1042 AM AST Mon Dec 18 2017

.UPDATE...Variably cloudy skies prevailed during the morning hours
as passing trade wind showers affected portions of the USVI and
the north and east sections of PR. This trade wind shower pattern
will continue through the rest of the day. Breezy conditions will
keep pushing showers inland across the interior sections of PR
this afternoon. Only minor changes were made to previous forecast.


&&


.AVIATION Update...SHRA will continue to move across the USVI/PR
terminals through the forecast period. Tempo MVFR cigs are
possible with the passing SHRA. Latest 18/12z TJSJ upper air
sounding indicated NE winds at 13-24 kts below FL050.


&&

.MARINE Update...Coastal buoys were indicating seas between 3-5
feet and northeast winds at 10-15 kts with higher gusts. Small
crafts advisories are in effect until 2 pm this afternoon.
However, winds up to 20 knots and/or seas up to 6 feet will
continue for the next few days...therefore small craft operators
should continue to exercise caution. High risk of rip currents
continue for the northern beaches of PR including Culebra.
Moderate risk elsewhere.


&&

.PREV DISCUSSION... /issued 532 AM AST Mon Dec 18 2017/

SYNOPSIS...
Puerto Rico and the U.S. Virgin Islands weather will be controlled by
a mid to upper level ridge through Friday. On thursday a trough
of low pressure will move into the Atlantic waters and cause the
mid to upper level high pressure in the Atlantic to weaken. This
will cause unsettled weather across Puerto Rico and the U.S.
Virgin Islands through the Sunday.

Short Term...Today through Wednesday...
A surface high pressure over the western Atlantic will tight the
local pressure gradient inducing a northeast wind flow across the
islands. The breezy northeasterly wind flow will bring patches of
clouds and showers mainly across the U.S. Virgin Islands and the
northern and eastern portions of Puerto Rico at times. A ridge
pattern aloft will limit vertical development. The upper to mid
level ridge will slowly erodes after Wednesday as a TUTT low sink
from the northeast over the Northeastern Caribbean.

LONG TERM...Friday through Thursday...
The mid to upper level ridge that has brought somewhat fair
weather with an occasional isolated shower will weaken ahead of a
cold front that will move into the north Atlantic waters. The
front will push an upper level trough near the forecast area on
Friday. Friday will be a transition day from quiet weather to a
more unsettled pattern due to an increase in tropical moisture
across Puerto Rico and the U.S. Virgin Islands. The GFS and ECMWF
models are indicating that this active pattern will remain through
Christmas due to an tutt low that might cut off near Puerto Rico
and the U.S. Virgin Islands. At this time it`s something to keep
an eye on over the next several days.

Aviation...
Trade wind showers will continue to affect TIST/TISX
TJSJ/TJBQ through 18/16z. As a result SCT-BKN cigs at FL025-FL060
are possible. All taf sites are expected to receive periods of -
SHRA/SHRA btwn 18/19-23z. Surface winds will continue at 10-15 kt
increasing at 15-20 kt with higher gusts aft 18/13z.

MARINE...
Northeasterly wind flow will continue over the next several days.
This will result in choppy and rough seas across most of the
local waters ways. Small craft advisories will remain in effect
until later this afternoon. Seas will be 5 to 7 feet with
occasional seas up to 8 feet with winds 10 to 15 kts with higher
gusts. High rip current risk remains for the northern facing
beaches while moderate to low risk for the other areas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  83  77  85  77 /  40  40  40  50
STT  86  79  86  76 /  50  40  40  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for Culebra-
     North Central-Northeast-Northwest-San Juan and Vicinity-
     Southeast-Western Interior.

VI...Small Craft Advisory until 2 PM AST this afternoon for
     St.Thomas...St. John...and Adjacent Islands.

AM...Small Craft Advisory until 2 PM AST this afternoon for Anegada
     Passage Southward to 17N-Atlantic Waters of Puerto Rico and
     USVI from 10 NM to 19.5N-Caribbean Waters of Puerto Rico
     from 10 NM to 17N-Coastal Waters of Northern USVI and
     Culebra out 10 NM-Coastal Waters of Southern USVI Vieques
     and Eastern Puerto Rico out 10 NM-Mona Passage Southward to
     17N.

&&

$$

DS



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