Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 252017

Area Forecast Discussion
National Weather Service San Juan PR
417 PM AST Wed Apr 25 2018


An increase in low level moisture is expected tonight and
Thursday, with increasing rain chances tomorrow. A mid to upper
level ridge will build over the area late Thursday and prevail
across the region through early next week with fair weather and an
occasional shower.


.SHORT TERM...Tonight through Friday...

Mostly sunny skies prevailed over the U.S. Virgin Islands and
Puerto Rico today with easterly winds ranging from 5 to 15 mph.
Some showers were observed over the Atlantic waters but other than
those isolated showers today has been tranquil. A weakening
surface trough near the Lesser Antilles has pulled low level
moisture into the Caribbean and North Atlantic waters today with
the bulk of the moisture expected to reach the U.S. Virgin
Islands and Puerto Rico tonight and Thursday morning. As a result
an increase in showers with the possibility for isolated
thunderstorms is expected on Thursday. Early Friday a
strengthening upper and mid level ridge will build across the area
and prevail through the weekend with brisk easterly winds of 15
to 20 mph. Drier air and strong trade winds will limit shower
development across the area on Friday through the weekend.


A mid to upper level ridge will hold across the forecast area through
the weekend. This feature is expected to quickly erode early the next
workweek as a broad upper level trough establishes across the western
Atlantic and into the eastern Caribbean. The aforementioned trough
will promote moisture advection across the eastern Caribbean Wednesday
onwards. If the long term forecast holds, expect seasonably conditions
Saturday through Tuesday with locally induced afternoon showers
and a few isolated thunderstorms across the western interior and
west areas of Puerto Rico each day. The chance for showers and
thunderstorms are expected to increase by midweek under deep
tropical moisture and plenty of upper level dynamics associated
with the upper level trough.



Mainly VFR conditions are expected to prevail early in
the forecast period. SHRA expected to increase from the east across
the USVI terminals by 26/06z then by 26/12z across the eastern PR
terminals. This will be followed by TSRA developing after 16z across
the interior and western PR. Tempo MVFR to brief IFR possible with
afternoon activity at TJMZ/TJBQ. SCT-BKN cigs btw FL030-FL060 and
mtns obscd expected across the PR terminals on Thursday. Winds will
continue from the ESE blo FL100 at 8-18 kt with sea breeze
variations at the northern and western terminals aft 26/14z.



Seas are expected to range from 3 to 4 feet across the coastal
waters while the offshore waters and passages will be near 3 to 5
feet. East southeast winds 10 to 20 kts will prevail over the next
several days. There is a moderate risk of rip currents across the
northern beaches of Puerto Rico today.


SJU  76  89  76  89 /  20  40  20  20
STT  76  87  76  87 /  40  20  20  20




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