Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 231953

Area Forecast Discussion
National Weather Service San Juan PR
353 PM AST Mon Oct 23 2017

.SYNOPSIS...Strong surface high pressure will remain anchored across the west
and central Atlantic to maintain a moderate east to southeast
trade wind flow through the end of the work week. A weak tropical
wave is forecast to enter and move across the eastern Caribbean by
mid week. A low to mid level trough will approach the region
during the weekend.


.SHORT TERM...Tonight through Wednesday...
Modest low level moisture and dry air aloft favoring strong morning
insolation coupled with low 500 mb temperatures create an unstable
atmosphere for afternoon thunderstorms today and Tuesday.
Convection will die shortly after sunset each day. The northerly
upper level jet over Puerto Rico around an upper level low just
north of the Leeward Islands will also increase ventilation where
convergence/divergence remains neutral. The low will move southeast
into the Windward Islands Wednesday and the jet will shift with it,
but better moisture at most levels will increase showers and
thunderstorms over the area then. Easterly winds at the surface will
shift to east southeast midday on Wednesday and shower and
thunderstorms will then focus more in northwest Puerto Rico. The U.S.
Virgin Islands will continue to see isolated showers and streamers
downstream from the islands.

.LONG TERM...Thursday through Tuesday...
An upper level ridge will remain across the local area through
the weekend. However, at lower level, an increase in moisture is
expected Saturday and Sunday as a low to mid level trough moves
through the region. By early next week, the upper ridge will be
eroded by an upper level trough which will retrograde west across
the local region.


.AVIATION...Mostly VFR conditions expected across all terminals
throughout the forecast period, however TSRA ovr wrn PR will bring
MVFR/IFR in lwr CIGS/VSBYS and some mtn obscurations. E winds of 10-
15 KT excpt for sea breeze influences diminishing below 12 KT after
23/00z. SHRA dvlpg aft 24/06Z in easterly flow and will move onshore
in ern PR and over USVI.  Max winds north 50 kt nr FL410 incrg to 70
kt by 24/12Z.


.MARINE...Seas up to 5 feet and winds up to 15 knots are expected
across the coastal waters.


SJU  77  88  76  88 /  40  20  30  30
STT  77  87  78  87 /  20  10  30  30




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