Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 232020

Area Forecast Discussion
National Weather Service San Juan PR
420 PM AST Wed Aug 23 2017

A TUTT low off to the northeast of the islands, over the Atlantic
Ocean, is forecast to sink into the region Thursday into the
upcoming week. Saharan air particles are expected to reach the
islands by Friday. In addition, a surface high pressure across the
Central Atlantic will induce a light to moderate trade wind flow
across the region.


The available moisture combined with the diurnal heating
induced showers and thunderstorms mainly to the west of mainland
Puerto Rico. Also, showers developed downwind from El Yunque into
the San Juan Metro Area without any significant impact. Showers
and thunderstorms are expected to vanish by sunset.

By Thursday, a TUTT low is forecast to sink over the region,
moisture is expected to increase and winds will veer from the
southeast. As a result, Hi-Res models continue to indicate
showers and thunderstorms across the northern half of Puerto Rico
with the heaviest activity across the Northwest Municipalities.
Meanwhile, fair weather conditions are expected across the U.S.
Virgin Islands with partly cloudy skies and some showers
developing downwind from the islands. Model guidance are
indicating the arrival of more Saharan dust particles by Friday,
which will result in hazy skies across the region.

LONG TERM...Saturday through Wednesday...Previous Discussion...

Upper level low will retrograde westward as upper level ridge
builds across the region. Moisture will increase somewhat by
Sunday as a tropical wave passes mainly south of the region.
Patches of low level moisture embedded in the trade winds will
affect the region Monday and Tuesday. A much drier air with
possible Saharan dust is forecast by computer models to approach
the region Wednesday next week.


VFR conditions expected across most of the TAF sites.
TJBQ and TJMZ may experience MVFR/IFR conds at times with the
afternoon TSRA thru 22Z. East winds of 10-15 knots will prevail
below FL150.


Tranquil marine conditions are expected to prevail through the
forecast period. Model guidance are suggesting easterly winds at
less than 18 knots and seas of 5 feet or less through much of the
forecast period.


SJU  80  92  80  88 /  20  40  40  40
STT  81  89  81  90 /  20  30  30  30




LONG TERM....Previous DIscussion
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