Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 240815

Area Forecast Discussion
National Weather Service San Juan PR
415 AM AST Tue Oct 24 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 Wednesday. A mid to upper level trough will continue
to sink southwards across the eastern Caribbean with a cutoff low
expected to form in the southeastern Caribbean by Wednesday. An
induced low to mid level trough will develop and spread northwards
across the region during the weekend.


.SHORT TERM...Today through Thursday...
Low level moisture across the region are expected to steadily
increase today and during the next few days. The strong morning
insolation will aid to induce an unstable afternoon atmosphere for
the development of thunderstorms today through Thursday. However,
afternoon convection is expected to die shortly after sunset each
day. The northerly upper level jet over the region associated
with the upper level trough just north and across the eastern
Caribbean will also increase ventilation where convergence/divergence
remains neutral. The upper trough/low is expected to sink southeast
into the Lesser Antilles 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...Friday through Wednesday...
An upper level ridge will extend eastward across the local area
through Friday but will erode over the weekend, as a Tutt low
will shift westward across the southeastern Caribbean. An
increase in low to mid level moisture is expected by Saturday and
through the weekend, as an induced low to mid level trough moves
across the region. Increasing moisture and instability aloft will
favor better chance for increase showers and thunderstorm activity
across the islands and coastal waters through Sunday. A gradual
improvement and return to a more seasonal weather pattern is
so far forecast by Monday through Wednesday.


.AVIATION...Mostly VFR condition expected across the local flying
area throughout the forecast period. Only vicinity SHRA are possible
over the Leeward, USVI and eastern PR TAF sites sites until 25/15Z.
After 25/17Z...TSRA over western PR will bring MVFR or even IFR
conditions lower CIGS/VSBYS and mountain obscurations across TJMZ
and TJBQ. Latest TJSJ sounding indicated an easterly wind flow up 15
knots from the surface to around 12k feet, becoming west northwest
and stronger aloft.


.MARINE...Seas up to 5 feet offshore and between 1 to 4 feet near
shore. Winds of 10 to 15 knots are expected across the coastal waters.


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




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