Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 212040

Area Forecast Discussion
National Weather Service San Juan PR
440 PM AST Tue May 21 2019

.SYNOPSIS...The chance for shower and thunderstorm activity will
continue to increase as a mid to upper level trough moves closer
to the forecast area. Although this feature is expected to weaken
by the end of the week, trofiness and plenty of moisture will
persist much of the upcoming week.


.SHORT TERM....Tonight thru Thu...

Heights will continue to fall as a mid to upper level trough
-now located in the vicinity of The Bahamas- shifts southeast;
reaching the northeast Caribbean by Thursday. This feature will
also induce a surface trough enhancing moisture advection across
the local islands with precipitable water near 2 inches by
Thursday morning.

Under plenty of moisture and favorable upper level conditions,
the chance for showers and thunderstorms will continue to increase
through the forecast period. Expect shower and thunderstorm
development across central and western Puerto Rico Wednesday
afternoon. The intensity and areal coverage of showers and
thunderstorms will increase on Thursday as the aformentioned
trough moves closer to the forecast area. The best chance for
shower and thunderstorm development across the USVI is on
Thursday, as well. As a result, there is an increasing potential
for urban and small streams flooding, particularly Thursday.

Meanwhile, shower activity over western areas of Puerto Rico will
diminish late this afternoon, leaving partly cloudy skies.
Passing showers will remain possible across the eastern third of
Puerto Rico and the outlying islands overnight.

.LONG TERM...Fri thru Tue /issued 504 AM AST Tue May 21 2019

A trof pattern will maintain unstable weather conditions across
the area throughout the week. Model guidance continues to suggest
precipitable water values ranging between 1.7 and 2.20 inches
through the long term period. Therefore, the combination of
abundant tropical moisture with good instability will result in
periods of enhanced shower and thunderstorm activity, especially
across along and north of the Cordillera Central of Puerto Rico
each afternoon. Showers and isolated thunderstorms should not be
ruled out across portions of eastern PR and the USVI, especially
during the overnight hours.

Global models continues to suggest an amplifying trough
interacting with deep tropical moisture early next week, between
Sunday or Monday. If these solutions are correct, unsettle weather
conditions could be expected the first part of the upcoming week.
In addition, a tropical wave will reach the local islands around
Wednesday of the upcoming week. At this time, confidence is low to
moderate because this solutions are to far in time. However,
please continue to monitor the latest forecast updates during the
next several days as the picture becomes clearer.


.AVIATION...SHRA/TSRA across NW-PR to continue through 20/22Z,
possibly causing TEMPO MVFR conds at TJBQ/TJMZ. -SHRA at TJSJ
through 21/18Z. The rest of the local terminals will observe VFR
conds. After 21/23Z, all of the local terminals are expected to
observe VFR conds, with only brief VCSH possible at TIST and TISX
during the overnight hours. Local winds from the ESE at 10-15KT
expected through 21/23Z with sea breeze variations and occasional
gusts, gradually decreasing thereafter through the night.


.MARINE...Seas below 5 feet and winds 15 to 20 knots to continue
during the forecast period. Along the coastal areas, a low to
moderate risk of rip currents is expected to continue through
much of the week. Criteria for SCAs are not expected to be


SJU  79  90  76  87 /  20  40  40  70
STT  78  86  76  86 /  30  50  50  40



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