Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 241453

Area Forecast Discussion
National Weather Service San Juan PR
1053 AM AST Thu May 24 2018

.UPDATE...It looks like today will be very similar to yesterday in
terms of the weather observed. The morning weather has progressed
as expected with mostly fair weather across the local islands
with only isolated brief showers. The latest visible satellite
imagery is indicating that cloudiness is slowly developing across
the local islands. Some clouds are streaming off the USVI and some
cloudiness is also streaming off the Luquillo Mountain Range into
the San Juan Metro area. Some cloudiness is also developing across
the interior and western sections of PR. Most of the areas that
have cloudiness developing have a good chance of rain. However,
the areas with the highest chance of significant rainfall will be
the northwestern quadrant of PR and portions of the San Juan metro
area, some of these showers could cause urban and small stream


.AVIATION...VFR conds across the local terminals with SHRA/TSRA
developing across W-NW PR after 24/17Z which could cause MVFR
conds TJMZ and TJBQ. TJSJ could observe some SHRA but mainly in
the vicinity. Winds will continue from the east at 10-15KT with
occasional gusts and sea breeze variations through this afternoon.


.MARINE...Small craft operators are urged to exercise caution due
to seas up to 6 feet into tonight. Seas are expected to subside
slightly by Friday, with seas generally up to 5 feet. The coastal
winds will be mainly 10-20 knots for the rest of today. There is
a moderate risk of rip currents across many of the local beaches.


.PREV DISCUSSION... /issued 449 AM AST Thu May 24 2018/

SYNOPSIS...A short wave trough aloft is forecast to swing north of the
islands as a TUTT low moves northeastward from the Leeward
Islands the next few days. The islands will be wedge by a ridge
to the northwest and a TUTT low to the northeast through the
upcoming weekend. Tropical wave will approach the Lesser Islands
between Saturday night into Sunday morning.

SHORT TERM...Today through Saturday...

Not much change to the local weather pattern is expected for today
across the forecast area. Partly to variably cloudy skies with brief
passing shower activity are expected across eastern portions of
Puerto Rico and the USVI during the morning hours. During the
afternoon, heavy showers and possibly a few isolated thunderstorms
are expected to develop across the northwest quadrant of Puerto
Rico. Additional shower development is expected across the San Juan
metro area downwind from El Yunque as well as some possible
streamers developing downwind from the USVI. The rainfall expected
across the northwest quadrant of Puerto Rico as well as across the
San Juan metro area could result in ponding of water on roadways and
in poor drainage areas as well as some localized urban and small
stream flooding.

Model guidance continues to indicate an increase in low-level
moisture via a southeasterly wind flow for Friday and Saturday.
Therefore, continue to expect passing trade wind showers affecting
eastern portions of Puerto Rico and USVI during the morning hours
followed by heavy showers developing across the northwest quadrant
of Puerto Rico as well as across portions of the San Juan metro area
downwind from El Yunque during the afternoon hours. Given the recent
rainfall activity, the potential exists for urban and small stream
flooding where the heaviest rainfall occurs.

LONG TERM...Sunday through Friday...

An increase in low level moisture is expected by early next week
as a tropical wave combine with an upper level trough and plenty
of low level moisture at the surface. As a result, scattered to
numerous showers with isolated thunderstorms are expected to
affect the local area Sunday into Monday. Best activity is
expected to develop across the Cordillera Central of Puerto Rico.
A drier air mass is expected to encompass the region Tuesday and
Wednesday, followed by another tropical wave which is forecast by
SJU-GFS model to reach the northeast Caribbean by Thursday next

AVIATION...Mainly VFR conds expected across all terminals through
24/16Z. A few brief passing SHRA could affect the USVI and TJSJ
terminals during the morning hours. +SHRA and isolated TS
development expected across western and northwestern sections of PR
after 24/16Z. Therefore, MVFR conditions are expected across TJBQ
and TJMZ terminals. VCSH possible across TJSJ between 24/16-20Z.
Winds will be from the E-SE between 15-20 kts with sea breeze
variations and occasional gusts through 24/22Z. Winds expected to
diminish below 10kts after 24/23Z.

MARINE...Seas between 4 to 6 feet and winds up to 20 knots are
expected across the local waters. Small craft operators are urge
to exercise caution across most waters.


SJU  87  77  87  77 /  40  40  40  30
STT  87  77  87  77 /  30  30  30  30




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