Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 210208 AAA

Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
1008 PM AST Fri Jul 20 2018

.UPDATE...Little change to forecast. Sounding shows good moisture
with 1.81 inches of precipitable water. This will allow a few more
showers than originally forecast and grids have been adjusted.


.AVIATION...A few SHRA will appear in ern PR with mtn tops
obscured til arnd 21/15Z. Otherwise VFR will prevail all TAF
sites. Winds East 5-15 kt incrg to 10-20 with gusts to 28kt aft
21/14Z. Max winds FL045 E 20 kt.


.MARINE...With winds 10 to 20 kt almost all waters seas will range
from 3 to 6 feet. At this time small craft advisories are not
anticipated next 7-10 days.


.PREV DISCUSSION... /issued 406 PM AST Fri Jul 20 2018/

A surface ridge of high pressure will continue to promote
easterly winds of 10 to 15 kts with higher gusts over the local
waters through Sunday. Dry stable air mass will continue to
suppress shower activity through Saturday. Saharan dust is
will remain anchored over the region thus affecting visibilities
through the weekend. A upper level low will retrograde to the
north of Puerto Rico late on Tuesday or early Wednesday this
accompanied by a tropical wave will help aid in the development of
showers and isolated thunderstorms.

SHORT TERM...Tonight through Monday
A dry stable air mass will continue to suppress shower activity
across Puerto Rico and the U.S. Virgin Islands through Saturday. A
plume of Saharan dust that moved off the African coast early this
week is currently maintaining it foot-hold over the region until
Sunday afternoon.

Sunday model guidance currently shows a well defined upper level
low to the north of Puerto Rico, and a pronounced jet streak
across the area. These features will increase instability and
upper level divergence over Puerto Rico. The aformentioned
features combining with the increase in low level moisture and
local and diurnal heating of the afternoon will increase rain
chances for portions of northern and western Puerto Rico on
Sunday afternoon.

Monday the jet streak becomes less pronounced but will remain
over Puerto Rico. Lingering moisture and local and diurnal effects
will help in the development of showers across portions of
western Puerto Rico.

LONG TERM...Tuesday through Sunday...
Tuesday expect showers across eastern Puerto during the morning
then showers will move into portions of western Puerto Rico during
the afternoon. Wednesday a vigorous tropical wave is expected to
move into the region as a result an increase in moisture will
cause showers and isolated thunderstorms over most of the region.
Wednesday the tropical wave moves west of the region as drier air
works in from the east. During the long term period tropical waves
and drier air masses will continue to move in and out of the
region through the long-term period.

AVIATION...VFR conds expected thru the forecast period. FEW SHRA
still possible over western PR later this afternoon. Saharan dust
will continue to reduce somewhat the VIS across the flight area,
however VIS should remain P6SM. Limited SHRA activity is expected
overnight. Surface winds will decrease to around 10 kt tonight into
Saturday morning.

MARINE...seas up to 6 feet with easterly winds of 10 to 15 kts
with higher gusts will prevail through the weekend. As a result
of seas reaching 6 feet small craft should exercise caution. A
low to moderate risk of rip currents exists for all the local


SJU  78  89  79  88 /  20  20  30  30
STT  79  89  78  89 /  10  10  30  30




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