Area Forecast Discussion
Issued by NWS San Juan, PR

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263
FXCA62 TJSJ 280124
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
924 PM AST Tue Jun 27 2017

.UPDATE...Isolated passing showers will continue to affect the
eastern portions of Puerto Rico and adjacent islands. These
showers will continue to affect these areas through at least mid
morning. Showers and thunderstorms are possible across the western
sections in the afternoon hours.

&&

.AVIATION...Mostly VFR conditions will prevail across the local
flying area overnight. Brief MVFR conditions are possible over W
PR and vcty TJMZ and TJBQ til from 28/22Z in SHRA and possible
isolated TSRA. Haze ALQDS across local flying area due to
suspended Saharan dust spread across the region thru at least
wednesday. Low level E-SE winds up to 10 knots expected tonight,
increasing to 15-20 knots after 28/14Z.

&&

.MARINE...Mariners can expect seas of 3-5 ft and winds up to 20
kts across the coastal waters.

&&

.PREV DISCUSSION... /issued 421 PM AST Tue Jun 27 2017/

SYNOPSIS...High pressure ridge will remain the dominant feature across
the northeastern Caribbean through at least Wednesday. This will therfore
maintain a fairly strong cap inversion and as a result limit moisture
advection and convective activity across the forecast area. In addition
the extensive Saharan air layer continued across the region with high
amounts of suspended dust particulates spread across the region. This
lead to mostly fair weather but hazy conditions across most of the
islands.

SHORT TERM...Today through Thursday...

Local and diurnal effects lead to the formation of a few showers mainly
along the southwest and west interior sections of Puerto Rico, as well
as on the west end and downwind of the some of the of the islands. This
activity should quickly diminish around sunset leaving mostly clear
to partly cloudy skies overnight.

Similar conditions expected for Wednesday, but expect passing early
morning showers of short duration over the coastal waters and mainly
on the windward side of the islands. This will be followed by diurnally
induced showers over portions of the interior and west sections of
Puerto Rico. By Thursday, the mid to upper level ridge should slightly
erode overhead leading to a weakening of the cap inversion. A tropical
wave will enter and move across the the eastern Caribbean. This overall
pattern will result in an increase in layered moisture and low level
convergence across the forecast area. Therefore the expected surge
of tropical moisture along with good ventilation aloft will enhance
shower and thunderstorm development across the islands and coastal
waters through Thursday. Minor urban and small stream flooding will
therefore be likely in some areas.

LONG TERM...Friday through Wednesday...

Friday through at least Saturday, moisture trailing the wave in
the prevailing east to southeast wind flow should maintain high
chances for showers and isolated thunderstorm activity across the
region each day. Some of the activity may be briefly enhanced especially
during the afternoon hours, and once again lead to minor urban and
small stream flooding in isolated areas. By Sunday and into early
next week expect a return of more seasonal weather pattern with
passing trade winds showers followed by diurnally induced afternoon
convection mainly over the west sections of Puerto Rico.

AVIATION...VFR conds expected at all TAF sites except TJMZ where
brief MVFR conds are possible thru 21Z with SHRA/ISOLD TSRA.
Suspended saharan dust particles will continue to create hazy skies
across the flying area but visibilities are expected to remain P6SM.
Easterly winds of 15-20 kts will prevail below FL150.

MARINE...Typical marine conditions will prevail through at least
midweek. Mariners can expect seas of 3-5 ft and winds of 10-20 kts
across most waters. Locally fresh winds may along the coastal waters
north and south Puerto Rico may create create choppy seas through
21Z each day. A tropical wave forecast to move across the region
on Thursday should bring an increase in showers and thunderstorms
as well as winds and seas particularly across the local passages
and Caribbean waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  79  89  79  89 /  30  30  10  30
STT  80  90  80  89 /  30  30  30  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...EM
LONG TERM....RAM



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