Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 270904

Area Forecast Discussion
National Weather Service San Juan PR
504 AM AST Tue Jun 27 2017

.SYNOPSIS...A Saharan air layer with extensive area of suspended
Saharan dust particulates will linger across the region through
at least Wednesday creating somewhat hazy conditions over the
land areas. A tropical wave will move across the region Thursday.


.SHORT TERM...Today through Thursday...A surface high pressure
across the central Atlantic and an upper low to the north
northeast of the local islands will dominate the weather pattern
today and Wednesday. A relatively dry airmass with a decent
concentration of Saharan Dust is expected today across the local
area, causing hazy skies and mainly fair weather for most of the
local area, especially in the morning hours. For the afternoon,
the upper trough to the north of the local islands may cause some
instability across the local area, which could cause showers and
thunderstorms to develop across the western sections of PR when
combined with the sea breeze convergence, diurnal heating, and
limited but available moisture. High resolution guidance insists
in afternoon showers and thunderstorms across western PR, although
some guidance suggests the activity across western PR and others
on SW-PR. Bottom line is that the highest chance of rain and
thunder will be in areas of sea breeze convergence across western
into southwestern PR.

Wednesday looks similar to today but the shower activity in the
afternoon should be a bit further north, for western and NW-PR. Then
on Thursday, a tropical wave is expected to move in with rather deep
moisture. This is expected to cause an increase in the shower and
thunderstorm activity coverage across the local forecast area.

.LONG TERM...Friday through Wednesday...Lingering moisture
associated with the tropical wave affecting us on Thursday will
maintain high chances for showers and thunderstorms across the
region Friday into Saturday. After the passage of the wave, a much
drier air, with some Saharan dust will encompass the region from
the east. Overall, seasonable weather conditions are expected in
the long term.


.AVIATION...VFR conditions will prevail across all TAF sites through
the next 24 hours across the local terminals, except maybe TJMZ
between 27/17Z and 27/21Z, where SHRA/TSRA could develop nearby and
cause TEMPO MVFR Conds. Otherwise fair wx is expected with light
VCSH across the area. Hazy skies are expected across the local area
but visibilities will remain P6SM. SFC winds will be mainly from the
east at 10 to 15KT with sea breeze variations developing by


.MARINE...Tranquil marine conditions are expected. Seas up to 5
feet and winds up to 15 knots are expected. Moderate risk of rip
current is expected in some beaches of northwestern Puerto Rico
and the south coast.


SJU  90  79  89  79 /  20  30  30  10
STT  91  80  90  80 /  20  30  30  20




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