Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 270041
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
841 PM AST Mon Jun 26 2017

.UPDATE...The lingering moisture left behind the tropical wave,
now south of Hispaniola in combination with diurnal heating and
local effects produced scattered showers during the afternoon
hours across northwestern sections of Puerto Rico. However, this
activity dissipates rapidly after sunset. Not significant
precipitation was observed elsewhere over land areas.

The tropical wave across the Caribbean waters, south of
Hispaniola will continue to move westward well away of the region
tonight and Tuesday. For the overnight hours and Tuesday morning,
an overall dry and stable airmass with Saharan dust will prevail
across the region. As a result, mostly fair weather and hazy skies
will continue across the region with limited shower activity
expected. However, isolated to Scattered showers should be focused
mainly over the west interior sections of Puerto Rico tomorrow
afternoon. Similar conditions are expected for Wednesday. A tropical
wave is expected to reach the eastern Caribbean on Wednesday
passing mostly south of the local islands Thursday and Friday. An
increase in cloudiness, showers and possible thunderstorms are
expected in association with this wave.

&&

.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 27/22Z 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 27/14Z.

&&

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

&&

.PREV DISCUSSION... /issued 451 PM AST Mon Jun 26 2017/

SYNOPSIS...Overall dry and stable air mass prevailed across the
region today, as the tropical wave that affected the forecast area
overnight and early this morning, quickly exited the region and
entered the Central Caribbean during the afternoon. A Saharan air
layer with extensive area of suspended Saharan dust particulates
quickly followed and will linger across the region through at least
Tuesday creating somewhat hazy conditions over the land areas.

SHORT TERM...Rest of today through Wednesday...

Diurnally induced shower activity will diminish by sunset leaving
partly cloudy to mostly clear skies. For the overnight hours and
on Tuesday, A overall dry and stable airmass with Saharan dust
will linger across the region. As a result, mostly fair weather
skies but somewhat hazy conditions, can be expected with limited
shower activity. Isolated to Scattered showers should be focused
mainly over the west interior sections of Puerto Rico. Similar
conditions expected for Wednesday, however a quick surge of
moisture in the easterly trade winds will bring early morning
showers mainly to the windward side of the islands. This will be
followed by locally induced afternoon showers mainly over the west
and southwest sections of PR as winds are to become more east
northeast.

LONG TERM...Thursday through Tuesday...

Next tropical wave/easterly disturbance is still forecast to enter
and move across the eastern Caribbean Thursday through Friday where
it is then expected to merge with a broad surface trough forecast to
develop and spread across the central and eastern Caribbean. This overall
pattern should increase low level moisture and layered
precipitable water content across the region during the latter
part of the work week and into the upcoming weekend. Recent model
guidance continued to suggest increasing Pwat values to near two
inches as moisture is expected to converge and pool across the
east and northeast Caribbean. In addition the proximity of the
upper level Tutt should also bring favorable conditions aloft to
allow for more frequent early morning showers and afternoon
convection across the islands and coastal waters through at least
Saturday. A gradual decrease in moisture and improving conditions
aloft is so far forecast for Sunday and into the early part of the
following week.

AVIATION...VFR conditions will prevail across all TAF sites durg
prd. Brief MVFR conds psbl ovr W PR and vcty TJMZ and TJBQ til from
26/22Z in SHRA/ isold TSRA. Haze ALQDS across local flying area due
to suspended Saharan dust spread across the region thru Tuesday.
However vsby P6SM expected durg prd at all terminals. Low level winds
fm E-SE 15-20 kts blo FL200. Except for local sea breeze variations...Sfc
wnd E-SE around 15 kts with ocnl higher gusts. No sig operational
wx impacts attm.

MARINE... Mariners can expect seas of 3-5 ft and winds of 10-20 kts
across most waters. Locally fresh winds may create choppy seas along
the coastal waters north and south Puerto Rico between 15Z- 21Z
each day.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  79  90  78  89 /  10  20  30  30
STT  79  90  78  90 /  20  20  30  30

&&

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

$$

SHORT TERM...JF
LONG TERM....RAM



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