Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 222017

Area Forecast Discussion
National Weather Service San Juan PR
417 PM AST Mon May 22 2017

.SYNOPSIS...High concentrations of suspended saharan dust particulates
continue to increase and will affect the region through Wednesday.
Lesser amounts expected to affect the area on Thursday and into the
weekend. The mid to upper level high pressure ridge will hold across
the region through Tuesday, with a weak short wave trough forecast
to quickly cross the region by Wednesday. Strong surface high across
the Atlantic will remain in place and continue to be the dominant
feature during most of the forecast period.


.SHORT TERM...Today through Wednesday...
Mostly hot and hazy weather conditions prevailed across the region
today. The high pressure ridge aloft and the lingering saharan air
layer limited convection across the region to maintain an overall
hot and dry environment. Satellite Imagery and the FAA terminal doppler
radar showed a few showers developing over parts of the west interior
sections of Puerto Rico, and only a few clouds were noted streaming
over the coastal waters and on the downwind side of the other islands.
Expect this activity to be of short duration with most of the cloudiness
and showers to diminish and dissipated after sunset. Overall fair skies
and hazy conditions will persist overnight with similar weather conditions
expected across the region through Wednesday. There is a change of a
few light showers to form and move across the coastal waters overnight
and during the early morning with limited or no significant rainfall
forecast over most of the islands each afternoon. The exception will
be over the west interior of Puerto Rico where daytime heating and
local forcing may lead to brief afternoon showers or possibly and isolated

The weak short wave is forecast to move rapidly through the area
on Wednesday, but lack of moisture transport and the lingering
dust should suppress and limit any significant convective development.
After the trough passage, Wednesday,upper level wind flow will
turn strongly northwest ahead of an approaching ridge which will
make overall conditions stable once again.

.LONG TERM...Thursday through Tuesday...
The mid to upper level ridge will strengthen once again across
the region and continue to dominate the Northeast Caribbean through
Friday. Surface high pressure will remain anchored across the central
and east Atlantic to maintain moderate easterly trade winds, which
will continue to bring a mostly dry and and stable air layer across
the region. Model guidance also continued to suggest that the Saharan
air layer will persist across the region through most of the period.
Therefore...conditions will remain hazy, relatively dry and stable
through Friday and into the weekend. It is not until the latter
part of the weekend through Monday of next week, when an induced
surface trough will bring moisture convergence across the region,
and increase the chance for showers and isolated thunderstorm
development across the portions of the islands and coastal waters.


.AVIATION...VFR prevailing. As heating mixes down drier air, the
only expectation for MVFR conds is under iso-sct SHRA/TSRA in wrn or
nwrn PR till 22/23Z / 23/02Z respectively. Visibilities will likely
remain less than 15 miles most areas due to Saharan dust. Sfc winds
ENE 5 to 15 kt with sea/land breeze influences. Maximum winds W 50
to 70 kts from FL380-500 thru 24/00z.


.MARINE...Marine conds are relatively tranquil, but will increase
in the western Caribbean and western Atlantic on Wednesday. Seas
still expected to near 7 feet by then.


SJU  79  90  80  90 /  20  20  20  20
STT  80  89  80  88 /  20  20  20  20




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