733
FXCA62 TJSJ 142010
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
410 PM AST Fri Jun 14 2024

.SYNOPSIS...

An induced surface trough passing through the region will promote
passing showers and afternoon convection tonight through tomorrow,
however mid to upper- level ridging will limit widespread
rainfall. A plume of Saharan dust of moderare to high
concentration is forecast to spread across the region, causing hot
and hazy conditions that last through the second half of the
weekend into the next workweek. An Excessive Heat Watch is in
effect for tomorrow.

&&


.SHORT TERM...Tonight through Sunday...

A surface trough will exit the region overnight, heading
northwestward which will begin a veering of the surface to lower
level winds to a south-southeasterly direction by tomorrow lasting
through Sunday. Meanwhile, a mid to upper-level ridge continues to
anchor across the central Caribbean, providing overall stable
conditions. A dry airmass containing Saharan dust begins to move
northward across the eastern Caribbean basin late Saturday into
Sunday, however plenty of moisture hung up from the short wave
trough will sit over the area keeping rain possible in the forecast
through the weekend. Most of the expected rainfall will be across
eastern Puerto Rico through the day and night in the form of passing
showers, however during the afternoons convection is likely across
northern central to northwestern Puerto Rico with the southerly
component in the wind flow.

The combination of suspended Saharan dust particulates and the mid
to upper level ridging will favor subsidence and good compression of
the warm air in the low layers throughout this weekend. Daytime high
temperatures will be in the low 90s especially along the north and
west coastal areas with maximum heat indices expected to again
exceed 100 degrees, resulting in excessive heat impacts particularly
along the west north and east coastal and urban areas. Currently a
Heat Advisory is in effect for most of the islands tomorrow besides
the interior and southern coastline of Puerto Rico.

&&

.LONG TERM...Monday through Thursday...
/from previous discussion/

Although a decrease in saharan dust is forecast to start the
workweek, another pulse will continue to promote hazy conditions
through most of the long term period. Current model guidance
suggest Precipitable Water (PWAT) values at generally normal
values to start the period with a patch of below normal PWAT
values reaching the area on Tuesday. For Wednesday and Thursday,
columnar moisture will increase once again to normal to above
normal values as moisture related to a surface trough and a
possible wave, although uncertainty remains. A developing upper
level trough near the area will also increase instability. Although
model guidance suggest moisture over the mid levels, a more
notable increase is suggested by Wednesday. Most available
moisture to start the workweek will remain below 850 mb,
however. East to east- southeast surface winds should affect the
islands through Thursday, when they become more easterly and
increase. This will steer warmer tropical air towards the islands,
promoting overall warm to hot conditions. Heat related products
will possibly be issued for the islands to start the period. 925
mb temperatures are forecast to be above normal to start the
workweek.

&&

.AVIATION...
(18Z TAFS)

Scattered SHRA expected to prevail across eastern PR and TJBQ
through 22Z, with periods of reduced VIS and low ceilings possible.
Additional activity expected to increase after 22Z for the Caribbean
waters and USVI terminals as well. Winds are shifting from the ESE
at around 10-12 knots, becoming more from the south above the SFC to
FL050 on 15/12Z. Hz due to Saharan dust is expected to increase
after 12/16Z for the USVI, but VIS should remain at P6SM.


&&

.MARINE...
Surface high pressure over the Atlantic and an induced trough over the
area will promote light to moderate east to southeast winds.
Moist air will allow showers and isolated thunderstorms to develop
over portions of the local waters tonight through the weekend. Winds
will continue to diminish and veer, becoming more southeasterly
through the weekend with increasing Saharan dust expected across the
region through Sunday.



&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 6 PM AST this evening for PRZ001-005-008-010.

     Excessive Heat Watch from Saturday morning through Saturday
     afternoon for PRZ001-002-005-008-010-012-013.

VI...Excessive Heat Watch from Saturday morning through Saturday
     afternoon for VIZ001-002.

AM...None.

&&

$$

WS/YZR/RC