987
FXCA62 TJSJ 152112
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
512 PM AST Mon Jul 15 2024

.SYNOPSIS...

An upper level low and associated induced surface trough will
increase shower activity on Tuesday and Wednesday. A Saharan Air
Layer will move over the local area during the second part of the
week, promoting hazy skies. A tropical wave with good moisture
content is expected to reach the islands by Saturday. Breezy
conditions and east to southeast winds will return by midweek.


&&

.SHORT TERM...Monday through Wednesday...

Showers and thunderstorms developed over southwestern Puerto Rico
during the afternoon hours. The Doppler radar estimated between 1
and 2 inches of rain over San German and Hormigueros. Maximum
temperatures were from the upper 80s to mid 90s across coastal
areas to the mid 70s across the higher elevations. Winds were from
the east to northeast up to 15 mph with higher gusts at times.

A TUTT-low will linger north of the region through Tuesday and an
induced surface trough will cross the local area between Tuesday
and Wednesday from the east. This will promote shower and
thunderstorm development across the local waters and portions of
the islands each day. The precipitable water content is expected
to increase around 2.00 inches through this period, while the 500
mb temperature drops to -6C. Therefore, thunderstorms could lead
to periods of of heavy rainfall that will cause urban and small
stream flooding. Late Wednesday, a moderate to strong Saharan Air
Layer is expected to filter across the region, promoting hazy
skies into Thursday.


.LONG TERM...Thursday through Tuesday...From Prev Discussion...

Recent model guidance suggests a strong surface high pressure will
remain anchored across the Atlantic and north of the region to
maintain moderate to strong east southeast winds on Thursday. Winds
are then to become more east northeast by Friday into the following
weekend as a tropical wave will enter the eastern Caribbean and
cross the forecast area. This is expected to bring increasing
moisture and instability to the region along with a wind surge and
moderate to strong southeasterly winds by Saturday afternoon, as
the tropical wave crosses the region. Accompanying the wave and
thereafter another extensive plume of dense Saharan dust is forecast
to quickly spread across the region Sunday through Monday then
gradually diminish from Tuesday onwards. By then winds are to become
more easterly with yet another Tutt and induced surface trough
forecast to approaches from the east.

All in all the most impactful period will so far be late Thursday
through Saturday, when enhanced overnight and afternoon convection
is expected due to the tropical wave along with good moisture
convergence and cooler advective temperatures aloft. This will be
followed by hazy/dusty conditions and a somewhat drier airmass
due to the forecast dense Saharan dust particulates which will
maintain hot and humid conditions. Temperatures are expected to
continue slightly above normal and elevated to significant maximum
daytime heat indices are forecast to be reached at times in some
coastal and urban areas. Marine conditions area also expected to
deteriorate by Friday and into the weekend due to the tropical wave
and the increasing trade winds. Therefore precautionary statements
and small craft advisories may be required for all or portions of
the local waters and passages by that time.


&&

.AVIATION...
(18z TAFs)

VFR conds expected to continue for the next 18 hours except for some
dissipating SHRA activity in wrn interior PR. Sct SHRA and ovr El
Yunque aft 16/08Z. E flow 5-10 kt will bcm aft 16/14Z ESE 10-15 kts
with gusts to 23kt in sea breezes. Incrg SHRA ern PR.


&&

.MARINE...

Surface high pressure across the western Atlantic will promote
light east to northeast winds today, then become more southeasterly
and increase to moderate on Tuesday and become breezy by midweek
due to the arrival of a tropical wave and accompanying wind surge.
As the wind increases, choppy seas will be likely across the local
waters and passages, resulting in seas up to 7 feet and winds up
to 20 knots. Small craft advisories and precautionary statement
will be required by then.


&&

.BEACH FORECAST...

By Tuesday and for the remainder of the workweek, there will be a
moderate risk of rip current for most beaches and therefore life-
threatening rip currents will be possible in the surf zone.


&&

&&

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

$$

DSR/ERG/MMC