Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 032004

Area Forecast Discussion
National Weather Service San Juan PR
404 PM AST Mon Aug 3 2020


A drier air mass will move into the region tonight and remain
through Wednesday. The drier air will limit the development of
afternoon showers in most areas however, diurnal and local
effects will cause some showers to develop mainly over parts of
the interior and west sections of Puerto Rico during the
afternoon. Thursday through the end of the work week moisture will
increase due to a TUTT induced weak perturbation on Thursday, and
a tropical wave which is forecast to move over the area on


.SHORT TERM...Rest of Today through Wednesday...

Showers with isolated thunderstorms will continue in northwestern
and north-central Puerto Rico for the next few hours, and settle
down by sunset. Thereafter drier air is expected to move in across
the region overnight.

Currently we have an upper level trough to the north-northwest, and
moving towards the west. This low is providing cooler air aloft
and aided in the development of showers and isolated thunderstorms
today. However, it is moving away quickly and will no longer be a
factor. High pressure will build in its place for tomorrow, along
with Saharan dust. Furthermore, well below average moisture
content will accompany the ridge and dust, resulting in
substantially calmer weather for the remainder of the short term

Thus for tomorrow, plenty of sunshine with haze is expected, though
it is still possible for showers to develop tomorrow afternoon over
western to northwestern Puerto Rico. These showers will likely not
be very impactful. The same story is expected for Wednesday, though
winds will be more out of the east rather than east-southeast. Thus
showers that develop in the afternoon will most likely favor western
Puerto Rico near Mayaguez. Again, these showers will likely be
shallow and unimpactful-impactful given the lack of moisture,
especially at mid- atmospheric levels. High pressure in the
central Atlantic will produce normal easterly winds of around 10
to 15 mph each day.

PREV DISCUSSION... /issued 451 AM AST Mon Aug 3 2020/

.LONG TERM...Thursday through Monday...

A retrogressing TUTT is forecast to move over the region by
Thursday, an induced low-level perturbation will increase the
potential for scattered showers and isolated thunderstorms over
the local waters and enhance afternoon convection over the
islands. A tropical wave will bring additional moisture content
and instability on Friday to cause another round of scattered
convection across the region. Therefore, afternoon showers and
thunderstorms each day over mainland PR will have the potential to
cause urban and small stream flooding. Another Saharan Air Layer
with drier air is forecast to move during the weekend promoting
overall fair weather conditions across the islands. Trade winds
will also increase during the weekend into next week, and any
shower that develops should move quickly and leave mostly minor
rainfall amounts.



Mainly VFR conditions expected to prevail during the forecast
period. In the afternoon, VIS could be reduced due to SHRA/TSRA
that could cause brief MVFR conditions over TJBQ/TJMZ. VCSH are
possible at TJSJ as well. SFC winds will remain from the east-
southeast at 5 to 10 knots overnight.



Seas will range from 3 to 5 feet across the nearshore and outer
waters through Friday. A moderate risk of rip currents for the
north facing beaches of Puerto Rico and the northeastern beaches
of Culebra and the U.S. Virgin Islands on Wednesday. Easterly winds
ranging from 5 to 15 kts will continue over the next several days.


SJU  91  79  92  79 /  50  50  30  20
STT  88  81  89  80 /  40  40  40  30




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