Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 031526

Area Forecast Discussion
National Weather Service San Juan PR
1126 AM AST Mon Oct 3 2022


Issued at 1123 AM AST Mon Oct 3 2022

No significant changes to the forecast or reasoning. Heat index
values already reached or surpass 100 degrees Fahrenheit across
urban and coastal areas. A few showers are now moving across the
eastern portions of PR, while the rest of the islands have mostly
sunny skies. Moisture remains over the region, with the 12Z upper
air sounding showing precipitable water at 2.06 inches. The wind
flow over the region is relatively light out from the east-
Southeast. As such, showers are likely for the northwest and
interior portions of Puerto Rico and are expected to be generally
slow moving. Locally high rainfall totals are possible.


Issued at 1123 AM AST Mon Oct 3 2022

VFR conditions will prevail across all terminals through the
forecast period. SHRA/TSRA will developed over the interior and
NW-PR btwn 03/17-23z. This activity will required TEMPO MVFR conds
at TJBQ. VCTS remains possible at TJPS during this period. East
to southeast winds will continue at 8-12 kt, with sea breeze
variations aft 03/14z.


Issued at 1123 AM AST Mon Oct 3 2022

Winds are gentle to moderate out from the east to east-southeast.
Local buoys are indicating seas of 4 feet or less. Mariners should
exercise caution due to afternoon thunderstorm activity over the
northwest and west PR.


.SYNOPSIS...Unsettled weather conditions will continue throughout
the local area with very active afternoons accompanied by heavy
rainfall and thunderstorm. A tropical wave will cross the region
by Tuesday promoting unstable weather conditions. A slight patch
of drier air will arrive to the islands on Thursday, but then
after a wetter weather pattern will return.


.SHORT TERM...Today through Wednesday...

A TUTT-low will remain northeast of the region while a weak mid-to-
upper-level ridge builds over and west of the area through the short
term period. At the surface, a high pressure over the central
Atlantic will continue to promote light southeasterly trades today,
increasing between 10-15 kt and more easterly on Tuesday and
Wednesday. PWAT content is expected to remain at or above normal
values during the next few days. This available moisture will
combine with daytime heating and the sea breeze convergence,
resulting in shower and thunderstorm development each afternoon.
Today, mainly over central and west/northwest Puerto Rico and as
well over isolated areas of northern PR. In addition, a TUTT-induced
low-level trough is expected to cross the region between Tuesday and
Wednesday. This will further increase moisture content and enhance
early morning convection between the U.S. Virgin Islands and eastern
PR, followed by an increase in areal coverage of afternoon
convection across PR. Urban and small stream flooding can be
expected each day with the thunderstorms.

Maximum temperatures today are forecast to reach the low 90s across
urban areas of northern, western and southwestern PR. The heat index
could reach 108F between Arecibo and Dorado, where a Heat Advisory
is in effect from 1100 AM AST through 300 PM AST.


.LONG TERM...Thursday through Tuesday...

A Tropical Upper Tropospheric Trough (TUTT) located northeast of the
local islands will continue to interact with the available
moisture to support and enhance unstable weather conditions
across the local area. By Thursday, the latest models guidance
(GFS and ECMWF) shows a slightly drying weather pattern.
Nonetheless, the TUTT will continue to move towards the
northeastern Caribbean during this time. Expect active afternoons
with the potential for thunderstorms and heavy rain. With the
expected activity and saturated soils from the previous rains, the
threat for thunderstorms, urban and small stream flooding, even
mudslides will continue until the early next week. Precipitable
Water Content (PWAT) values will range between 1.70 to 2.10 inches
which indicate a moisture pattern that will continue across the
area, just ahead of a tropical wave on Monday. For Tuesday
onwards, the models are showing and interaction with the TUTT and
the tropical wave, the is a high uncertainty to determine the
impacts associated with these events but unstable weather
conditions will persist for the second half of the long-term.


.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals through the forecast period. However, SHRA/TSRA is
expected to develop btw 03/18-21z over the interior and
west/northwest PR, which may cause tempo MVFR conds at TJBQ. VCTS is
possible at TJPS during this period. East to southeast winds will
continue at 8-12 kt, with sea breeze variations aft 03/14z.


.MARINE...Mariners can expect gentle to moderate winds and seas
at 4 feet or below that will persist through at least today.
Showers and isolated thunderstorms are expected to develop every
afternoon this could result in gusty winds and locally
deteriorated conditions.


PR...Heat Advisory until 3 PM AST this afternoon for PRZ005.



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