375
FXCA62 TJSJ 121524
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1124 AM AST Mon Aug 12 2024

.UPDATE...
Potential Tropical Cyclone continues to approach the region, and a
Tropical Storm Warning is now in effect for Puerto Rico and the
Virgin Islands. The track was shifted westward, and now shows the
future tropical storm making landfall over eastern Puerto Rico.
However, the main threat continues to be the flooding rains
anticipated to begin on late Tuesday and stretch into early
Thursday. Strong gusty winds are also anticipated for the Virgin
Islands, Vieques, Culebra and portions of eastern and central
Puerto Rico. Hazardous marine and coastal conditions are also
expected, beginning late Tuesday.


&&

.PREV DISCUSSION... /issued 536 AM AST Mon Aug 12 2024/

SYNOPSIS...

Above normal moisture levels, the proximity of an upper-level
trough, and local effects will result in overnight and early
morning passing showers followed by afternoon showers with
thunderstorm activity, mainly across the interior and western
Puerto Rico through Tuesday. Then, the forecast for the rest of
the week will be dominated by the Potential Tropical Cyclone Five.
The system is expected to become a tropical depression later
today or tonight. Under the current forecast track, the closest
approach of this system will near (or over) the northern USVI
early Wednesday morning. A Tropical Storm Watch and a Flash Flood
Watch are now in effect for Puerto Rico and the U.S. Virgin
Islands. The main threats associated with this system are flooding
rains, landslides, windy or possible tropical storm conditions
and hazardous coastal and marine conditions.

SHORT TERM...Today through Wednesday...

A Tropical Storm Watch has been issued for the U.S. Virgin Islands
with additional watches to be required later today. The Potential
Tropical Cyclone Five will bring tropical storm force winds and
periods of heavy rain, with the potential for flash flooding and
mudslides. Hazardous marine and coastal conditions are also
expected, beginning as early as Tuesday Evening. First rainbands are
so far forecast to arrive by Tuesday afternoon, becoming more
frequent and heavier by Tuesday Evening and continuing through
Wednesday morning.

At 200 AM AST (0600 UTC), the disturbance was centered near latitude
14.3 North, Longitude 51.4 West. The system is moving toward the
west-northwest near 23 mph (37 km/h)  and this motion is expected to
continue during the next couple of days.  On the forecast track, the
disturbance is expected to move across portions of the Leeward
Islands on Tuesday and approach the U.S. and British Virgin Islands
Tuesday evening.

Recent satellite imagery as well as satellite derived precipitable
water products and model guidance, all suggest a slight decrease in
columnar moisture today in advance of the broad and elongated
Potential Tropical Cyclone Five. This disturbance was now some 715
miles east southeast of the island of Antigua quickly moving west
northwest.

Presently the proximity of a TUTT lifting north of the region and a
building upper high pressure east of the area,  will aid in
promoting overnight and early morning showers across portions of the
north and east sectors of the islands, as winds become more east
northeast. Local sea breeze convergence, diurnal heating, local
orographic effects, will therefore promote afternoon showers and
possibly isolated thunderstorms, particularly across the interior
and west to southwest sections of Puerto Rico. For the U.S. Virgin
Islands, mainly passing showers driven by the wind flow are expect
to continue with some reaching some of the islands at times.

By Tuesday through Wednesday, with the increasing northeast winds,
expect more frequent passing showers during the overnight and
morning hours with also increased potential for more widespread
afternoon and evening showers and thunderstorms with the approach of
the aforementioned tropical Potential tropical cyclone Five. Current
model guidance and the current NHC forecast track has PWAT values
rapidly increasing late Tuesday through the rest of the period, as
the disturbance and its associated outer bands approach and increase
in frequency across the easternmost section of Puerto Rico as well
as the U.S. Virgin Islands by the end of the period. By then the
potential for excessive rainfall and flooding rains will increase as
well as rapid rises along rivers and streams and potential for
mudslides and rockfall in higher elevations of Puerto Rico. Tropical
force winds and/or wind gusts will also be likely during the latter
part of the period for most of the forecast area. s

Residents and visitors should continue to monitor the progress of
this system and review their tropical emergency plans.Please refer
to the latest Tropical Cyclone Bulletin (TCPAT5) issued by National
Hurricane Center and Hurricane Local Statements (HLSSJU) issued by
WFO San Juan PR for the most up to date information.

LONG TERM...Thursday through Sunday...

For the beginning of the long-term forecast, hazards will continue
to depend on the potential impacts from the now Potential Tropical
Cyclone Five, which is forecast to move west-northwestward across
or near the region as a tropical storm. The main threats
associated with this system are flooding rains, landslides, windy
or possible tropical storm conditions and hazardous coastal and
marine conditions. PTC Five should start to move away from the
area on Thursday generating southerly winds. Residual moisture
will continue to be driven by the wind flow into our region
causing additional rain. Heavy rainfall may result in locally
considerable flash flooding and mudslides in portions of the U.S.
Virgin Islands Tuesday and Wednesday, and into Puerto Rico
Wednesday through early Thursday. Weather conditions are expected
to quickly improve at the end of the week as a drier-than-normal
air mass, with pockets of low-level moisture, moves into the area
and we switch to a more typical pattern.

AVIATION...

(06Z TAFS)

Prevailing VFR conds during prd but with passing SHRA/Isold TSRA  to
continue over the regional waters and en route btw islands. Low
level winds continue from the east and is expected to become more
east northeast then northeasterly by end of period as winds increase
due to the approaching of the Potential Tropical Cyclone Five. Sfc wnds
calm to light and variable but becoming east to northeast 10 to 15
mph with ocnly hir gust up to 25 kts psbl. Passing shra may cause
local mtn top obscurations over interior sections of PR and brief
MVFR conds. Aftn SHRA/TSRA expected over central and west sections
of PR 12/16Z with mostly Isold SHRA at the USVI terminals.

MARINE...

A surface high pressure across the North Atlantic will maintain
moderate to locally fresh easterly winds, creating localized choppy
conditions for small craft. Potential Tropical Cyclone Five,
located 940 miles ESE of San Juan, is expected to move into the
local waters by Tuesday evening into Wednesday as a tropical
cyclone. However, marine conditions in our eastern Atlantic waters
and the Anegada Passage could deteriorate as early as Tuesday
morning. Further deterioration in marine and weather conditions is
expected Wednesday through Thursday.

BEACH FORECAST...

Today, there is a moderate risk of rip currents across most
beaches of Puerto Rico, Vieques, Culebra, and the U.S. Virgin
Islands. Similar conditions are anticipated tomorrow throughout
the day, then marine and coastal conditions will start to
deteriorate due to the approaching Potential Tropical Cyclone 5.
As a result, high risk of rip currents could start tomorrow night.
Please refer to the Surf Zone Forecast (SRFSJU) for more details
about the forecast.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Tropical Storm Warning for PRZ001>013.

     Flood Watch from Tuesday evening through Thursday morning for
     PRZ001>013.

VI...Tropical Storm Warning for VIZ001-002.

     Flood Watch from Tuesday evening through Thursday morning for
     VIZ001-002.

AM...Tropical Storm Warning for AMZ711-712-716-723-726-733-735-741-
     742-745.

&&

$$

AVIATION...CVB
IDSS...LIS
UPPER AIR...RC
HLS...ERG