224
FXCA62 TJSJ 112218
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
618 PM AST Sun Aug 11 2024

.SYNOPSIS...

Invest 98L has now been designated Potential Tropical Cyclone
Five. Under the current forecast track the closest approach of
this system will near (or over) the northern USVI early Wednesday
morning. The main threats associated with this system as it moves
through late Tuesday into Wednesday are flooding rains,
landslides, windy or possible tropical storm conditions and
hazardous coastal and marine conditions. Tropical Cyclone Watches
maybe required later tonight or early tomorrow.

&&

.SHORT TERM...Tonight through Tuesday...

Southeasterly steering flow, helped steer shower activity across
most of Puerto Rico, with lines of showers developing northwest of
the USVI, El Yunque and the central mountain range during the late
morning to afternoon hours. THe strongest activity with
thunderstorms converged over interior to northwestern PR, and
prompted the issuance of a Special Weather Statement and a Flood
Advisory over northwestern municipalities. Another flood product
was issued for several metropolitan area municipalities due to the
line from El Yunque. This shower activity at least brought some
relief in terms of heat to the northwestern quadrant. Official and
unofficial stations in St. Croix, north-central PR and
southwestern PR reported heat indices above 108 at around 14:30
AST. Radar estimated accumulations around/above 2 inches were
observed at Jayuya, Moca, Aguada, Naguabo and San Juan. San Juan,
particularly Santurce, saw radar estimated accumulations of up to
around 4 inches. Westernmost St. Thomas saw radar estimated
accumulations of up to 0.16 in, the most in the USVI.

Current satellite derived precipitable water (PWAT) values indicate
around high end normal to above normal (above 2.0 inches) values
across most of the values. The USVI had around 1.88 inches of PWAT
values. Columnar moisture is forecast to slightly decrease to normal
values tomorrow, Monday. A TUTT near the area will promote
increased night showers tonight across windward sectors of the
islands as winds become more easterly. Sea breeze convergence,
diurnal heating, local orographic effects, and the aforementioned
features will promote afternoon activity on Monday. Afternoon
showers and isolated thunderstorm activity are expected across the
interior and western Puerto Rico. For the U.S. Virgin Islands,
mainly passing showers driven by the wind flow will reach the area
at times through early Tuesday. Through Tuesday afternoon, a
similar pattern will persist with high heat indices and afternoon
showers and thunderstorms concentrating over western Puerto Rico.
Current model guidance and the current NHC forecast track has PWAT
values rapidly increasing late Tuesday to end the forecast period
as the now Potential Tropical Cyclone Five and possible outer bands
approach the easternmost region to end the period. Residents and
visitors should continue to monitor the progress of this system
and review their tropical emergency plans.


.LONG TERM...Wednesday through Saturday...

Long-term forecast hazards will 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
cyclone Tuesday night into Wednesday. A tropical cyclone watch or
warning has not been issued at the time of this product for Puerto
Rico and the USVI, as it is still early. However, we may need to
issue a watch later tonight or early tomorrow. However, given the
latest forecast track and intensity, now is an opportune moment to
initiate preparatory measures for a potential direct or indirect
impact from this system. The main threats associated with this
system are flooding rains, landslides, windy or possible tropical
storm conditions and hazardous coastal and marine conditions.
Under the current forecast track the closest approach of this
system will near (or over) the northern USVI early Wednesday
morning. Weather conditions are expected to improve quickly later
in the week as a drier-than- normal air mass, with pockets of low-
level moisture, moves into the area.

&&

.AVIATION...

(18Z TAFS)

Flow is now east southeast at 10 to 16 knots. Current SHRA/TSRA will
diminish ovr PR aft 11/22Z, and winds will diminish to 5-10 kt, but
SHRA activity ovr the local waters, arnd the USVI, and the SE third
of PR will cont thru the pd, with lcl mtn obscurations and MVFR
conds. Outlook: SHRA/TSRA to redevelop aft 12/15Z ovr PR.

&&

.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 950 miles ESE of Antigua is expected to move into the
local waters Tuesday afternoon and 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
are expected Wednesday and Thursday.

&&

.BEACH FORECAST...

Tonight, there is a moderate risk of rip currents on beaches of
northern, southeastern and southwestern Puerto Rico and Saint
Croix, extending to Culebra and Vieques tomorrow. Overall, the
risk of rip currents could start to increase to high starting
tomorrow night. Please refer to the Surf Zone Forecast (SRFSJU)
for more information.

&&

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

&&

$$

CAM/MRR/GRS/WS/ERF/EM