623
FXCA62 TJSJ 022041
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
441 PM AST Thu May 2 2024

.SYNOPSIS...

A wet pattern is expected for this afternoon into Sunday as the
arrival of a mid to upper level trough. According to the GOES
satellite Imagery, there is a surface trough just north of the
region, resulting in showers, thunderstorms and cloudiness. A
Flash flood watch is in effect from Friday 6 AM AST to Sunday 6 PM
AST. An improve in marine conditions is forecast for tomorrow.

&&

.SHORT TERM...Tonight through Saturday...

A variable weather pattern prevailed during the morning and early
afternoon hours. Some showers affected northeastern sections of
Puerto Rico in the early morning hours. After that, shower
developed over the northwestern sections. Strong thunderstorms
affected regions of the offshore and nearshore Atlantic waters,
therefore, several Marine weather statements ans a special marine
warning were issued. Daytime temperatures fluctuated in the mid
80s to lower 90s across the coastal areas and in the upper 70s to
the lower 80s in the mountains.

A wet and unstable pattern is expected to continue as an upper-level
trough approaches the area from the west. This is allowing an
induced surface trough to develop north of the region and for
tropical moisture from the caribbean to move into the area,
increasing the chances for widespread rainfall and flooding
through this weekend. Friday into Saturday continue to appear to
be the most active days, with showers and thunderstorms being the
dominating features, particularly along the eastern half of Puerto
Rico and the U.S. Virgin Islands. An upper-level maxima will move
across the islands with winds around 80 knots on Friday, and
similar speeds will linger through the rest of the weekend.

Due to these conditions, a Flood Watch is in effect from Friday
morning through Sunday afternoon. Rainfall accumulations are
expected to range from 2 to 4 inches, especially for the eastern
half of Puerto Rico and the Virgin Islands with isolated higher
amounts possible between 6 and 8 inches. Elsewhere, 1 to 3 inches
are expected. Due to already saturated soils, any prolonged period
of heavy rainfall will result in urban and small stream flooding.
Some rivers will likely overflow their banks. Therefore, Isolated
life threatening flash flooding and mudslides are possible as well.
Please view the FFASJU product for more information.

.LONG TERM...Sunday through Thursday...

Update: A Flash flood watch will be in effect for Sunday until 6
PM AST for Puerto Rico and the U.S. Virgin Islands.

Lingering moisture and the departing upper level-trough will continue
to promote shower and thunderstorm development on Sunday. At
lower-levels, a surface high pressure is expected to build over
the western Atlantic during the first part of the week. This will
promote moderate winds from the east to northeast through the long
term period. In addition, the remnants of the previous surface
trough to our north or just across the northeastern Caribbean are
expected to merge with a frontal boundary across the central
Atlantic and linger over the local area through at least Thursday.
Also, at upper levels, another trough will pass mainly to our
north from Tuesday onwards, maintaining unstable conditions in
general across the region. The highest precipitable water (PWAT)
values are expected during this period, with global guidance
suggesting between 2.10-2.25 inches of PWAT from Monday morning
through Thursday afternoon. Therefore, any period of moderate to
heavy showers across the islands would lead to quick urban and
river flooding, as well as mudslides in areas of steep terrain.
Residents and visitors are encourage to monitor the evolution of
the weather conditions during the next 5 to 7 days, and stay alert
for the issuance of any possible flood watch/warning products.

&&

.AVIATION...
(18Z)
VRB weather conditions will persist through the period. SHRA and
possible VCTS are still forecast for the terminals through at least
03/02Z, particularly for TJBQ currently as a line of thunderstorms
extend form its VCTY to the offshore Atlantic waters. SHRA and TSRA
can result in brief MVFR conditions. ESE winds up to 15 kts through
03/00Z, with higher gusts near strong SHRA/TSRA, then increasing
after 03/12Z.

&&

.MARINE...

A surface high pressure extending from the western to central
Atlantic will promote light to moderate trade winds across the
regional waters. Seas up to 6 feet are expected across the Atlantic
waters today due to a subsiding northeasterly swell and the moderate
trades. An induced surface trough to our north will yield lighter
east to east-southeast winds and promote shower and thunderstorm
development across the area through early next week. Another weak
northeasterly swell is forecast to arrive across the local area,
resulting in building seas again.

&&

.HYDROLOGY...

A Flood Watch is in effect for for Puerto Rico and the U.S.
Virgin Islands from Friday morning through Sunday afternoon. For
more details please refer to FFASJU & FFASPN. Unstable conditions
(due to an upper- level trough approaching the area from the west
and an induced surface trough), increasing moisture, and lighter
winds will promote periods of showers and thunderstorms across the
local islands. Rainfall accumulations are expected to range from
2 to 4 inches, especially for the eastern half of Puerto Rico and
the U.S. Virgin Islands with isolated higher amounts possible
between 6 and 8 inches. Elsewhere, 1 to 3 inches are expected.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for PRZ001-002-
     005-008-012.

     Flood Watch from Friday morning through Sunday afternoon for
     PRZ001>013.

VI...Flood Watch from Friday morning through Sunday afternoon for
     VIZ001-002.

AM...None.
&&

$$

SHORT TERM...RC/LIS
AVIATION...MRR
MARINE...LIS