494
FXCA62 TJSJ 090855
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
455 AM AST Fri May 9 2025

.KEY MESSAGES...

* Showers will continue to filter across eastern Puerto Rico and
  the U.S. Virging Islands through the morning hours today.

* Like previous days, afternoon showers and isolated
  thunderstorms are expected each day and could generate localized
  flooding impacts, including landslides in areas of steep
  terrain, particularly in vulnerable areas with saturated soils.

* Strengthening winds over the weekend into early next week will
  elevate the risk of life-threatening rip currents for beachgoers
  and create rough seas for small craft.

&&

.SHORT TERM...Today through Sunday...

A variable weather pattern prevailed during the night hours, where
shower activity was observed throughout northeastern Puerto Rici.
Most of the showers were observed first along Dorado and the
vicinity around Rio Grande and Loiza. Rainfall accumulations were
one to two inches in some areas. Overnight temperatures remained in
the lower 80s around the coastal areas and even more fresh across
the interior sections.

A stable and generally dry weather pattern will persist across
Puerto Rico and the U.S. Virgin Islands through at least today,
primarily due to the presence of a mid-to upper-level ridge
extending over the northeastern Caribbean. This ridge promotes
atmospheric subsidence, suppressing vertical motion and deep
convective development. Model guidance indicates that lapse rates in
the mid-levels, between 700 and 500 millibars, range from 5.0 to 5.5
degrees Celsius per kilometer,allowing a more stable pattern.
Additionally, temperatures at 500 millibars remain cool, near minus
7 degrees Celsius, but not cold enough to generate significant
widespread thunderstorms activity. Moisture content remains limited,
with PWAT values fluctuating between 1.70 and 1.75 inches, which
aligns closely with climatological normals. These conditions will
continue to support mostly stable weather, with only isolated to
scattered afternoon showers developing across interior and western
Puerto Rico due to local sea breeze convergence and orographic
effects. Thunderstorm activity is expected to remain limited because
of the weak instability and capping aloft. Across the U.S. Virgin
Islands, stable and dry conditions will dominate, with only a few
brief and shallow showers possible in the early morning hours.

By Saturday into Sunday, conditions turn more stable, as shown by
the 250 MB with the presence of a mid to upper-level ridge. This
feature will provide stable and drier conditions aloft and warmer
temperatures at 500 MB, rounding from -7 to -6 Celsius degrees.
Although upper-level conditions will significantly improve, PWAT
water values will rise slightly from 1.70 to 1.90 inches. The
available moisture will support more favorable conditions for
afternoon shower development. Although this increase in moisture may
lead to more frequent afternoon showers, particularly across the
northwestern and interior portions of Puerto Rico, the lack of
significant instability aloft will limit the intensity and vertical
growth of any convection. Rainfall accumulations are expected to be
light to moderate at most. The U.S. Virgin Islands may experience a
slight increase in early morning or overnight showers, but no major
rainfall or thunderstorm activity is anticipated. Overall,
conditions will trend toward slightly wetter afternoons while still
being influenced by stable upper-level conditions.


.LONG TERM...Monday through Friday...

The long-term period begins with a strengthening surface high over
the central Atlantic, which will tighten the local pressure
gradient and lead to increasing trade winds from Monday through at
least Wednesday. At the same time, precipitable water values are
expected to remain near seasonal normals (around 1.6 to 1.8
inches), supporting typical afternoon shower and thunderstorm
development across the interior and western sections of Puerto
Rico. Eastern Puerto Rico and the US Virgin Islands will likely
experience brief, trade wind-driven showers during the late night
and early morning hours.

During the second half of the workweek, a developing low-pressure system
over the western Atlantic will introduce changes to the overall
pattern. As it deepens and moves eastward, it will increase
moisture transport into the region while weakening the trade wind
inversion and enhancing upper-level support. PWAT values could
rise above 1.8 inches, allowing a more humid and unstable
environment. This evolving setup will favor more widespread and
intense convection Thursday and Friday, with showers becoming
deeper and more persistent. We encourage people to stay informed
with the latest updates.

&&

.AVIATION...
(06Z)

VCSH to SHRA will persist along TJSJ, TIST until 09/15Z.
Winds will continue VRB peaking up at 09/15Z from the E at 15
knots with gusty winds near the showers. SHRA/TSRA will start at
around 09/18Z across mountains, inducing lower ceilings and a
reduction in VIS. VCSH/SRHA will affect TJBQ at 09/18Z.

&&

.MARINE...

A broad surface high pressure extending into the Central Atlantic,
in combination with an induced surface trough northeast of the
region, will result in light to gentle flow through the end of the
workweek. Winds will increase by the end of the weekend as the
surface high pressure builds across the Atlantic. Mariners can expect
seas between 2 to 4 feet, occasionally 5 feet, for the next several
days. Occasional thunderstorms are likely across the regional waters,
especially in the afternoon, resulting in dangerous conditions for
mariners.

&&

.BEACH FORECAST...

Beachgoers can expect a moderate risk of rip currents along the
northwestern coastal areas of Puerto Rico, while the rest of the
local beaches should experience a low risk throughout the
workweek. However, life- threatening rip currents often occur near
groins, jetties, reefs, and piers.

&&

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

$$

MIDNIGHT CREW...MMC