703
FXCA62 TJSJ 030916
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
516 AM AST Thu Apr 3 2025

.SYNOPSIS...

Lower rain chances are anticipated today due to the arrival of a
drier airmass. Today, the main hazard will be the windy conditions,
with sustained winds of 20 to 30 mph and gusts potentially exceeding
40 mph, possibly reaching up to 50 mph in localized areas. These
wind conditions are expected to continue into Friday. These conditions
will also elevate the risk of fires, especially in grass-dominated
areas. As a result, a Fire Danger Statement (RFD) has been issued
for today.

&&

.SHORT TERM...Today through Saturday...

Showery weather persisted overnight, as gusty winds helped trigger
shower development, particularly across windward coastal areas.
Gusty wind conditions were also reported by weather stations,
especially due to passing showers. Maximum wind gusts of 25 to 30
mph were observed across the windward coastal regions of Puerto Rico
and the surrounding smaller islands. A similar weather pattern is
expected to continue through the morning hours. However, a sudden
decrease in shower activity is anticipated by this afternoon, as a
dry slot, detected by GOES-16 satellite data, moves over the area.
PWAT values are forecast to drop below 1.0 inch across the region.

Winds will increase throughout the day, with sustained winds of 20
to 30 mph and gusts potentially exceeding 40 mph, possibly
reaching up to 50 mph in localized areas. These wind conditions
are expected to continue into Friday, though slightly weaker than
today. As a result, a Wind Advisory remains in effect through 8 PM
AST Friday. These conditions could lead to difficult driving,
especially for high-profile vehicles on bridges or exposed
roadways. Tree limbs or weak trees may break and fall onto power
lines, and outdoor items could be blown around or damaged. Minor
damage to poorly secured structures is also possible. Winds will
gradually subside through the weekend, though breezy conditions
will persist as the pressure gradient over the northern Caribbean
continues to loosen.

In terms of shower activity, a mid-to-upper-level trough is expected
to deepen through the short-term forecast period. Several indicators
of favorable dynamics will be present, including 250 mb height
falls, reduced 1000-500 mb thicknesses, cooler 500 mb temperatures,
and steeper 700-500 mb lapse rates. However, moisture availability
will remain the limiting factor, with precipitable water values
falling to below-normal levels today and Friday, and 700-500 mb
relative humidity dropping nearly two standard deviations below
normal. During these drier periods, passing showers may develop
during the night and early morning hours, with scattered showers
forming in the afternoon over interior and western Puerto Rico. The
greatest potential for any thunderstorm activity is expected on
Saturday afternoon, coinciding with a brief increase in moisture
levels to near-normal values.

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

Starting the long-term period, winds will continue to subside,
allowing hazardous marine and coastal conditions to improve, at
least through next Monday. Latest model guidance continues to
suggest that a surface high-pressure over the western Atlantic
will move eastward into the Central Atlantic from Sunday into
early next week, promoting east to northeast winds to become more
easterly from Monday onward. An upper-level trough will persist
over the region through the forecast period, promoting ventilation
and cooler temperatures aloft, with 500 mb temperatures remaining
between -8C and -10C. These conditions will support favorable
conditions for deep convection and increase the chances of
thunderstorm development. However, moisture content will be
limited across different levels of the atmosphere, which could
inhibit significant rainfall and afternoon thunderstorms. Models
suggest that precipitable water values will oscillate between
below 1.0 and 1.5 inches through Tuesday, which is considered
below normal to near average. As a result, activity will likely
depend on the arrival of patches of moisture, leading to periods
of sunshine and passing showers each day. Local effects and
favorable conditions aloft will likely produce isolated to
scattered convection, with a thunderstorm or two, during the
afternoon hours across the western portions of Puerto Rico each
day. However, at the moment, significant accumulations are not
expected. By Wednesday, the arrival of a band of moisture will
produce better rain chances. From Thursday afternoon/night onward,
it seems that we will transition into a wetter pattern due to the
combination of an approaching surface frontal boundary, a pre-
frontal trough, and the arrival of abundant tropical moisture
under southeasterly wind flow across the islands. This will likely
increase the frequency and chance of showers by the end of next
week.


&&

.AVIATION...
(06Z TAFs)

Mostly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, passing SHRA will move in the
vicinity of TJSJ/TJBQ/TIST/TISX through 03/15z. E/ENE winds of  20-
25 kt will persist today, with gusts between 30 and 40 knots, but
could be higher, blo FL050. Therefore,  a Wind Advisory is in effect
for the islands.

&&

.MARINE...

A broad surface high pressure over the western Atlantic will continue
to promote fresh to locally strong east to east-northeast winds
through at least late Friday night, then conditions will gradually
improve Saturday into Sunday. Today, seas will continue to build
between 6 to 10 feet, and occasionally higher, across most waters
resulting in hazardous seas over the next few days.

&&

.BEACH FORECAST...

A broad surface high pressure over the western Atlantic is producing
strong winds across our area, especially in coastal areas today
through late Friday. This will maintain coastal conditions deteriorated
through at least Saturday. For that reason, a High Rip Current
Risk remains in effect through Saturday afternoon for the north-facing
beaches of Puerto Rico, from Aguadilla to Fajardo, Culebra and the
U.S. Virgin Islands. Also, from today through at least Friday evening
there will be a High Rip Current Risk for the beaches of southeastern
Puerto Rico, from Salinas to Yabucoa, and Vieques. A Moderate Risk is
in place elsewhere.

Swimmers are urged to exercise caution by staying near lifeguards
or even better to stay out of the water. Rip Currents can sweep
even the best swimmers away from shore into deeper water, where it
becomes difficult to return to safety. Heed the advice of lifeguards,
beach patrol flags and signs.

&&

.FIRE WEATHER...

Although most of the island has received above-normal rainfall over
the past month, smaller, fire-prone coastal regions continue to
observe below-normal precipitation. A dry slot will lead to relative
humidity values dropping to 40 to 45% across the southern coastal
plains, and possibly 50 to 55% across northwestern Puerto Rico,
an area with the lowest 30-day and 60-day percent of normal
rainfall. Combined with this dry air, windy conditions are
expected today, with easterly winds likely reaching up to 25 mph
or higher, and gusts potentially exceeding 30 mph. The KBDI was
reported at 349 in Cabo Rojo and 628 in Guanica, indicating that
areas with dry vegetation and available fuels could experience
rapid fire spread today. These conditions elevate the risk of
fast-moving fires, especially in grass-dominated areas. As a
result, a Fire Danger Statement (RFD) has been issued for the
affected regions. Please refer to RFDSJU for further details.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Saturday afternoon for PRZ001-002-
     005-008-012.

     Wind Advisory until 8 PM AST Friday for PRZ001>013.

     High Rip Current Risk through Friday evening for PRZ003-013.

VI...High Rip Current Risk through Saturday afternoon for VIZ001-002.

     Wind Advisory until 8 PM AST Friday for VIZ001-002.

AM...Small Craft Advisory until noon AST Saturday for AMZ711-712-716-
     723-726-733-741.

     Small Craft Advisory until 6 AM AST Friday for AMZ735-742-745.

&&

$$

SHORT TERM/AVIATION/FIRE WEATHER...CVB
LONG TERM/MARINE/BEACH FORECAST...YZR