722
FXCA62 TJSJ 051910
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
310 PM AST Sun Oct 5 2025

.KEY MESSAGES...

* A strong, long-period northeasterly swell will continue to
  produce hazardous beach and marine conditions through at least
  early Tuesday.

* A tropical wave advancing across the eastern Caribbean will
  enhance shower and thunderstorm activity across our region by
  Monday and Tuesday. Limited to elevated flood risk will persist.

* Across the U.S. Virgin Islands, occasional passing showers and
  a few thunderstorms are still expected with a limited flood
  risk.

&&

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

Showers affected eastern Puerto Rico, the U.S. Virgin Islands, and
adjacent islands during the morning hours. By late morning, a San
Juan streamer developed, producing frequent lightning and heavy
downpours, with rainfall totals of nearly 2 inches between Canovanas
and Carolina. As the day progressed, daytime heating and local
effects triggered additional convection across western sections of
the USVI and nearby islands, while more intense thunderstorm
development expanded across much of Puerto Rico. Rainfall estimates
have already reached around 2 inches in several areas, with amounts
still increasing. Multiple Special Weather Statements, Flood
Advisories, and even a Severe Thunderstorm Warning were issued in
response to the active weather. Afternoon highs peaked in the low to
mid-90s, while heat indices soared into the mid to upper 100s,
reaching as high as 112F in isolated spots. Winds remained gentle
to moderate at 1014 mph, strengthened at times by strong sea-breeze
variations.

This evening and overnight, a weak upper-level low remains parked
just to the west of the islands, while mid-level temperatures near -
6.5C continue to hold at climatological values. Although the bulk
of instability will remain limited, above-normal precipitable water
values around 1.9 inches will be sufficient to support isolated to
scattered showers and a few thunderstorms. Activity will favor the
windward and eastern to northern sections of Puerto Rico, the U.S.
Virgin Islands, and adjacent islands. Conditions will gradually
taper off overnight, with light northeasterly winds likely bringing
slightly cooler conditions. A few brief downpours and occasional
gusty winds remain possible, but widespread hazards are not
anticipated.

By Monday and into Tuesday, attention turns to a tropical wave
advancing into the eastern Caribbean. This system, combined with
typically cool mid-level temperatures and a deepening moisture
plume, will enhance shower and thunderstorm activity, with
precipitable water values climbing above normal and peaking near 2.1
inches on Tuesday. Winds will gradually back from the northeast on
Monday before veering to the southeast Tuesday, steering convection
inland and favoring western and southwestern Puerto Rico Monday
afternoon, then becoming more widespread and organized on Tuesday as
activity shifts northward. Hazards include frequent lightning,
ponding of water on roadways, and localized flooding. The flood risk
will significantly increase on Tuesday, when urban and small-stream
flooding is likely and isolated flash floods are possible. In
addition, gusty winds, small hail, and even isolated funnel clouds
will remain possible, particularly during the peak heating hours.
Temperatures will remain seasonably warm, but greater cloud cover
and convection should limit excessive heat stress, though Tuesday
may feel the warmest as southeasterly flow develops and moisture
peaks.

.LONG TERM...Wednesday through Sunday...
.PREV DISCUSSION... /issued 552 AM AST Sun Oct 5 2025/

An upper-level low northeast of the region will begin to move
away from the area by Wednesday. Subsequently, a mid-to-upper
level ridge will take place across the area, promoting drier air
intrusion and stable conditions aloft from Wednesday into
Thursday. The latest precipitable water (PWAT) analysis indicates
normal climatological values throughout much of the period.
Additionally, the 500mb temperatures will also remain within
normal values (between 6 to 7 degrees Celsius) during the
period.

By Thursday, moisture will slightly increase with the arrival of an
atmospheric disturbance, promoting showers and isolated
thunderstorms across the area. Under this moist pattern and with
southeasterly winds, the shower activity will be expected toward the
central and northwestern municipalities of Puerto Rico. For the U.S.
Virgin Islands, showery weather is anticipated each morning across
the islands. Winds will prevail mostly from the southeast in
response to a surface high pressure in the central Atlantic.
However, by the end of the period, the steering winds will depend on
the potential development of a tropical wave near the islands.

The second half of the forecast will depend on the development of a
broad tropical wave located south of the Cabo Verde Islands. The
National Hurricane Center (NHC) is monitoring the aforementioned
wave with a low formation chance (30%) in the next 48 hours, and a
medium formation chance (60%) in the next 7 days. The latest model
guidance continues to suggest an increase in moisture content
associated with this system from Friday onwards. At this time, there
is high uncertainty in terms of the trajectory and intensity of this
wave. Residents and visitors are urged to continue monitoring the
progress of this system as it moves over the Atlantic Ocean.

&&

.AVIATION...
(18Z TAFs)

SHRA/TSRA will continue through 05/23Z, producing mountain
obscuration and brief periods of MVFR to IFR conditions at all PR
terminals, mainly due to reduced visibility and low ceilings. Across
the USVI, most activity will remain in the vicinity with limited
operational impacts. After 05/23Z, VCSH/VCTS will remain possible
over northern PR terminals and the USVI. Surface winds will stay
gentle to moderate from the east-southeast at 814 kt with sea-
breeze variations, becoming light to calm after 05/23Z, except for
gusty and variable conditions near SHRA/TSRA. Winds will gradually
back from the northeast tonight.

&&

.MARINE...

Light to moderate east to northeast winds across the islands
tonight and Monday. The long-period northeasterly swell will
continue to spread across the Atlantic waters and passages through
at least early Tuesday, deteriorating marine and coastal
conditions. Small Craft Advisories remain in effect until Monday
night. A tropical wave will approach the region tomorrow, Monday,
increasing the frequency of showers early this upcoming workweek.

&&

.BEACH FORECAST...

The strong long-period northeasterly swell will continue to produce
hazardous beach conditions through at least tomorrow night or
early Tuesday along the Atlantic exposed beaches. As a result, the
high risk of life-threatening rip currents continues through at
least Tuesday afternoon across western, northern, eastern coasts
of Puerto Rico, Culebra, Vieques and U.S. Virgin Islands.

The Coastal Flood Warning and High Surf Warning will likely expire
at 6 PM or will be downgraded earlier for the northern and eastern
coasts of Puerto Rico. After that, A High Surf Advisory will remain
in place for mentioned areas and also including the western coast
of Puerto Rico, Culebra and U.S. Virgin Islands through at least
6 AM AST Tuesday. Potential impacts include: high waves that can
wash over jetties and sweep people and pets onto jagged rocks.
Large breaking waves will result in localized beach/dune structure
erosion and dangerous swimming conditions, as well as minor
coastal flooding in the most vulnerable areas.

Residents and visitors are strongly encouraged to keep an eye on
the beach forecast and follow the beach flag warning system.
Beachgoers, dont take unnecessary risks, it`s safest to stay out
of the water at least through next Tuesday! For more information
about each hazard, please consult our Coastal Hazard Message
(CFWSJU).

[Next high tides: Fajardo at 7:11 PM AST (1.55 ft), La Puntilla,
San Juan at 7:32 PM AST (1.61 ft), Arecibo at 7:03 PM AST (1.74
ft), and Crash Boat, Aguadilla at 6:54 PM AST (1.58 ft)].


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Coastal Flood Warning until 6 PM AST this evening for PRZ001-002-
     005-008.

     High Rip Current Risk through Tuesday afternoon for PRZ001-002-
     005-008-010-012-013.

     High Surf Warning until 6 PM AST this evening for PRZ001-002-005-
     008.

     High Surf Advisory from 6 PM this evening to 6 AM AST Tuesday
     for PRZ001-002-005-008.

     High Surf Advisory until 6 AM AST Tuesday for PRZ010-012.

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

     High Surf Advisory from 6 PM this evening to 6 AM AST Tuesday
     for VIZ002.

     High Surf Advisory until 6 AM AST Tuesday for VIZ001.

AM...Small Craft Advisory until midnight AST Monday night for AMZ711-
     712-716-723-741-742.

&&

$$

ICP/YZR