704
FXCA62 TJSJ 040730
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
330 AM AST Sun Oct 4 2026

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 330 AM AST Sun Oct 4 2026

- A Heat Advisory is in effect from 10 AM to 4 PM AST this
  afternoon across Puerto Rico and the U.S. Virgin Islands. Heat
  will likely remain a persistent risk over the coming days,
  particularly before the development of afternoon rain and in
  areas where rainfall remains limited.

- Showers and thunderstorms posing a limited to elevated flood
  risk will continue to develop this afternoon and into early next
  week, mainly across the interior and western Puerto Rico.

- The potential for more widespread activity will increase from
  Wednesday into Thursday as moisture associated with a tropical
  wave moves into the region. This could increase the risk of
  locally heavy rainfall, flooding, and stronger thunderstorms.

- There is a moderate risk of rip currents along the northern and
  eastern beaches of Puerto Rico and Culebra today. Similar
  conditions are expected to persist over the coming days, but the
  risk will also extend to the beaches of the U.S. Virgin Islands.

&&

.Short Term(Today through Tuesday)...
Issued at 330 AM AST Sun Oct 4 2026

Overall, conditions remained relatively calm overnight, with
partly cloudy skies and light, variable winds. Passing showers
affected the local waters and windward portions of Puerto Rico
and the U.S. Virgin Islands, although radar estimates indicated
no significant rainfall accumulations since midnight. More
frequent showers and thunderstorms were observed farther north
across the Atlantic waters and near Hispaniola, where a mid- to
upper-level trough remained present. Surface observations and
weather stations reported minimum temperatures generally in the
upper 70s to lower 80s.

The forecast for today, Sunday, is expected to feature a typical
diurnal weather pattern, with winds gradually becoming more east-
southeasterly. An upper-level trough will remain positioned near
Hispaniola, keeping Puerto Rico along its eastern flank and
providing only limited large-scale support. Latest satellite-
derived Precipitable Water (PWAT) imagery indicates that values
will remain near seasonal levels, ranging from 1.7 to 1.9 inches,
although some drier air is present between approximately 700 and
500 mb as a mid level ridge begind to set. As a result, afternoon
showers and thunderstorms will be driven mainly by local effects
such as daytime heating, sea-breeze interactions, and available
moisture, with the greatest activity expected across the
Cordillera Central and western to northwestern Puerto Rico.

This afternoon, an elevated flood threat remains in place,
particularly across portions of the interior and western to
northwestern Puerto Rico. A limited flood threat remains across
portions of eastern Puerto Rico and the metropolitan area due to
the potential development of El Yunque and U.S. Virgin Islands
streamers. An elevated flood threat means flooding is possible in
urban areas, along roads, and in small streams and washes, while a
limited flood threat indicates that ponding of water is possible
on roads and in poorly drained areas. Similar conditions are
expected on Monday and Tuesday. Mornings should remain relatively
quiet, with only limited shower activity. During the afternoon,
convection is expected to increase as lingering low-level moisture
combines with daytime heating, local terrain effects, and sea-
breeze interactions.

Heat concerns will persist today and are likely to extend into
early next week as temperatures in the lower levels of the
atmosphere continue to rise. Guidance indicates 925-mb
temperatures near the 75th percentile, or approximately two
standard deviations above normal. The primary concern during the
late morning and early afternoon will be heat, followed by an
increasing threat of localized heavy rainfall and flooding where
thunderstorms develop. Residents and visitors are encouraged to
remain hydrated and stay weather aware, as conditions may change
rapidly during the afternoon.

&&

.Long Term(Wednesday through Sunday)...
Issued at 330 AM AST Sun Oct 4 2026

A tropical wave crossing the local area Wednesday into Thursday will
bring the best opportunity for showers and thunderstorms during the
long-term forecast period. Precipitable water (PWAT) values will
increase to 2.1-2.3 inches, which is above average for this time
of year. Despite the wave, mid- to upper-level support is not
expected to be very favorable. A mid-level ridge to the north will
keep mid-level lapse rates only modestly steepened with little
cooling at 500 mb. Meanwhile, an upper-level trough just northeast
of the local area could produce some upper-level divergence.
However, guidance disagrees on the exact positioning of the
trough. Models also suggest an upper-level ridge just south of the
region that could shield the area from upper-level divergence.

Regardless, a more active pattern is expected Wednesday, Wednesday
night, and into Thursday. Windward sections will experience more
frequent showers and isolated thunderstorms. Active afternoons are
also anticipated, with scattered to numerous showers across the
interior to western and northwestern portions of the islands. An
elevated flood threat exists for those areas, while a limited flood
threat remains across eastern Puerto Rico and the USVI as rounds of
showers cross the area. The steering flow is expected to be mainly
easterly on Wednesday, shifting to southeasterly on Thursday as the
wave axis crosses the area.

As the wave departs, a transition to drier conditions and a return
of easterly flow is expected late Thursday onward, with the mid- to
upper-level ridge providing increased stability and drier air aloft.
Therefore, a seasonal pattern returns late Thursday into the early
weekend, featuring typical passing showers across windward areas
during the overnight and morning hours, followed by afternoon
convection across interior to western Puerto Rico driven by diurnal
heating and local effects. A limited flood threat will continue each
afternoon for those areas. Rain streamers will also be possible each
afternoon downwind from El Yunque, the USVI, Vieques, and Culebra.

A limited heat threat is expected throughout the long-term period.
Extremely sensitive individuals could be affected and should take
precautions to protect themselves from heat conditions.

&&

.AVIATION...
(06Z TAFS)
Issued at 330 AM AST Sun Oct 4 2026

Mainly VFR conds are expected across all terminals through the
forecast period. Passing -SHRA/VCSH across TJSJ and the USVI
terminals during the morning hrs. Aft 04/16-17Z, SHRA/TSRA are
expected to develop across the interior and W/NW PR, producing
VCTS at TJBQ/TJPS and TJSJ. Expect intermittent/brief MVFR conds
due to vis reductions and mountain obsc. E-ESE winds will increase
aft 13Z to 10-12 kt, with sea breeze variations and slightly
higher gusts. Light and variable winds overnight.

&&

.MARINE...
Issued at 330 AM AST Sun Oct 4 2026

Surface high will shift toward the east on Sunday, relaxing the
pressure gradient a little. As a result, winds will become light
to moderate and seas will gradually subside. Easterly trade winds
are expected to strengthen again by Tuesday into Wednesday as
another surface high builds across the western Atlantic, resulting
in increasingly choppy marine conditions. A tropical wave will
move over the Caribbean Sea late Wednesday into Thursday,
increasing the potential for showers and thunderstorms.

&&

.BEACH FORECAST...
Issued at 330 AM AST Sun Oct 4 2026

For the north and east facing beaches of the local islands, the
risk of rip currents will be moderate today, and low on Monday.
The risk elsewhere will be low.

There is a risk of lightning each afternoon across the local
beaches, mostly in the western and northern half of Puerto Rico.
Seek shelter immediately if thunder is heard.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for PRZ001>013.

VI...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM/AVIATION...YZR
LONG TERM...KML
MARINE/BEACH...ERG