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247
FXCA62 TJSJ 041700
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
100 PM AST Sun Oct 4 2026

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

.KEY MESSAGES...
Issued at 100 PM AST Sun Oct 4 2026

- Heat will remain a concern through the week, with the highest
  risk expected Monday.

- Locally heavy rainfall, flooding, and frequent lightning will
  remain possible each day, with coverage and intensity varying
  from day to day.

- A tropical wave will bring a wetter and more active pattern
  Wednesday into Thursday.

- A low rip current risk is expected Monday before a moderate risk
  returns Tuesday through Thursday along portions of the north-
  and east-facing beaches. A low risk is expected to return Friday
  into next weekend.

&&

.Short Term(This evening through Tuesday)...
Issued at 100 PM AST Sun Oct 4 2026

Lingering shower and thunderstorm activity from this afternoon may
persist into early this evening, mainly across the interior and
western to northwestern Puerto Rico, before gradually diminishing.
Thereafter, east to east-southeasterly flow will favor frequent
passing showers across eastern Puerto Rico and the U.S. Virgin
Islands overnight. Troughing west of the region may also maintain
periods of increased cloudiness, while the added cloud cover and
persistent onshore flow favor warm overnight temperatures and
limited relief from the heat.

Monday and Tuesday will feature a more typical diurnal pattern as
the trough west-northwest of the region becomes less influential and
mid-level ridging gradually strengthens. Low-level temperatures
will remain above normal, while warming aloft and modest lapse rates
should limit overall instability. Nevertheless, sufficient moisture,
strong daytime heating, sea-breeze convergence, and local terrain
effects will support afternoon showers and thunderstorms, mainly
across the interior and western to northwestern Puerto Rico.
Overnight and morning showers will continue to favor windward areas.

Heat will remain the primary hazard during the late morning and
early afternoon each day, with the greatest heat risk expected
Monday. As daytime heating triggers convection, the main concern
will transition to locally heavy rainfall, urban and small-stream
flooding, and frequent lightning during the afternoon and early
evening, particularly across the interior and western portions of
Puerto Rico.

&&

.Long Term(Wednesday through next Saturday)...
Issued at 100 PM 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 period. Precipitable water values are expected to 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
particularly 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 provide some upper-level divergence. However, guidance
continues to differ on the exact positioning of the trough. Models
also suggest an upper-level ridge just south of the region that could
limit the amount of upper-level support.

Regardless, a more active pattern is expected Wednesday into
Thursday. Windward sections will experience more frequent showers
and isolated thunderstorms, while active afternoons are anticipated
with scattered to numerous showers across the interior, western, and
northwestern portions of Puerto Rico. An elevated flood threat exists
for those areas, while a limited flood threat remains across eastern
Puerto Rico and the U.S. Virgin Islands as rounds of showers move
through. The steering flow is expected to remain mainly easterly on
Wednesday, becoming southeasterly Thursday as the wave axis crosses
the region.

As the wave departs, a transition to drier conditions and a return
to easterly flow is expected late Thursday onward, with the mid- to
upper-level ridge providing greater stability and drier air aloft. A
more seasonal pattern should return late Thursday into the weekend,
featuring typical passing showers across windward areas during the
overnight and morning hours, followed by afternoon convection across
the interior and western Puerto Rico driven by daytime heating and
local effects. A limited flood threat will continue each afternoon
in these areas. Rain streamers will also remain possible downwind
from El Yunque, the U.S. Virgin Islands, Vieques, and Culebra.

A limited heat threat is expected throughout the long-term period.
Heat-sensitive individuals should continue to take precautions,
particularly during the late morning and afternoon hours.

&&

.AVIATION...
(18Z TAFS)
Issued at 100 PM AST Sun Oct 4 2026

SHRA/TSRA over interior/W-NW PR thru early eve may produce brief
MVFR/IFR CIG/VSBY at TJBQ/TJSJ and near TJPS/USVI terminals, with
VSBY locally down to around 2SM, mtn obsc, lightning, and
gusty/VRB winds. Activity diminishes aft 00Z, with mainly VCSH
overnight at TJSJ and the USVI terminals. Winds E-ESE 10-15 kt
with higher gusts thru 04/22-23Z, becoming light/VRB overnight,
then increasing again aft 05/13Z.

&&

.MARINE...
Issued at 100 PM AST Sun Oct 4 2026

A surface high moves east as a frontal low enters the western
Atlantic, easing the pressure gradient and resulting in light to
moderate east to east-southeast winds. Troughing west of the region
will help maintain shower and thunderstorm activity this afternoon
and tonight. Winds increase somewhat Tuesday into Wednesday with
another surface high building over the western Atlantic. Seas will
range from 3 to 4 feet, occasionally higher. A tropical wave
crossing late Wednesday into Thursday will increase shower and
thunderstorm activity.

&&

.BEACH FORECAST...
Issued at 100 PM AST Sun Oct 4 2026

A moderate risk of rip currents will persist along the north- and
east-facing beaches of Puerto Rico and Culebra this afternoon and
tonight. The risk will remain low elsewhere; however, life-
threatening rip currents can still occur near groins, jetties,
reefs, and piers. A more widespread low rip current risk is expected
Monday before a moderate risk returns Tuesday through Thursday
along the north- and east-facing beaches of Puerto Rico, the U.S.
Virgin Islands, Vieques, and Culebra. A low risk is expected to
return Friday into the weekend.

A daily afternoon lightning risk will also affect local beaches,
primarily across northern and western Puerto Rico. High heat indices
will persist during the late morning and afternoon, especially
along exposed coastal areas.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

EVE...ERG/KML
MID...YZR
DAY...ICP/MRR

NWS SJU Office Area Forecast Discussion