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596
FXCA62 TJSJ 111739
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
139 PM AST Sun Oct 11 2026

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

.KEY MESSAGES...
Issued at 125 PM AST Sun Oct 11 2026

 - A limited to elevated flooding threat is expected from Monday
   through Wednesday due to increasing moisture and atmospheric
   instability.

 - A limited heat threat is expected on Monday, particularly
   across coastal and urban areas.

 - Relatively tranquil marine conditions will prevail, with seas
   up to 5 feet.

 - A moderate risk of rip currents will persist along portions of
   the local beaches.

&&

.Short Term(This evening through Tuesday)...
Issued at 125 PM AST Sun Oct 11 2026

Variable weather conditions prevailed across the region during the
morning hours, with showers affecting portions of southeastern and southern
Puerto Rico, where rainfall accumulations fluctuated between 1
and 2 inches. By around 10 AM AST, shower activity had diminished
over land areas but continued across the surrounding waters,
associated with an area of low pressure moving from east to west
across Puerto Rico and its associated unstable conditions. At
around 12 PM AST, Doppler radar indicated additional shower
activity across portions of the U.S. Virgin Islands, where
thunderstorms developed over St. Croix, producing wind gusts
between 30 and 40 mph. These showers continued moving westward,
reaching the eastern coastal sections of Puerto Rico. In terms of
temperatures, maximum temperatures reached the lower 90s across
coastal and urban areas, while temperatures remained in the lower
80s across the mountainous sections due to increased cloud
coverage and shower activity.

The latest guidance suggests a gradual increase in moisture and
atmospheric instability across the region from Monday into
Tuesday. Precipitable water values will fluctuate between 1.70 and
2.20 inches, with the highest moisture content expected from late
Monday into Tuesday. Meanwhile, a cut-off low moving from east to
west across the region will result in lower 250 mb heights on
Monday, followed by a gradual increase toward Tuesday as the
upper-level feature moves westward. Temperatures at 500 mb will
remain relatively cool, fluctuating between -6C and -8C,
providing additional support for atmospheric instability. The
combination of increasing moisture and favorable upper-level
conditions will support a more unstable weather pattern, enhancing
the potential for showers and thunderstorms across the local
islands. Therefore, the forecast calls for variable weather
conditions on Monday, with passing showers along windward areas,
followed by afternoon showers across the northwestern quadrant of
Puerto Rico due to the east-southeasterly wind flow associated
with a broad surface high-pressure system over the central
Atlantic.

On Tuesday, winds at 925 mb will gradually weaken from around 17
knots to between 7 and 12 knots, allowing local effects and sea
breeze convergence to play a greater role in afternoon convective
development. Although showers and thunderstorms are expected on
Monday, atmospheric conditions will become more favorable for
widespread convective development on Tuesday as moisture and
instability increase across the region. Additionally, the Galvez-
Davison Index suggests a high potential for isolated to scattered
thunderstorms on Tuesday. Therefore, Tuesday is expected to be the
wettest and most unstable day of the long-term period, with
locally heavy rainfall and frequent lightning remaining the
primary hazards. An increased potential for urban and small stream
flooding is also expected, particularly across areas experiencing
repeated or prolonged rainfall associated with slow-moving
showers and thunderstorms over the interior sections of Puerto
Rico.

Although flooding and lightning will remain the primary hazards
due to the enhanced atmospheric instability, temperatures at 925
mb will remain relatively warm throughout the period, supporting
warm conditions across coastal and urban areas each day.

&&

.Long Term(Wednesday through next Saturday)...
Issued at 125 PM AST Sun Oct 11 2026

The retrograding mid-to-upper-level low will dominate the area
through Thursday before exiting by the end of the long-term period,
promoting more seasonal conditions. Latest guidance still suggests
500 mb temperatures will drop below -7 degrees Celsius on Wednesday
and Thursday, causing steep mid-level lapse rates. Associated with
this synoptic feature, an induced inverted surface trough will
continue to favor low-level convergence and seasonal to above-normal
PWAT values around 1.85 to 2.25 inches. Combined with daytime
heating and local effects, this could support deep, organized
convection through Thursday. By Friday and Saturday, a more seasonal
pattern is expected as the mid-to-upper-level low exits the area;
hence, less moisture is anticipated, particularly in the mid-levels.
However, local effects and lingering low-level moisture could still
promote shower and thunderstorm activity.

On Wednesday, light to gentle east-southeasterly winds will favor
slow-moving showers and thunderstorms, primarily over the interior
to northwestern sections of Puerto Rico. By Thursday, model guidance
still suggests a frontal boundary exiting the eastern CONUS and
inducing a pre-frontal trough north of the CWA. This will shift
winds to an ENE flow on Thursday, focusing convection over the
interior and southwestern Puerto Rico. By the end of the period,
winds are expected to shift gradually to an east to east-
southeasterly flow, driving activity mainly toward interior and
western Puerto Rico on Friday, and northwestern sections from
Saturday onwards. Regardless, passing showers and thunderstorms
cannot be ruled out across eastern Puerto Rico and the USVI each day.

These conditions will maintain a limited to elevated risk of
flooding through Thursday, with urban and small stream flooding and
flash flooding possible, particularly on Wednesday, when lighter
winds will favor slow-moving showers with higher rainfall
accumulations. In addition, localized strong wind gusts and frequent
lightning are expected with the strongest thunderstorms.

&&

.AVIATION...
(18Z TAFS)
Issued at 125 PM AST Sun Oct 11 2026

SHRA/TSRA will continue to develop and move across portions of PR
and the USVI, resulting in reduced VIS and lower CIGS at all
terminals through at least 11/22-23Z. Periods of MVFR/IFR conds are
possible in heavier SHRA/TSRA, along with mtn obsc, particularly at
TJBQ/TJPS. ESE winds 15-20 kt thru 11/23Z, becoming light/VRB
overnight. Additional SHRA will result in VCSH/-SHRA at
TJSJ/TIST/TISX aft 12/13Z.

&&

.MARINE...
Issued at 125 PM AST Sun Oct 11 2026

An upper-level low and associated surface trough will promote
scattered showers and isolated thunderstorms across the regional
waters through early this week. A high pressure system located over
the central Atlantic will maintain moderate to locally fresh east-
southeast winds through Monday, keeping seas moderately choppy to
choppy. As the high shifts farther east, the pressure gradient will
relax, allowing winds to diminish to light-to-gentle breezes Tuesday
and Wednesday. High pressure building across the western Atlantic
behind a cold front will encourage an east-to-east-northeast flow
later in the week. Mariners should note that thunderstorms may
locally produce higher winds, elevated seas, frequent lightning, and
reduced visibility.

&&

.BEACH FORECAST...
Issued at 125 PM AST Sun Oct 11 2026

A moderate risk of rip currents will persist today across the north-
and east-facing beaches of the islands. Beachgoers should exercise
caution, as life-threatening rip currents remain possible in the
surf zone. The rip current risk will become low by Monday, though it
may increase again by mid-week.

Beachgoers are encouraged to remain weather-aware, as showers and
thunderstorms are expected daily, with the most active weather
occurring early this week across the islands. Thunderstorms
approaching coastal areas may bring localized heavy rainfall, gusty
winds, and lightning. Always seek shelter immediately if you hear
thunder.

&&

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

$$

SHORT TERM & KEY MESSAGES...LIS
LONG TERM....JCP
AVIATION, MARINE & BEACH FORECAST...GRS

NWS SJU Office Area Forecast Discussion