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396
FXCA62 TJSJ 121715
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
115 PM AST Mon Oct 12 2026

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

.KEY MESSAGES...
Issued at 1252 PM AST Mon Oct 12 2026

 - Expect, limited to elevated flooding threat through at least
   midweek due to increasing moisture and atmospheric instability
   as a mid-to-upper level low continues over and west of the
   islands.

 - Limited heat risk for Puerto Rico and the US Virgin Islands through
   the workweek, please continue to monitor the forecast for any
   updates.

 - Weaker winds on Tuesday will favor slower moving thunderstorms
   and higher localized rainfall totals across Puerto Rico and the
   US Virgin Islands.

 - Moderate rip current risk will prevail along the northern and
   eastern beaches of Puerto Rico and Saint Croix from Tuesday
   onwards, elsewhere low rip current risk.

&&

.Short Term(This evening through Wednesday)...
Issued at 1252 PM AST Mon Oct 12 2026

A relatively moist, unstable air mass will remain entrenched across
the region for the next few days, while an upper-level low southwest
of the region slowly moves north across Hispaniola through the short-
term period. Recent soundings and satellite moisture tracking
indicate total precipitable water values hovering between 1.90 and
2.10 inches, well above mid-October climatological normals. This
abundant moisture, coupled with surface CAPE above 2000 J/kg and a
light southeasterly low-level wind profile, will promote deep
convective development this afternoon, mainly from north-central to
western Puerto Rico. Weak steering winds will promote slow-moving
showers and increase the threat of urban and small-stream flooding.
The upper low will promote divergence aloft and colder-than-normal
mid-level temperatures, which can produce strong thunderstorms that
may produce small hail, gusty winds, and frequent cloud-to-ground
lightning.

Through Tuesday, strong diurnal heating, sea breeze convergence, and
terrain interaction will drive the weather along favorable upper-
level dynamics. Afternoon showers and thunderstorms will concentrate
primarily across the interior and western Puerto Rico, as well as
downwind of the U.S. Virgin Islands. High-resolution model guidance
indicates rainfall accumulations of 1.50 to 2.50 inches, with the
highest totals over western PR. Given the soil moisture content
across the western municipalities, urban and small-stream flooding
alongside rapid river rises will remain the main hazards. Shower
coverage is expected to trend downward by Wednesday as mid-level
moisture slightly diminishes gradually. However, isolated heavy
showers and thunderstorms are still expected over west-southwest PR
as winds gradually shift more east to northeast from late Tuesday
through Wednesday.

Across coastal and urban areas, light winds and high surface
dewpoints will keep conditions humid. Daytime highs in the upper 80s
to lower 90s will push heat indices above 100F daily, with localized
areas in northern and western Puerto Rico briefly exceeding 105F.
However, given the expected weather and ENE winds, heat advisory
conditions are not expected across the islands.

&&

.Long Term(Thursday through next Sunday)...
Issued at 1252 PM AST Mon Oct 12 2026

Stable conditions should prevail through the end of the workweek,
then become wetter and unstable by early next week. A frontal
boundary that induces a prefrontal trough north of the CWA should
maintain an E-ENE wind flow on Thursday and Friday, briefly shifting
to E-SE on Saturday as a surface high pressure exiting eastern CONUS
builds over the Western Atlantic, then back to E-ENE by Sunday. In
the mid to upper levels, a ridge north of the region should bring
more stable conditions, with warmer-than-normal mid-level
temperatures (up to -4 C), leading to subsidence across the area,
unfavorable for deeper convection. However, the vicinity of a
departing upper-level low, abundant moisture (PWATs around 1.75) in
the low and mid levels combined with local effects could aid
afternoon convection over western/southwestern Puerto Rico. Friday
is forecast as the less active day of the period, as a drier slot in
the mid levels (between 30 and 40 %), limiting shower activity.
Afternoon convection can still be expected, though thunderstorms, if
any, should remain isolated and short-lived. Although the dry mid-
levels could persist on Saturday and guidance suggests low wind
shear in the low to mid levels, E-SE winds should enhance daytime
heating and the sea breeze convergence effect, along with the
vicinity of an upper-level low, leading to isolated showers and
thunderstorms over northwestern Puerto Rico. Conditions may
gradually deteriorate by Sunday morning, as guidance suggests the
approach of another retrogressive TUTT into the Caribbean,
introducing instability. The latest model solutions suggest slightly
colder than normal mid-level temperatures (below -7 C), with an
increase in moisture content in the mid levels and steeper lapse
rates. Under this scenario, an advective pattern is likely on Sunday
morning across windward sections of the islands, followed by deep
convection across interior and western Puerto Rico and local island
streamers.

Overall, showers and thunderstorms can be expected each day, with
less chance of flooding on Friday. On Thursday and Saturday, mainly
ponding of water over roadways and poorly drained areas is expected,
with minor flooding. With the approach of the retrogressive TUTT,
Sunday is likely to be the wettest day of the period, increasing
the chance of urban and small stream flooding across western Puerto
Rico.

&&

.AVIATION...
(18Z TAFS)
Issued at 1252 PM AST Mon Oct 12 2026

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, +SHRA/TSRA over western PR may
cause tempo MVFR to brief IFR conds at TJBQ thru 12/22z. Elsewhere,
mostly VCSH expected. The 12/12z TJSJ sounding indicated ESE winds
up to 20 kt blo FL030. Light and variable winds expected overnight,
bcmg E-ENE at 10-15 kt aft 13/13z.

&&

.MARINE...
Issued at 1252 PM AST Mon Oct 12 2026

Lingering upper-level low will continue to promote showers and
isolated thunderstorms across the regional waters through midweek.
High pressure over the central Atlantic will maintain moderate
east- southeast winds, though winds will gradually diminish
through Tuesday. Choppy seas will persist across portions of the
offshore Caribbean and Atlantic waters before gradually improving.
Lighter east to east-southeast winds and generally lower seas are
expected from Tuesday into midweek. Mariners should remain alert,
as thunderstorms may locally produce gusty winds, higher seas,
frequent lightning, and reduced visibility.

&&

.BEACH FORECAST...
Issued at 1252 PM AST Mon Oct 12 2026

Low rip current risk through tonight across the beaches of Puerto
Rico and the U.S. Virgin Islands. Although the overall risk is
low, localized rip currents can still occur, particularly near
jetties, piers, and other structures. Beachgoers should continue
to exercise caution in the surf zone. From late Tuesday onwards,
moderate rip current risk will prevail mainly over the northern
and east facing beaches of Puerto Rico, Culebra, potentially Saint
Croix.

&&

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

$$

SHORT TERM/AVIATION...DSR
LONG TERM...MNG
MARINE/BEACH FORECAST...MMC

NWS SJU Office Area Forecast Discussion