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957
FXCA62 TJSJ 261837
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
237 PM AST Mon Oct 26 2026

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

.KEY MESSAGES...
Issued at 227 PM AST Mon Oct 26 2026

- A Heat Advisory remains in effect until 5 PM AST this afternoon
  for Puerto Rico and the U.S. Virgin Islands. Hot and humid
  conditions will increase the risk of heat-related illnesses,
  especially for individuals without adequate cooling or
  hydration. Elevated heat impacts are expected to persist through
  Tuesday.

- Dangerous marine and coastal conditions continue across the coastal
  waters and beaches of western, northern, and eastern Puerto
  Rico, as well as Culebra, due to incoming pulses of northerly
  swell. Small Craft Advisories, a High Rip Current Risk, and High
  Surf Advisories are in effect. Please refer to the Marine and
  Beach Forecast sections below for specific details.

- A drying trend is anticipated over the coming days, bringing
  generally fair weather across Puerto Rico and the U.S. Virgin
  Islands. However, pockets of low-level moisture will bring
  occasional passing showers, primarily across northwestern,
  southern and southeastern Puerto Rico during the afternoon and
  overnight hours. A few isolated thunderstorms cannot be ruled out.



&&

.Short Term(This evening through Wednesday)...
Issued at 227 PM AST Mon Oct 26 2026

A southeasterly advective pattern prevailed across the region this
morning, with a few passing showers affecting mainly the
southeastern coastal areas of Puerto Rico. Otherwise, mostly fair
weather conditions prevailed across much of the region, allowing
temperatures to rise quickly. By noon, several weather stations
across southwestern and north-central Puerto Rico had already
reached Heat Advisory criteria, with hot and humid conditions
expected to maintain an increased heat risk through the rest of the
afternoon.

For the remainder of today, southeasterly flow will continue to
transport moisture across the region, with precipitable water
gradually increasing toward 1.8 to 1.9 inches. However, a ridge at
the mid and upper levels, accompanied by relatively warm
temperatures aloft, dry mid-levels, and modest lapse rates, will
limit deep convection. Although daytime heating, sea breeze
convergence, and local effects could still support isolated
afternoon showers and thunderstorms across the interior and
northwestern Puerto Rico, confidence in convective coverage remains
low. Meanwhile, persistent southeasterly flow will favor additional
showers across southern and southeastern Puerto Rico, where locally
heavy rainfall could lead to ponding of water on roads and in poorly
drained areas, as well as isolated urban and small-stream flooding.
Similar activity could affect Vieques and the surrounding southern
waters.

On Tuesday, a trough over the western Caribbean and a ridge over the
eastern Caribbean will maintain a southeasterly flow, continuing to
transport tropical moisture across the region. Both GFS and ECMWF
guidance suggest precipitable water increasing toward 1.9 to 2.0
inches, with relatively high moisture content at low levels.
Nevertheless, the persistent ridge aloft and relatively warm 500-mb
temperatures will maintain modest mid-level lapse rates, limiting
widespread deep convection despite the increasing moisture. While
local effects and daytime heating could support isolated afternoon
thunderstorms across portions of the interior and northwestern
Puerto Rico, uncertainty remains regarding their coverage and
intensity. Recent NBM and ECMWF ensemble rainfall guidance suggests
a greater potential for rainfall across southern and southeastern
Puerto Rico and the surrounding southern waters, including portions
of the smaller islands. Locally heavy or repeated showers could
result in ponding of water in roadways and in poorly drained areas,
particularly across southern and southeastern Puerto Rico.

By Wednesday, a gradual weakening of the ridge aloft will allow 500-
mb temperatures to cool and mid-level lapse rates to steepen
slightly, potentially providing a more favorable environment for
convection. However, both GFS and ECMWF guidance indicate decreasing
moisture, with considerable differences in the magnitude of drying.
While the GFS maintains precipitable water generally between 1.6 and
1.8 inches, the ECMWF suggests a more pronounced dry intrusion, with
values dropping toward 1.3 to 1.5 inches. This introduces
uncertainty regarding the coverage and intensity of showers and
thunderstorms. Nevertheless, lingering moisture, daytime heating,
and local effects could still support afternoon convection across
portions of Puerto Rico, particularly where sufficient moisture
persists. The wetter GFS solution would favor greater convective
coverage, while the drier ECMWF solution would limit rainfall
activity despite gradually improving lapse rates.

Above-normal temperatures and humid conditions will maintain an heat
risk through Tuesday, particularly across coastal and urban areas of
Puerto Rico and the U.S. Virgin Islands. Some relief is anticipated
by Wednesday as drier air moves into the region, although
temperatures will remain warm, especially across coastal and urban
areas.

&&

.Long Term(Thursday through Monday)...
Issued at 353 AM AST Mon Oct 26 2026

No major changes were introduced to the long-term forecast, as
wetter and more unstable conditions continue to be forecast this
weekend. The latest model guidance continues to suggest a surface
high pressure over the Central Atlantic interacting with a polar
trough deepening into the tropics, maintaining an ESE-SE wind flow
throughout the forecast period. A mid-to-upper level ridge northeast
of the CWA should continue to dominate the weather pattern on
Thursday, as guidance suggests warmer-than-normal 500 mb
temperatures (above -6 C) and low mid level lapse rates, indicating
unfavorable conditions for deep convection. Additionally, the Galvez-
Davison Index (GDI) suggests shallow convection on Thursday
afternoon across the mountain ranges of Puerto Rico. As mentioned
in the previous discussions, PWAT values should remain below
climatological normal (below 1.75 inches), with the dry slot in
the low and mid levels. Although daytime heating combined with
local effects and sea breeze convergence should aid in breaking
the cap inversion and allow shower and thunderstorm activity,
rainfall accumulations should remain minimal.

Friday onwards, global models continue to suggest wetter and
unstable conditions across the CWA, as the trough approached the
CWA, weakening the ridge, leading to divergence aloft and
enhancing instability. Additionally, the latest NCICS forecast
continues to suggest the Madden-Julian Oscillation (MJO) over the
CWA, which may enhance upward motion and divergence aloft. The
latest deterministic guidance from the GFS and ECMWF suggests PWAT
values could reach up to 2.25 inches, slightly above normal,
mainly in the low and mid levels. Additionally, the guidance
suggests skinny-sounding profiles, with high CAPEs, and cooler-
than-normal mid-level temperatures (between -6 and -8 C), and
stronger upper- winds, allowing cloud growth and ventilation.
Therefore, the most likely scenario remains, with an advective
pattern across windward sections of the islands early Saturday,
followed by deep afternoon convection across mountain ranges of
Puerto Rico, including the San Juan Metro Area. Rainfall
accumulations could lead to urban and small stream flooding,
without ruling out flash flooding. Additionally, rivers may rise
quickly. Therefore, the flood threat will remain limited to
elevated across the aforementioned areas on Friday, Saturday, and
Sunday. Besides flooding, thunderstorms could produce gusty winds
and frequent lightning.

&&

.AVIATION...
(18Z TAFS)
Issued at 227 PM AST Mon Oct 26 2026

Mainly VFR conds expected across all terminals thru the fcst period.
SE winds at 10-15 kt with hir gusts thru 22Z, bcmg lgt overnight.
VCSH expected at TJSJ/TJBQ thru 22Z, with -SHRA at TJPS thru 02Z and
brief MVFR conds psbl thru 27/10Z. ESE-SE winds at 10-15 kt expected
Tue with gusts up to 20 kt across eastern terminals.

&&

.MARINE...
Issued at 227 PM AST Mon Oct 26 2026

Surface high pressure over the central Atlantic will promote
moderate to locally fresh east-to-southeasterly winds across the
region through midweek. A long-period northerly swell is expected to
spread across the Atlantic waters and local passages today, building
seas to 6 to 8 feet through Tuesday. Small Craft Advisories remain
in effect for the Atlantic offshore waters and the Mona Passage
through Tuesday afternoon. Isolated thunderstorms are forecast to
develop mainly over Caribbean waters, the Mona Passage, and offshore
Atlantic waters over the next few days.

&&

.BEACH FORECAST...
Issued at 227 PM AST Mon Oct 26 2026

A long-period northerly swell will arrive today, with additional
pulses expected through midweek. This swell will generate breaking
waves of 6 to 12 feet, creating rough surf and life-threatening rip
currents, primarily along north-facing beaches of Puerto Rico,
Culebra, and the northern U.S. Virgin Islands. A High Rip Current
Risk remains in effect for the western, northern and eastern beaches
of Puerto Rico and Culebra through at least Tuesday afternoon. A
High Surf Advisory is also in effect for the northwestern to
northern coastline of Puerto Rico through late tonight. Beachgoers
are strongly urged to stay out of the water at beaches under these
advisories and to heed all warning flags, posted signs, and
instructions from lifeguards and local officials. Although the High
Surf Advisory is currently in effect through late tonight, an
extension is likely.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Tuesday afternoon for PRZ001-002-
     005-008-010-012.

     High Surf Advisory until 6 AM AST Tuesday for PRZ001-002-005-008-
     010.

     Heat Advisory until 5 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...Small Craft Advisory until 6 PM AST Tuesday for AMZ711.

     Small Craft Advisory from 6 PM this evening to 6 PM AST Tuesday
     for AMZ712-741-742.

&&

$$

SHORT TERM/AVIATION...CVB
LONG TERM....MNG
MARINE/BEACH FORECAST...GRS

NWS SJU Office Area Forecast Discussion