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182
FXCA62 TJSJ 260753
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
353 AM AST Mon Oct 26 2026

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

.KEY MESSAGES...
Issued at 353 AM AST Mon Oct 26 2026

* A Heat Advisory is in effect today for Puerto Rico and the U.S.
  Virgin Islands. Hot, humid conditions will increase the risk of
  heat-related illness, particularly in coastal and urban areas.
  Elevated heat impacts will persist Tuesday before easing
  Wednesday.

* Life-threatening rip currents will affect exposed beaches
  through Wednesday, particularly along northern, northwestern,
  and eastern Puerto Rico, Culebra, and portions of the northern
  U.S. Virgin Islands.

* Repeated showers this afternoon and tonight could produce urban
  and small stream flooding and isolated flash flooding across
  southern Puerto Rico. A more limited flooding threat will affect
  eastern Puerto Rico and the southern slopes, with isolated
  thunderstorms bringing lightning and gusty winds.

* Hazardous seas will also affect small craft today and Tuesday.
  Rainfall coverage should decrease Wednesday and Thursday as
  drier air arrives.

* The ECMWF indicates greater drying than the GFS, limiting
  confidence in how much the pattern improves. Increasing moisture
  and cooler temperatures aloft could support renewed heavy
  showers and thunderstorms Friday into Saturday, increasing the
  potential for localized flooding.


&&

.Short Term(Today through Wednesday)...
Issued at 353 AM AST Mon Oct 26 2026

Mostly clear to partly cloudy skies prevailed overnight.
Temperatures stayed above typical October lows across much of the
region, with readings since midnight generally in the lower to
mid-80s in coastal and urban areas and the U.S. Virgin Islands,
and in interior Puerto Rico in the mid-60s to 70s. Southerly flow
carried showers from the local waters into windward areas, mainly
along southern Puerto Rico, producing periods of moderate to
locally heavy rainfall.

The unusually warm start will cause temperatures to rise quickly
this morning, with hot, humid conditions increasing the risk of
heat-related illness, particularly across coastal and urban areas
of Puerto Rico and the U.S. Virgin Islands. A Heat Advisory is in
effect for the region. Southeasterly flow will carry showers into
windward areas today and tonight as moisture increases. The
flooding threat will be greatest across southern Puerto Rico,
where persistent or repeated showers could produce urban and small
stream flooding and isolated flash flooding. Elsewhere across
southern slopes and eastern Puerto Rico, heavier showers could
cause ponding on roads and in poorly drained areas. A ridge at mid
and upper levels, warm temperatures aloft, and relatively dry
midlevels will limit deep convection. Nevertheless, daytime
heating, sea breeze convergence, and terrain effects will support
isolated afternoon thunderstorms, bringing lightning and brief
gusty winds.

Puerto Rico and the U.S. Virgin Islands will remain between a
trough over the western Caribbean and a ridge over the eastern
Caribbean through Tuesday. Southerly to southeasterly flow will
transport tropical moisture across the region, while warm
surrounding waters help maintain a moist boundary layer. Local
convergence, daytime heating, and terrain effects will support
additional rounds of showers, particularly Tuesday afternoon into
the overnight hours. The flooding threat will remain limited, with
heavier or repeated showers producing ponding on roads and in
poorly drained areas, as well as isolated urban and small-stream
flooding, mainly across eastern and northwestern Puerto Rico and
portions of Vieques.

On Wednesday, both GFS and ECMWF guidance indicate decreasing
moisture, although they differ on the extent of drying. The GFS
keeps precipitable water near 1.8 to 2.0 inches, while the ECMWF
lowers it to 1.3 to 1.5 inches, below typical October values. Both
models maintain warm temperatures aloft and relatively weak lapse
rates, limiting widespread thunderstorms. Lingering moisture and
local convergence will still support localized showers, but the
ECMWF solution would favor substantially less rainfall. Above-
normal temperatures at low levels will keep conditions warm and
humid, particularly across coastal and urban areas.

Above-normal temperatures and humid conditions will keep heat risk
elevated Tuesday, particularly across coastal and urban areas.
Some relief is expected Wednesday as drier air arrives, although
heat-sensitive individuals and those outdoors without adequate
cooling or hydration will remain at risk.

&&

.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...
(06Z TAFS)
Issued at 353 AM AST Mon Oct 26 2026

Mainly VFR conditions will prevail outside SHRA/TSRA. SE flow will
carry SHRA across USVI and southern and eastern PR terminals today
and tonight. Heavier SHRA may produce brief MVFR conditions and
mountain obscuration btwn 26/15-22z. Local convergence may support
isolated afternoon TSRA across PR. Isolated TSRA could bring
lightning, gusty winds, and locally reduced visibility. SE winds
will prevail at 5-15kt, with daytime sea breeze variations and
higher gusts near SHRA.

&&

.MARINE...
Issued at 353 AM AST Mon Oct 26 2026

A 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 passages today, building seas
between 6 to 8 feet through Tuesday. Small craft advisories will be
in effect for the Atlantic waters and the Mona Passage starting
later today. Isolated thunderstorms are expected to develop mainly
over the Caribbean waters, the Mona Passage, and offshore Atlantic
waters during the next few days.
&&

.BEACH FORECAST...
Issued at 353 AM AST Mon Oct 26 2026

A long period northerly swell will arrive today, with additional
pulses expected through midweek. This swell could generate breaking
waves between 6 and 12 feet, that will cause rough surf and life-
threatening rip currents, mainly along the north facing beaches of
Puerto Rico, Culebra, and the northern U.S. Virgin Islands. A High
Rip Current Risk remains in effect for the northern, western, and
eastern beaches of PR and Culebra through at least Tuesday. High
surf advisory conditions are possible from late today and Tuesday.
Beachgoers are strongly urged to avoid entering the water at beaches
under the high rip current risk. Heed all beach signs/flags and
instructions from lifeguards and local authorities.

&&

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

     Heat Advisory from 9 AM this morning to 5 PM AST this afternoon
     for PRZ001>013.

VI...Heat Advisory from 9 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...Small Craft Advisory from noon today to 6 PM AST Tuesday for
     AMZ711.

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

&&

$$

KEY MESSAGES/SHORT TERM/AVIATION...CAM
LONG TERM....MNG
MARINE/BEACH FORECAST...DS

NWS SJU Office Area Forecast Discussion