252
FXCA62 TJSJ 020852
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Thu Oct 2 2025

.KEY MESSAGES...

* Warmer conditions will continue today, particularly across the
  urban and coastal areas of Puerto Rico and the U.S. Virgin
  Islands. A Heat Advisory is in effect from 10 AM through 5 PM
  AST. Stay hydrated and avoid prolonged sun exposure.

* Showers and thunderstorms along interior and northern portions
  of Puerto Rico will increase flooding and lightning risk this
  afternoon.

* Once again, occasional passing showers are expected across the
  U.S. Virgin Islands throughout the day.

* A long-period swell will arriving late tonight will deteriorate
  marine and coastal conditions through early next week. Small
  Craft Advisories are in effect from midnight tonight for the
  Atlantic offshore waters and from noon Friday for the Atlantic
  coastal waters and the Mona Passage.


&&

.SHORT TERM... Today through Saturday...

Calm weather conditions prevailed overnight with little to no rain
for the US Virgin Islands and windward locations in PR. Winds were
calm to light and variable, influenced by a land breeze. In general,
skies were mostly clear with some clouds moving through the Virgin
Islands. Nighttime cooling allowed the low temperatures to drop from
the mid- to upper 70s in coastal areas to the mid- to upper 60s
across the mountains.

A col area near the region will continue to promote light
southeasterly winds today and tomorrow. Moisture content is expected
to remain near or below normal through Friday. However, the
available moisture, combined with above-normal expected maximum
temperatures, will result in warm to hot heat indices during the
peak of daily heating this afternoon. Thus, a Heat Advisory is once
again in effect for coastal and urban locations in the US Virgin
Islands and Puerto Rico. Excessive heating, enhanced by local
effects and variations in sea breezes, will result in strong
thunderstorms across the interior and northern regions of PR. This
activity is expected to result in cloud-to-ground lightning, heavy
rain, and strong winds. Due to weak steering winds, expect some
thunderstorms to remain almost stationary, leading to a heightened
risk of flooding in poorly drained areas. Be prepared. These storms
will likely clear by evening, resulting in calm weather. A similar
weather pattern is expected to repeat on Friday.

A long-period north-northwesterly swell will impact the Atlantic
coastline, producing dangerous breaking waves and life-threatening
rip currents starting late Thursday night or early Friday morning.
It`s essential to acknowledge the significant threat this poses to
beachgoers who go to the north-facing beaches in Puerto Rico and the
northern US Virgin Islands. Avoid becoming just another statistic.

For Saturday, a weak tropical wave moving across the Caribbean Sea
and a frontal boundary lingering north of the islands over the
Atlantic Ocean will increase the moisture content somewhat, as well
as the potential for more frequent passing showers followed by
isolated to scattered thunderstorms during the afternoon.

&&

.LONG TERM... Sunday through Thursday...

No major changes were introduced to the long-term forecast. A
transition to an unstable and wetter pattern is still anticipated by
the beginning of the workweek, with gradual improvement by
Wednesday. Global models continue to suggest the approach of an
upper-level trough into the CWA by Sunday night. From the
deterministic guidance of the GFS and ECMWF, the tendency towards
wetter conditions is increasing, as Precipitable Water (PWAT) values
may range between 2.0 and 2.2 inches, above the climatological
normal. The latest model solutions also suggest a rise in relative
humidity content in the low and mid levels as well (> 60 %, up to 80
- 90%) during Monday and Tuesday. In terms of instability, the
presence of this upper feature should bring colder than normal 500
mb temperatures (down to -8 degrees Celsius), favorable for the
development of strong thunderstorms. The latest Galvez-Davison Index
(GDI) tool keeps suggesting the potential of isolated to scattered
thunderstorms across the CWA, higher on Monday and Tuesday. As
mentioned in the previous discussion, winds will become lighter late
Monday night and Tuesday, meaning that theres a high chance of
stationary showers and thunderstorms. Given the expected conditions,
the potential of flooding and lightning will increase, particularly
over mountain ranges and eastern Puerto Rico, including Vieques and
Culebra, and the U.S. Virgin Islands.

Conditions should gradually improve by Wednesday, as a drier air
mass may filter into the region.  Although PWAT may drop to seasonal
values (1.5 - 1.7 inches), the available moisture combined with
diurnal heating and local effects could trigger convection activity
in the afternoon, affecting mainly portions of interior and western
Puerto Rico, including the San Juan Metropolitan Area. Nevertheless,
the likeliest scenario could be mostly ponding of water over
roadways, urban, and poorly drained areas.

The National Hurricane Center is monitoring a tropical wave expected
to move off the coast of Africa in the next few days, with a 20%
chance of cyclonic formation in the next 7 days. The latest model
solutions suggest an increase in moisture content due to this
tropical wave approaching the Caribbean Basin by late Thursday
night, but the variability between them is high, introducing
uncertainty to the forecast. Hence, well keep monitoring the
development of this system.

&&

.AVIATION...

(TAFs 06z)

VFR conditions will prevail today for all TAFs. However, a few TSRA
will develop during the afternoon, between 02/15-22z, which could
impact JSJ or JBQ, creating brief MVFR conditions if those TSRA move
over them. Winds will prevail mainly from the S-SE at 5-10 kt, with
sea breeze variations after 02/13z, and gusty winds near TSRA. Winds
will turn calm to light and VRB aft 02/23z.

&&

.MARINE...

A col near the region will promote a light to gentle southerly wind
flow across the islands through Friday. A long-period north to
northwesterly swell will begin to spread across the local Atlantic
waters late tonight and into Friday, deteriorating marine and coastal
conditions through early next week. Additionally, a weak tropical
wave is expected to move over the Lesser Antilles by Friday, moving
near the islands by Saturday. At the same time, a frontal boundary
will remain positioned to the north over the Atlantic.

&&

.BEACH FORECAST...

No major changes were introduced to the beach forecast. As
anticipated, the rip current risk increased to moderate mainly for
the northern beaches of Puerto Rico, including Culebra. As
mentioned in previous discussions, a long-period swell will arrive
late tonight, bringing hazardous beach conditions through at
least early next week. Life-threatening rip currents are expected
along the north- facing beaches of Puerto Rico, including Vieques
and Culebra, and the northern U.S. Virgin Islands, spreading over
west-facing beaches of Puerto Rico and St. Croix in the U.S.
Virgin Islands during the weekend. Additionally, the potential of
High Surf conditions is increasing due to high chance of breaking
waves above 10 feet. Therefore, citizens and visitors are
encouraged to continue monitoring the beach forecast and heed the
advice of the flag warning system. Regarding the weather forecast,
beachgoers should stay weather alert due to the potential of
showers and thunderstorms near and/or approaching the beach zone,
particularly over the western and northeastern coastal areas of
Puerto Rico.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001>005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...Small Craft Advisory from midnight tonight to 4 AM AST Monday
     for AMZ711.

     Small Craft Advisory from noon Friday to 4 AM AST Monday for
     AMZ712-716-741-742.

&&

$$

SHORT TERM/AVIATION...CAM
LONG TERM...MNG
MARINE/BEACH FORECAST...CAM/MNG