451
FXCA62 TJSJ 101741
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
Issued by National Weather Service Brownsville TX
141 PM AST Wed Dec 10 2025

...New SHORT TERM, AVIATION...

.KEY MESSAGES...
Issued at 133 PM AST Wed Dec 10 2025

* Marine and beach conditions will deteriorate beginning Thursday.
  Expect choppy to rough seas and life-threatening rip currents.

* Breezy to windy conditions are anticipated today across coastal
  and elevated areas. Light-weight outdoor items may be blown
  around in exposed locations.

* For Puerto Rico, shower activity will increase throughout the
  day, with limited flooding risk over eastern portions during the
  morning and the northwestern section in the afternoon.

* For the U.S. Virgin Islands, showers will become more frequent
  today, promoting ponding of water over roadways and poorly
  drained areas.

&&

.Short Term(This evening through Friday)...
Issued at 133 PM AST Wed Dec 10 2025

The latest radar and satellite imagery reveal ongoing light to
moderate showers and associated cloud cover translating east in
response to a trade wind perturbation. Overall rainfall amounts
are expected to remain light as the highest moisture content
remains further east, but pockets of brief, locally heavy rainfall
cannot be ruled out, especially as the aforementioned
perturbation interacts with diurnal instability and the local sea
breeze. This may result in ponding of water on roadways or low-
lying, flood-prone areas. Otherwise, expect occasional wind gusts
around 20-25 MPH through the afternoon hours and early evening
hours, mainly across the east-facing coast and eastern islands.
These gusts should begin to subside later this evening and
overnight over Puerto Rico, generally below 10 MPH.

Through the end of the week, similar conditions are expected as
fluctuations in precipitable water values, diurnal instability,
and the influence of the local sea breeze allow for isolated to
scattered showers through Friday. No significant flooding threat
is expected as rainfall amounts should remain light give the
shallow nature of the moisture content in the lower levels.
Easterly to southeasterly winds should remain fairly light,
generally around or below 10 MPH over Puerto Rico, with elevated
winds over the waters and eastern islands.

&&

.LONG TERM(Saturday through Wednesday)...
Issued at 133 PM AST Wed Dec 10 2025

Variable conditions may persist early next week, introducing changes
to the long-term forecast. The surface high pressure lingering over
the Central Atlantic will continue to promote southeasterly winds,
bringing breezy to windy conditions on Saturday. Due to the presence
of the mid-level ridge lingering northeast of the region, shower
activity should remain limited.  But conditions will slightly worsen
as a disturbance in the trades is now expected to arrive late
Saturday night into Sunday, increasing the frequency of showers
across the windward sections of the islands. From the latest
probabilistic guidance of the GFS and the ECMWF, ensemble members
are now tending to a wetter pattern for this time of the year, as
there is a medium chance of seasonal and above climatological normal
Precipitable Water (PWAT) values (1.4 - 1.6 inches), with a low
chance of reaching 2.0 inches. By late Sunday night, the moisture
content should decrease and remain between 1.2 and 1.4 inches.
Although the frequency of showers should decrease, the latest
guidance suggests that the surface high pressure will interact with
a polar trough, weakening the pressure gradient. Winds should
become light and variable by Monday and Tuesday, meaning any
developing shower will likely become stationary and produce higher
rainfall accumulations. The latest model solutions show the polar
trough deepening more into the tropics, cooling 500 mb
temperatures (around -7 degrees Celsius), and enhancing marginal
instability conditions. Additionally, an
upper level trough may weaken the mid-level ridge and increase
instability aloft. Although the lightning risk is not expected to
be widespread, the chance of short-lived isolated thunderstorms
is increasing. Overall, afternoon convection is expected each day
of the period, with flooding potential increasing on Monday and
Tuesday, particularly over portions of western/northwestern Puerto
Rico and the San Juan Metropolitan Area. Although the flooding
risk is not anticipated across the U.S. Virgin Islands, streamers
developing near noon may linger near the coastal areas.

With southeasterly winds expected through most of the period, warmer
than normal temperatures will continue across the islands, with very
localized areas reaching 100 degrees Fahrenheit heat indexes during
daytime. Nevertheless, no heat risk is expected across the islands
for the rest of the forecast period.

&&

.AVIATION...
(18Z TAFS)
Issued at 133 PM AST Wed Dec 10 2025

Periods of SHRA/VCSH will continue through the early evening hours
in response to a trade wind perturbation that is translating
across the region. Brief periods of MVFR ceilings and visibility
cannot be ruled out within any robust showers. Expect easterly to
southeasterly winds around 10-15 knots, with occasional higher
gusts through the afternoon hours. Winds will fall below 10 knots
overnight at TJBQ, TJPS, and TJSJ, but will remain elevated at
TIST and TISX.

&&

.MARINE...
Issued at 133 PM AST Wed Dec 10 2025

A building surface high pressure over the Central Atlantic will
continue to promote easterly gentle to moderate winds today,
becoming moderate to locally fresh tonight. Increasing winds
combined with a long- period northerly swell arriving early Thursday
will lead to choppy to rough seas mainly over the Atlantic offshore
waters. A Small Craft Advisory in effect from Thursday morning
through late Thursday night. Although conditions will slightly
improve by Friday, hazardous conditions for small craft may return
by the weekend.

&&

.BEACH FORECAST...
Issued at 133 PM AST Wed Dec 10 2025

Today, the rip current risk will remain moderate along the north
and east-facing beach of Puerto Rico, including Vieques and
Culebra, and the U.S. Virgin Islands. Although the risk is
moderate, beachgoers are encouraged to exercise caution as life-
threatening rip current are possible along the surf zone.

The forecast remains on track, as increasing winds combined with a
northerly long- period swell arriving early tomorrow will
increase breaking wave along exposed beaches and bring hazardous
beach conditions. Hence, a high risk of rip currents is
anticipated along the northern beaches of Puerto Rico and the U.S.
Virgin Islands. As the swell spreads and diminishes by Friday,
dangerous beach conditions may persist in the weekend. Residents
and visitors are are urged to check the beach forecast before
going out, and heed the advice of the flag warning system.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory from 6 AM Thursday to 6 AM AST Friday for
     AMZ711.

&&

$$

SHORT TERM...Garcia/BRO
LONG TERM....MNG
AVIATION...Garcia/BRO

NWS SJU Office Area Forecast Discussion