National Weather Service Today's Weather Impact Levels

449
FXCA62 TJSJ 100905
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Wed Dec 10 2025

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

.KEY MESSAGES...
Issued at 440 AM 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(Today through Friday)...
Issued at 440 AM AST Wed Dec 10 2025

Satellite imagery and Caribbean radar data overnight indicated the
leading edge of a trade wind perturbation moving into the local
area. This feature produced brief clusters of showers across the
U.S. Virgin Islands and the southeastern coastal areas of Puerto
Rico, although rainfall totals generally remained under one-tenth of
an inch. The bulk of deeper moisture and shower activity persisted
farther east across the Leeward Islands, coinciding with slightly
higher Advected Layer Precipitable Water (ALPW) values within the
700-500 mb layer.

For today, the mid-level ridge centered northeast of the region will
continue to dominate the overall pattern, while weak troughiness
lingers to the northwest. Instability aloft remains marginal and
characteristic of the season, but a notable increase in low-level
moisture will accompany the advancing perturbation. Model guidance
continues to support precipitable water values fluctuating near or
around 2.0 inches as the disturbance moves across the islands. As a
result, expect an uptick in shower frequency, particularly for
windward coastal areas during the morning hours, followed by
additional afternoon showers developing over the interior and
northwestern Puerto Rico due to diurnal heating and local sea breeze
convergence.

Low-level winds will strengthen and veer slightly southeasterly
through the day, with 925 mb wind speeds forecast to reach above-
normal levels. Breezy conditions along coastal sectors are therefore
likely, with locally higher gusts in showers. A limited flooding
threat remains possible, mainly ponding of water on roads and poor-
drainage areas where showers persist.

For Thursday and Friday, model guidance indicates a broadly similar
pattern, with alternating pockets of drier and moister air moving
through the trade wind flow. These fluctuations in precipitable
water will largely dictate shower coverage from one period to the
next. Overall, mid-level relative humidity is expected to remain on
the lower side, limiting vertical development and keeping most
showers shallow and brief.

During the overnight and morning hours each day, patches of
increased moisture will support passing showers across windward
coastal areas. As drier slots move in, activity will diminish,
especially through the mid-day period. Isolated afternoon showers
may still form across the interior and western Puerto Rico due to
diurnal heating and sea breeze convergence, but rainfall
accumulations should remain light given the persistent mid-level
dryness. Breezy east-southeasterly winds will continue, particularly
along coastal sectors, with no significant flooding threat
anticipated.

&&

.Long Term(Saturday through Wednesday)...
Issued at 440 AM 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...
(06Z TAFS)
Issued at 440 AM AST Wed Dec 10 2025

Mainly VFR across all terminals. A trade-wind perturbation will
bring periods of -SHRA/VCSH moving in from the E, mainly affecting
USVI terminals (TIST/TISX) and occasionally TJSJ through the
morning. Brief MVFR CIGS/VIS possible in passing SHRA. Low-level
winds ESE-SE 1016 kt, with ocnl higher gusts aft 14Z. Sea-breeze
influences after 14Z may trigger SHRA/VCSH over TJBQ and interior PR
terminals.

&&

.MARINE...
Issued at 440 AM 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 440 AM 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/AVIATION...CVB
LONG TERM/MARINE...MNG

NWS SJU Office Area Forecast Discussion