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651
FXCA62 TJSJ 190905
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Fri Dec 19 2025

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

.KEY MESSAGES...
Issued at 500 AM AST Fri Dec 19 2025

* Life-threatening rip currents will prevail across the northern
  exposed beaches of Puerto Rico and Culebra through this
  afternoon. Moderate risk across the U.S. Virgin Islands.

* Another northerly swell and increasing trade winds will cause
  hazardous seas and life-threatening rip currents to redevelop
  from Saturday afternoon through Sunday.

* Isolated showers this morning across windward portion of Puerto
  Rico and the U.S. Virgin Islands, then drier air will limit
  rainfall and promote stable conditions most of the day, with
  localized afternoon showers developing across western Puerto
  Rico.

* Cooler temperatures and better rain chances are anticipated
  around mid-week next week due to an approaching frontal boundary
  and better dynamics aloft.

&&

.Short Term(Today through Sunday)...
Issued at 500 AM AST Fri Dec 19 2025

A surge of moisture brought scattered to widespread passing showers
across the local waters, the US Virgin Islands, and the windward
locations in Puerto Rico. This activity results in periods of
moderate to locally heavy rain. Meanwhile, the leeward portions of
PR had calm weather conditions, with mostly clear to partly cloudy
skies overnight. Most of the activity moved out of the USVI region
around 2 AM AST, leaving mostly clear skies early this morning. The
winds were mainly from the northeast, influenced by land breeze
variations. Minimum temperatures ranged from the low to mid-70s
along the coast to the low-60s in the mountains and valleys.

As the overnight surge of moisture exits the region, there is a high
likelihood (70-80%) that a drier air mass will advect into the
islands from the east. This drier air, interacting with a mid- to
upper-level ridge aloft, will very likely (>70%) suppress deep
convection and limit rainfall coverage across Puerto Rico and the
U.S. Virgin Islands through at least Saturday. Overall, a stable
weather pattern is likely to persist (60-80%) through Saturday.

By Sunday, model guidance indicates a moderate to slightly high
confidence (50-60%) that the mid-level ridge will weaken, allowing
moisture to increase into the mid-levels and marginally enhance
atmospheric instability across the region.

Under this pattern, the probability of rainfall today and Saturday
will generally range from low (0-20%) to moderate (30-50%). With
east-northeasterly winds persisting, the highest likelihood of
passing showers will remain over windward areas of Puerto Rico and
the U.S. Virgin Islands during the early morning and evening hours,
while interior and western Puerto Rico will have a low to moderate
chance (20-40%) of afternoon showers driven by local and sea-breeze
effects.

From late Saturday night into early Sunday morning, the probability
of rainfall is expected to increase from moderate (30-50%) to high
(60-70%), as weakening ridging aloft and a surface-level perturbation
enhance low- to mid-level moisture availability. As a result, the
flooding risk is likely to increase from none to limited during
this period. Under a limited risk scenario, frequent periods of
moderate to locally heavy rainfall could lead to ponding of water
on roads and in poorly drained areas, with a low probability of
isolated urban and small-stream flooding.

&&

.Long Term(Monday through Friday)...
Issued at 500 AM AST Fri Dec 19 2025

Early next week, mid level ridging will gradually weaken as a
polar trough exiting the eastern United States advances from the
northwest. Surface high pressure building across the western
Atlantic will promote persistent northeast flow across the region
while a frontal boundary is pushed into the central Atlantic.
Patches of low level moisture will continue to move across the
area, resulting in isolated to scattered showers over windward
sections of Puerto Rico and the U.S. Virgin Islands, mainly during
the night and morning hours. By late morning into the afternoon,
a moderate chance of scattered showers, around 50 percent, is
expected across interior and western Puerto Rico, posing a limited
flood risk on Monday and Tuesday.

From Tuesday onward, atmospheric instability will increase as 500
mb temperatures cool to below normal values between -7 and -10
degrees Celsius. Rain chances will increase, with probabilities
rising to 50 to 60 percent for scattered to numerous showers.A
polar trough will extend southward into the Caribbean, while an
additional upper-level trough will interact with a surface frontal
boundary across the region. The frontal boundary will linger
close to the area, allowing moisture to pool across the region,
while enhanced upper-level divergence and atmospheric instability
will support rising motion. As a result, unsettled weather
conditions will develop,, particularly from Wednesday through
Friday, with increasing cloudiness, showers, and isolated
thunderstorms expected across parts of the Caribbean.

As the frontal boundary approaches and lingers to the north of the
region, precipitable water values will increase to between 1.5 and
1.8 inches, within the seasonal to above normal range. Model
guidance, including the Galvez Davison Index, supports the
potential for shallow convection with isolated thunderstorm
development. Periods of locally heavy rainfall may lead to
localized flooding in flood prone and poorly drained areas,
including roadway ponding. At this time, flood risk ranges from
limited to elevated for portions of Puerto Rico, particularly
across the northeastern sectors. Cooler temperatures are expected
during the holiday period, as indicated by a trend toward below
normal 925 mb temperatures.

&&

.AVIATION...
(06Z TAFS)
Issued at 500 AM AST Fri Dec 19 2025

VFR conditions will prevail through much of the forecast period,
without ruling out a few passing showers near or across JSJ/IST/ISX.
SHRA/-SHRA will then form over the interior and western PR (near
JBQ) between 19/17-23z. Winds will be calm to light and variable
through this morning, then return from the ENE after 19/13z at 10-
15kt with higher gusts and sea breeze variations.

&&

.MARINE...
Issued at 500 AM AST Fri Dec 19 2025

Moderate to locally fresh east to northeast winds will continue
across the local waters today. A Small Craft Advisory (SCA) remains
in effect through midday today for the offshore Atlantic waters, due
to hazardous marine conditions for small craft operators. Seas are
expected to briefly subside this afternoon through early Saturday.
However, another long-period northerly swell, generated by a surface
low over the central Atlantic, will spread across the local Atlantic
waters and Caribbean passages, causing hazardous marine conditions to
redevelop and SCA conditions to return Saturday afternoon into Sunday.

&&

.BEACH FORECAST...
Issued at 500 AM AST Fri Dec 19 2025

A High Risk of rip currents continues through this afternoon along
the north-facing beaches of Puerto Rico and Culebra. Dangerous rip
currents are likely within the surf zone, and beachgoers are urged
to strictly follow guidance from lifeguards, beach patrol flags,
and posted signs. Tonight, the risk is expected to decrease to
moderate for most beaches through Saturday night, while low risk
conditions will prevail along the southern beaches of the islands.
Remember, a moderate risk means that life-threatening rip currents
are possible, and even during low risk conditions, dangerous rip
currents can still occur, especially near groins, jetties, reefs,
and piers.

By late Saturday into Sunday, beach conditions are forecast to
deteriorate again as strengthening winds and another northerly
swell spread across the local Atlantic waters, leading to large
breaking waves. Stay tuned to the forecast and exercise caution at
the beaches.

&&

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

VI...None.
AM...Small Craft Advisory until noon AST today for AMZ711.

     Small Craft Advisory from noon Saturday to noon AST Sunday for
     AMZ711.

&&

$$

SHORT TERM/AVIATION...CAM
LONG TERM/MARINE/BEACH...YZR

NWS SJU Office Area Forecast Discussion