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FXCA62 TJSJ 161710
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
110 PM AST Thu Oct 16 2025

.KEY MESSAGES...

* For Puerto Rico, there is a limited to elevated flood threat,
  with the heaviest showers expected along the eastern sections
  through Saturday. Another band of thunderstorms from the
  Atlantic waters could move tonight from the northwest to
  northeast coast.

* For the U.S. Virgin Islands, shower and thunderstorm activity is
  expected to increase from Friday through Saturday.

* A gradual improvement in weather conditions is forecast by late
  Monday as a drier airmass moves across the islands.

* Northerly swells will lead to deteriorating seas and life-
  threatening rip currents from Friday into early next week.
  Small craft advisories, rip current/high surf/coastal flood
  statements will be required, particularly from Sunday through
  Tuesday.


&&

.SHORT TERM...Rest of today through Saturday...

Mostly sunny to partly cloudy skies were observed during the
morning hours across the islands after a rainy early morning
across Puerto Rico. As of 1 PM AST, high temperatures were from
the upper 80s to low 90s across most coastal areas with heat
indices up to 105F in general. The wind was from the west to
southwest between 6 to 14 mph.

A frontal system over the Atlantic waters will linger over the
local area through the short-term period. This will promote normal
to above-normal precipitable water content between 1.80-2.20
inches. Meanwhile, a polar trough will also promote colder than
normal 500 mb temperatures of near -8C, which will support
thunderstorm development each day. The flood threat will remain
elevated mainly for portions of the Cordillera and the eastern
half of PR. However, another band of showers and thunderstorms
could move once again from the northwest to northeast coast of PR
tonight, leading to brief periods of heavy rainfall and strong
gusty winds. Across the USVI, the wettest period is expected from
late Friday into Saturday morning.


.LONG TERM...Sunday through Wednesday...

/From prev discussion issued at 532 AM AST Thu Oct 16 2025

Wet and unstable weather conditions are expected to persist through at
least Monday as the remnants of a frontal boundary and its
associated moisture continue to influence the local area. This
pattern will result in increased moisture and instability,
supporting periods of showers and thunderstorm activity across the
region. The latest model guidance indicates deep-layer moisture
extending from the surface to the mid-levels, maintaining a moist
environment favorable for convection. As a result, frequent
showers and thunderstorms are expected, with activity affecting
mainly the windward and coastal sections during the nighttime and
early morning hours, and developing across the interior and
western portions of Puerto Rico during the afternoon hours. Given
the abundant moisture and instability, lightning and localized
flooding threats will range from limited to elevated, particularly
across portions of Puerto Rico through Monday.

By late Monday, a gradual improvement in weather conditions is expected
as drier air filters into the region. For Tuesday and Wednesday,
weather conditions should become more stable overall, with
moisture levels fluctuating around seasonal to below values for
this time of the year. Despite the drying trend, residual moisture
and local effects combined with daytime heating will still
promote isolated to scattered afternoon showers, mainly over the
interior and western Puerto Rico. The flooding threat during this
period should remain limited to none.

However, by the later part of the workweek, model guidance shows a
gradual increase in moisture and shower activity as a tropical
wave or potential tropical system moves south of the region. Until
then, fair weather and limited convection are expected, with
isolated afternoon showers possible over the western interior due
to local and diurnal effects.

We urge citizens and visitors to continue to monitor the forecast
for any significant changes.


&&

.AVIATION...

(18Z TAFS)

TEMPO MVFR conds possible at TJSJ/TIST/TISX thru 16/23z due to
SHRA/TSRA. A lingering frontal system over the Atlantic waters
will continue to produce strong thunderstorms over the local waters,
and under westerly steering winds this can lead to intermittent
periods of SHRA/TSRA once again tonight at TJBQ/TJSJ. The 16/12z
TJSJ sounding indicated WSW winds at 8-14 kt blo kt blo 3000ft.


&&

.MARINE...

A frontal system over the Atlantic offshore waters will continue
to produce showers and thunderstorms across the regional waters
through the weekend. Light southwesterly winds are expected during
this period. Pulses of a long period northerly swell will reach
the Atlantic waters and passages from Friday into early next week.
Hazardous seas building up to 8 feet are expected from late
Sunday into Monday, triggering Small Craft Advisory conditions
across the Atlantic waters and Caribbean Passages through midweek.
Moderate to locally fresh easterly winds will return from Sunday
onward.


&&

.BEACH FORECAST...

Pulses of long period northerly swells will gradually increase the
threat of life-threatening rip currents along the west, north,
and eastern beaches of the islands during the next few days. High
surf conditions and minor coastal flooding are likely on Sunday
and Monday as the northerly swell builds seas between 6 and 8 feet
around 12 to 14 seconds, which translates to breaking waves between
10 and 15 feet. Dangerous swimming conditions, minor beach
erosion, and life-threatening rip currents are expected from this
weekend into early next week.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

DSR/MNG