775
FXCA62 TJSJ 081658
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1258 PM AST Mon Dec 8 2025

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

.KEY MESSAGES...
Issued at 1225 PM AST Mon Dec 8 2025

* Marine and beach conditions will deteriorate by the second part
  of the workweek due to the combination of a long period
  northerly swell and increasing winds. Expect choppy to rough
  seas and life-threatening rip currents.

* Winds will increase late in the week, leading to breezy to windy
  conditions across coastal and elevated areas by midweek.
  Lightweight outdoor items may be blown around in exposed
  locations.

* For Puerto Rico, showers are expected during the night and
  early morning hours across the east/southeastern portions. Over
  west/northwest PR, afternoon showers are expected each day.

* For the U.S. Virgin Islands, passing showers are very likely
  during the nights and early morning hours.

&&

.Short Term(This evening through Wednesday)...
Issued at 1225 PM AST Mon Dec 8 2025

Mostly sunny skies were observed during the morning hours across
Puerto Rico and the U.S. Virgin Islands. Partly cloudy skies were
observed early in the afternoon hours over the USVI. Little to no
rainfall activity was detected over land areas during the day, but
showers are expected to increase over portions of the islands this
afternoon. Maximum temperatures were in the low 90s across the
northern coast of PR, and in the upper 80s across the rest of the
coastal areas of the islands. The wind was from the southeast
between 10 and 15 mph with sea breeze variations along the
northern coast of PR.

For the rest of the short-term period, a mid-to upper-level ridge
will continue to build just northeast of the local area, providing
somewhat stable conditions aloft. However, today was the driest
day of the period, as a weak upper level trough pressing over the
ridge will create some weakness west of the region. This will
allow for columnar moisture to increase gradually during the next
few days, but particularly on Wednesday, when precipitable water
content is expected to peak just under 2 inches, which is above
seasonal levels. Winds will turn more southeasterly as the surface
high pressure continues to gradually build over the Azores late
in the period. Moisture content is expected to peak each night,
favoring shower activity over the windward areas of the islands,
with afternoon showers expected each day over west/northwest PR.
On Wednesday, there will be more moisture content and somewhat
higher instability than previous days. This could lead to
possible isolated thunderstorm development over western PR in the
afternoon.

&&

.Long Term(Thursday through next Sunday)...
Issued at 357 AM AST Mon Dec 8 2025

No major changes were introduced to the forecast, as a broad mid-
level ridge will dominate and promote mostly fair conditions and
limited rainfall across the CWA. Moisture content will vary at
times, as a broad surface high pressure moving over the Central
Atlantic will bring patches of moisture, increasing the frequency of
showers across the islands. Based on the deterministic guidance of
the GFS and ECMWF, PWAT values will likely remain below normal
(between 1.2 and 1.4 inches), with a low chance of near above
climatological normal (up to 1.6 inches). Additionally, mid-level
moisture RH is expected to plummet well below normal (down to 10%)
while low to mid-level lapse rates shall remain seasonal to below
normal (3 - 5 degrees Celsius per kilometer). In terms of
instability, deep convection activity may be limited as 500 mb
temperatures will likely be warmer than normal (between -5 and -6
degrees Celsius), as the presence of the mid-level ridge should
promote stability aloft. A seasonal weather pattern is very likely
over the period, with passing showers moving over windward
sections and the U.S. Virgin Island streamers by noon, while
daytime heating combined with local effects and available moisture
should be enough for afternoon convection each day, particularly
over the western and northwestern portions of Puerto Rico. Due to
increasing winds, likely to promote breezy to locally windy
conditions, showers should become more progressive and less
stationary, reducing the chance of flooding. Although a lightning
risk is not expected through the period, short-lived isolated
thunderstorms cannot be ruled out, particularly by the end of the
period.

Under a southeasterly wind flow, warmer-than-normal temperatures are
expected throughout the period, particularly during the day.
Although isolated areas may reach heat indexes of 100 degrees
Fahrenheit at low elevations on the islands, no heat threat is
expected in the long-term forecast.

&&

.AVIATION...
(18Z TAFS)
Issued at 1225 PM AST Mon Dec 8 2025

Mainly VFR conditions expected across all terminals during the
next 24 hours. However, -shra en route from the Windward Islands
could move tonight over the USVI terminals. This may lead to brief
MVFR cigs at TISX. The 08/12z TJSJ sounding indicated ESE winds up
to 21 kt blo FL050.

&&

.MARINE...
Issued at 1225 PM AST Mon Dec 8 2025

A broad surface high pressure over the Central Atlantic will promote
east to southeast moderate to locally fresh winds today, weakening
and becoming moderate tonight. By midweek, strengthening surface
high pressure north of the region will tighten the pressure gradient
and increase winds, allowing seas to build across the Atlantic waters
and exposed passages. Additionally, a long-period northerly swell
arriving late Thursday night will further worsen conditions. Choppy
to rough seas are expected, with Small Craft Advisories likely by the
end of the workweek. A gradual improvement remains possible by the
weekend as winds and swell ease.

&&

.BEACH FORECAST...
Issued at 1225 PM AST Mon Dec 8 2025

A moderare risk of rip currents will persist through at least
Wednesday across most east/north facing beaches of the islands.
The risk of life-threatening rip currents will increase from
Thursday into the weekend due to the combination of a northerly
long period swell and increasing wind-driven waves from the east.
High Surf Advisories and Rip Current Statements will likely be
issued for portions of the islands during that period.

&&

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

$$

SHORT TERM...DSR
LONG TERM/MARINE...MNG
BEACH/AVIATION...DSR