948
FXCA62 TJSJ 051638
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1238 PM AST Fri Dec 5 2025

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

.KEY MESSAGES...
Issued at 1238 PM AST Fri Dec 5 2025

 * Pleasant conditions will persist for the rest of the day and
   night hours, although with increasing showers in the overnight
   and end of the day.

 * Temperatures will be seasonably warm during the days, and mild
   to cool during the nights. Highs will reach the 80s in the
   coastal area, and the 70s in the mountains. Lows will be from
   the low 60s to low 70s.

 * The Virgin Islands will also experience fair weather, with
   rainfall interruptions at times, mostly in the night and early
   morning hours.


&&

.Short Term(This evening through Sunday)...
Issued at 1238 PM AST Fri Dec 5 2025

Mostly sunny skies prevailed for most of the day, with only a few
passing showers reaching the islands at times. Enough sunshine
allowed for temperature to climb to the mid and upper 80s in
portions of Puerto Rico and the Virgin Islands. It was much cooler
in the mountains, with highs below 80s degrees. A few showers may
manage to form this afternoon along western Puerto Rico, but the
flooding threat is very low to none.

The most recent satellite imagery shows a drier air mass moving
over the islands, with precipitable water values of 1.1-1.2
inches. This is even lower that what TJSJ 05/12z sounding showed
this morning. At the mid and upper level, a ridge is holding just
west of the local islands, with a trade wind cap evident around
850 mb. This environment does not favor the formation of any
strong showers nor thunderstorms, since any available moisture
will be trapped closer to the surface. A surface high pressure
will also maintain the gradient tight, with breezy conditions
anticipated. Even though the atmosphere will not favor strong
showers, these stronger winds will drag patches of moisture from
the Atlantic into the northeastern Caribbean. A few late evening
and early morning showers can be anticipated for the Virgin
Islands and eastern Puerto Rico, followed by limited convection
along western Puerto Rico. Again, the risk of flooding will be
very low to none with this activity.

&&

.Long Term(Monday through next Thursday)...
Issued at 1238 PM AST Fri Dec 5 2025

The long-term forecast remains on track under a favorable stable
weather column across the islands. A strong and stalled mid to
upper-level ridge expanding in the central Atlantic will be the
main weather feature during the period.These features will hold a
stable weather pattern with warmer conditions aloft and a strong
trade wind cap inversion that limits vertical development across
the islands. Under this pattern, and as suggested by the 500 MB
temperatures in the -5 degrees, thunderstorm activity is not
anticipated. Although a lightning threat is not forecasted,
diurnal heating can still induce short-lived thunderstorms. Although
very stable conditions will prevail, a strong surface high
pressure over the Central Atlantic will drag patches of trapped
moisture at 850 MB. According to the global model guidance,
patches of trapped moisture with precipitable water values from
1.4 to 1.6 inches, close to the climatological normals, will move
in and out of the region embedded in the trade winds. Therefore,
in the afternoon, brief passing showers are possible due to
diurnal heating and local effects. Surface winds will remain
mostly from the east as the surface high pressure remains in the
Central Atlantic, and veering winds are forecast from Monday
onwards as the surface high pressure builds further into the
Central and Eastern Atlantic.

By midweek, as the surface high pressure establishes across the
central Atlantic, a tight in the pressure gradient will result in
breezy conditions. Additionally, since the surface winds will
remain east-southeasterly and plenty of sunshine will be present
due to the lack of instability, daytime temperatures will remain
just slightly above seasonal levels across the islands. According
to the global model guidance, 925 MB temperatures suggest warmer
conditions from Monday onwards, with Tuesday the warmest day of
the long term.

&&

.AVIATION...
(18Z TAFS)
Issued at 1238 PM AST Fri Dec 5 2025

Mostly VFR conditions expected to prevail through the forecast
period. Passing SHRA expected in the vicinity of USVI after 00Z,
but impacts to operations, if any, are expected to be minimal.
Winds will be from the E at 10-15 kts, and stronger gusts before
00Z, calming down to below 10 knots until 05/13/14z.

&&


&&

.MARINE...
Issued at 1238 PM AST Fri Dec 5 2025/prev discussion/

Today, an extending surface high pressure will dominate the
islands, producing moderate easterly winds and seas reaching up to
5 feet. A drier air mass is also moving across the region, which
will limit shower activity throughout the day. Global model
guidance indicates that energy from an incoming northerly swell
will reach the northern offshore Atlantic waters, likely leading
to higher seas and hazardous marine conditions. An increase in
surface winds will result in wind-driven seas, and energy from a
north-northwesterly swell will increase seas across the Atlantic
waters and the local passages.

&&


.BEACH FORECAST...
Issued at 1238 PM AST Fri Dec 5 2025

Increasing winds will lead to a moderate rip current risk through
much of the period. These conditions will persist through much of
the weekend and early next week. Winds will pick up further by
mid-week, likely triggering a high rip current risk.

&&

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

$$

SHORT TERM/AVIATION...ERG
PUBLIC DESK....RVT