872
FXCA62 TJSJ 301714
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
114 PM AST Tue Dec 30 2025

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

.KEY MESSAGES...
Issued at 115 PM AST Tue Dec 30 2025

* The risk of lightning and localized flooding will increase from
  New Year`s Eve into Thursday as an upper-level trough and
  associated frontal boundary approach from the west.

* For the U.S. Virgin Islands, although the approaching upper-
  level trough is expected to increase the chance of showers and
  thunderstorms across the forecast area, organized convective
  activity is expected to remain well west of the USVI.

* Life-threatening rip currents will continue to prevail across
  the north-facing beaches of Puerto Rico, Culebra, and the
  northern U.S. Virgin Islands.

&&

.Short Term(This afternoon through Thursday)...
Issued at 115 PM AST Tue Dec 30 2025

The short-term forecast remains on track, with the chance of
showers and thunderstorms increasing by the end of the period
(Wednesday into Thursday) as an upper-level trough and its
associated frontal boundary approach from the west. As this
feature moves closer to the forecast area, falling heights,
decreasing mid-level temperatures, and increasing moisture
advection are expected, with precipitable water values reaching up
to 2.0 inches. Despite this scenario, the latest guidance
continues to suggest that the highest moisture content and
organized convective activity remain west of the forecast area.

As a result, under this evolving pattern, limited shower activity
is expected to continue, with isolated passing showers across
the north and east coastal areas of Puerto Rico, and the US Virgin
Islands tonight and Wednesday morning. By Wednesday afternoon,
showers will develop over the western interior of Puerto Rico,
with limited shower activity elsewhere. An isolated thunderstorm
cannot be ruled out across western areas tomorrow afternoon.

The chance for showers and thunderstorms will increase Wednesday
night into Thursday, with showers and isolated thunderstorms
reaching the regional waters, particularly the Mona Passage and
Atlantic waters. Some of these showers may reach the western half
of Puerto Rico. Under an east-southeast wind flow, passing showers
are also expected across the eastern coastal areas of Puerto Rico
and the U.S. Virgin Islands. By Thursday afternoon, if breaks in
cloud cover develop, afternoon convection is expected in northwest
Puerto Rico. Therefore, there is an increasing risk of lightning
and minor flooding across the forecast area on Wednesday and
Thursday.

Pleasant temperatures will continue to prevail. At lower elevations,
maximum temperatures are expected to range from the low to
mid-80s, while minimum temperatures are expected to range from the
upper 60s to the low 70s.

&&

.Long Term (Friday through next Tuesday)...
Issued at 401 AM AST Tue Dec 30 2025

An unstable weather pattern will persist on the first day of the
long term, as the main weather pattern is dominated by a mid- to
upper-level trough. This upper-to mid-level feature will create a
very unstable weather pattern, enhancing colder temperatures at
500 MB, ranging from -8 to 9 degrees. Meanwhile, at the surface,
moisture from a sinking frontal boundary over the Caribbean and
instability from the pre-frontal trough will align perfectly with
the upper instability, increasing the frequency and coverage of
showers during the day. Given the variability of winds due to
weakening of the pressure gradient resulting from the surface pre-
frontal trough, the coverage and movement of showers will be slow
and widespread across the mountain sections. Upper conditions
will rapidly improve as the subsidence side of the upper-level
trough moves eastward, and a more stable condition will dominate.
At 500 MB, a ridge will move in, warming temperatures from -9 to
-5 degrees. Stable conditions will persist from Saturday into
Monday; however, at the surface, shallow patches of moisture
dragged by the east-southeasterly wind flow will allow some
showers in the morning across the eastern side and across the
interior and western Puerto Rico for the afternoon. There are some
discrepancies in the amount of available moisture (relative
humidity %) on those days, with the ECMWF calling for a wetter,
more seasonal pattern.

On Tuesday again, weather conditions will deteriorate as another
upper-level trough moves into the Caribbean. Combined with the
instability, values of Relative humidity between 700 and 300 MB
show an increase in moisture, which will induce a more showery
pattern.

&&

.AVIATION...
(18Z TAFS)
Issued at 115 PM AST Tue Dec 30 2025

Mainly VFR conds expected across all terminals during the forecast
period. Passing showers will result in VCSH for TJSJ aft 30/23Z.
Winds from the ESE will become light and VRB after 30/23Z,
increasing from the SE btwn 8-12 kt, with higher gusts and sea
breeze variations aft 31/13-14Z.


&&

.MARINE...
Issued at 115 PM AST Tue Dec 30 2025

An east-to-southeast wind flow is expected to continue as a
frontal boundary approaches from the west, increasing the
potential for showers and thunderstorms. Pulses of long-period
northerly swell will persist across the Atlantic waters and
passages.

&&

.BEACH FORECAST...
Issued at 115 PM AST Tue Dec 30 2025

Pulses of northerly swell will continue to propagate across the
regional waters, resulting in a high to moderate risk of rip
currents along north-facing beaches of Puerto Rico, Culebra, St.
Thomas, and St. John during the next few days.

&&

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

     High Rip Current Risk until 6 PM AST this evening for PRZ010.

VI...High Rip Current Risk through late tonight for VIZ001.

AM...None.
&&

$$

SHORT TERM...OMS
LONG TERM....MIDNIGHT CREW
AVIATION...GRS

NWS SJU Office Area Forecast Discussion