996
FXCA62 TJSJ 300805
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
405 AM AST Tue Dec 30 2025

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

.KEY MESSAGES...
Issued at 401 AM AST Tue Dec 30 2025

* Hazardous coastal conditions will persist across the northern
  coastal areas of Puerto Rico, Culebra, and St. Thomas, where a
  high risk of rip currents remains in effect.

* Easterly wind flow will return today; therefore, more
  seasonable temperatures are expected today and tonight.

* Puerto Rico and the U.S. Virgin Islands:
For tomorrow, the last day of 2025, a more unsettled weather
pattern is forecast with the arrival of moisture from a frontal
boundary and added instability from an upper-level trough.

&&

.Short Term(Today through Thursday)...
Issued at 401 AM AST Tue Dec 30 2025

Skies will remain mostly clear to partly cloudy today across much
of the forecast area, as the overall pattern remains similar to
the past several days. Ridging aloft with dry mid-levels will
continue to promote relatively stable weather conditions. At the
surface, high pressure over the central Atlantic will continue to
shift eastward, resulting in winds veering from east-northeast to
a more southeasterly component, remaining mostly light to
moderate. These southeasterly winds will persist across the region
through the short- term forecast period. Only isolated brief
showers are expected, mainly over windward coastal areas during
the morning hours and across the western interior of Puerto Rico
during the afternoon due to local effects, as well as over the
surrounding waters at times. Temperatures will remain slightly
below normal, resulting in pleasant conditions across the islands
once again.

From Wednesday into Thursday, weather conditions will become more
variable as a deepening polar trough moves over the region,
enhancing dynamics aloft. Model guidance continues to indicate
falling mid-level heights and 500 mb temperatures dropping to around
-9 to -10 C. This will result in steeper low- to mid-level lapse
rates and a more favorable environment for convective development.
At lower levels, a surge of tropical moisture is expected to arrive,
with precipitable water values increasing to near 1.8 to 2.0 inches
and 700-500 mb relative humidity values rising well above 2 standard
deviations above climatological normals. Despite the increasingly
favorable dynamic setup, guidance remains consistent in keeping the
highest moisture content and more organized convective activity
focused west of the local islands, particularly over Hispaniola and
the Mona Passage. As a result, shower and thunderstorm coverage over
Puerto Rico and the U.S. Virgin Islands may not be as widespread,
with much of the activity favoring the waters west and northwest of
Puerto Rico.

Still, periods of shower activity are expected across the area.
Afternoon convection will be possible over the western and interior
sections of Puerto Rico, particularly on Thursday, driven by the
combination of favorable dynamics aloft, diurnal heating, and local
effects. Additionally, nighttime and early morning trade wind
showers, along with isolated thunderstorms developing over the
regional waters, could affect coastal areas, particularly along the
western half of the CWA. Brief heavy rainfall, gusty winds, and
isolated lightning strikes will be possible with stronger
thunderstorms, although widespread activity is not anticipated.

Overall, the short-term period will feature a transition from
todays relatively stable and pleasant conditions toward a more
unsettled pattern by mid to late week, with increasing moisture and
enhanced instability aloft, while the highest impacts are expected
to remain mainly over the surrounding waters.

&&

.Long Term(Friday through 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...
(06Z TAFS)
Issued at 401 AM AST Tue Dec 30 2025

Mainly VFR conds exp across all TAF sites thru the fcst pd. Brief
- SHRA/VCSH psbl at times, mainly at TJSJ/TIST/TISX, with SCT-BKN
cigs btw FL030FL060 at times. Any VIS/CIG reductions expected to
be brief. Winds lgt/vrb ovrngt, bcmg ESESE at 812 kt aft 14Z,
then diminishing again aft 23Z.

&&

.MARINE...
Issued at 401 AM AST Tue Dec 30 2025

A surface high pressure system moving eastward from the western
into the central Atlantic, interacting with the remnants of an old
frontal boundary, will maintain a light easterly wind flow across
the region through Tuesday. From late Wednesday into Friday, an
approaching frontal boundary combined with a strengthening high-
pressure system over the central Atlantic will result in a
moderate east-to-east-southeast wind flow, increasing the
potential for showers and isolated thunderstorms and enhancing
localized hazardous marine conditions. During the period, pulses
of long-period northerly swell will continue to propagate across
the Atlantic waters and Caribbean passages through the middle of
the week. Small craft operators are urged to exercise caution,
particularly across the exposed Atlantic waters and Caribbean
passages.


&&

.BEACH FORECAST...
Issued at 401 AM AST Tue Dec 30 2025

A long-period northerly swell will continue to propagate across
the northern regional waters, resulting in a persistent high risk
of dangerous rip currents along north-facing beaches of Puerto
Rico, Culebra, St. Thomas, and St. John. Therefore, a Rip Current
Statement will remain in effect through at least Tuesday
afternoon. Recent data from buoy 41043, located about 170 nautical
miles north of San Juan, indicate another pulse of northerly
swell arriving across the islands, with wave heights up to 6 feet
and periods near 13 seconds. This swell energy will maintain
breaking waves along the northern coastal areas between 6 and 8
feet, with occasionally higher sets.

Given the forecast conditions, a high rip current risk is expected
to persist through Thursday, with gradual improvement as the
weakening swell dissipates. Nevertheless, even as conditions
improve, hazardous rip currents may still develop near groins,
jetties, reefs, and piers during periods of lower risk. Beachgoers
are advised to exercise caution at all times when entering the
water.

&&

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

     High Rip Current Risk through this afternoon for PRZ010.

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

AM...None.
&&

$$

SHORT TERM & AVIATION...CVB
LONG TERM, MARINE & BEACH FORECAST....LIS

NWS SJU Office Area Forecast Discussion