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127
FXCA62 TJSJ 050728 CCA
AFDSJU

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
328 AM AST Mon Jan 5 2026

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

.KEY MESSAGES...
Issued at 256 AM AST Mon Jan 5 2026

* An upper-level trough and frontal boundary will increase shower
  and thunderstorm activity today.

* There is an elevated flood risk through Tuesday across Puerto
  Rico, particularly during the afternoon and evening hours.

* Across the U.S. Virgin Islands, there is a limited flood risk
  through Tuesday, followed by a drying trend for the remainder of
  the week. A moderate risk of rip currents will prevail from
  midweek onward.

* Life-threatening rip currents are expected on Wednesday and
  Thursday along the northwest to northeast beaches of Puerto
  Rico.

&&

.Short Term(Today through Wednesday)...
Issued at 256 AM AST Mon Jan 5 2026

Similar to last night, mostly fair conditions prevailed across the
CWA, with most of the shower activity remaining across local waters
and some moving over portions of eastern Puerto Rico, including
Vieques. Since winds weakened and became light and variable, showers
persisted longer. CWOP and RAW stations reported mid-to-upper 70s
across coastal and lower elevations, and low to mid-60s across
higher elevations. Temperatures should slightly drop near sunrise,
with localized areas dropping into the upper 50s.

The short-term remains on track, with few changes for the end of the
period. Current satellite-derived products show the deep-layered
trough inducing a surface trough north of Hispaniola, producing
scattered showers and thunderstorms. As the trough approaches the
local area, a resulting cold region should move across the region,
weakening surface winds and becoming light and variable. As the col
moves out of the local area, AGL winds will strengthen and veer from
the northeast. Confidence is increasing between model solutions, as
ensembles are tending towards wetter conditions due to low to mid-
level moisture above climatological normal (between 70 and 80 %) and
high chance of PWAT values above 1.6 inches, not typical for this
time of the year. The latest guidance continues to suggest favorable
dynamics for deep convection, as cooler-than-normal mid-level
temperatures (between -10 and -11 degrees Celsius), and strong upper-
level winds (around 80kt), could lead to forced ascent, cloud
growth, and ventilation. The advective pattern will be the main
driver of showers and isolated thunderstorms throughout the day,
with the highest chance of flooding tonight into early Tuesday,
moving across local waters and windward sections of the islands.
Afternoon convection over the mountain ranges and southern hills of
Puerto Rico is still very likely, if cloud cover allows it. Due to
weakening winds, showers and thunderstorms will very likely become
stationary, producing higher rainfall accumulations and increased
flood potential. Over the U.S. Virgin Islands, mostly ponding of
water over roads, urban, and poorly drained areas, while southern
and eastern Puerto Rico will experience higher accumulations leading
to urban and small stream flooding, with a low chance of flash
flooding. Given the expected conditions, the flood threat will
remain limited to elevated. The lightning risk will remain limited,
though scattered thunderstorms across the local Atlantic waters and
passages cannot be ruled out.

The drier airmass seems to be delayed, expected to filter by late
Tuesday night instead of the afternoon, based on the latest
deterministic guidance of the GFS and AIGFS. Additionally, the 00z
solutions show enhanced upper-level divergence across the CWA,
meaning the presence of "troughiness" and instability aloft. With
the lingering moisture, the chance remains medium to high for the
development of showers and thunderstorms on Tuesday afternoon,
particularly over portions of interior and southwestern Puerto Rico.
Due to the expected rainfall accumulations and previous shower
activity, the flood potential will increase over the aforementioned
areas, hence, the flood threat will remain limited to elevated.  As
the trough migrates eastward, the subsidence side of the trough
should bring more stable conditions across the CWA on Wednesday.
With drier-than-normal conditions (PWATs between 1.0 and 1.2
inches), the probability of precipitation will remain low, bringing
mostly fair conditions across the islands. As winds remain from the
NE through most of the period, temperatures should remain
seasonal.

&&

.Long Term(Thursday through Monday)...
Issued at 256 AM AST Mon Jan 5 2026

A building surface high pressure over the western Atlantic will
promote moderate to locally fresh east to northeasterly trades
during the long term period. A weak induced surface trough northeast
of the region will bring a brief surge in moisture content late in
the workweek, while a drying trend is expected during the weekend.
At upper levels, a ridge from the southwestern Atlantic and a
developing TUTT-low from the central Atlantic will promote drier
air aloft and more stable conditions in general. Therefore,
showers that form through the period are not expected to produce
heavy rainfall or grow into thunderstorms. These showers will be
mainly driven by the increasing trades, favoring an advective
pattern at night, with showers moving briefly at times across the
USVI and along the east and north sections of PR. Shallow
afternoon convection is expected over the Cordillera and southern
sections of PR, but the flood risk will remain low as rainfall
accumulations are not expected to exceed an inch of rain per day.
A TUTT induced surface trough is expected to increase moisture
content from the northeast once again early next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 256 AM AST Mon Jan 5 2026

VFR conds should prevail most of the time across all TAF sites,
though a sfc trof approaching the CWA will bring -TSRA/+TSRA that
will lead to VCTS for most terminals aft 05/13z. PROB30s for JPS,
IST, and ISX btwn 05/18-21z, and for JSJ btwn 06/03-06z due -TSRA
reducing CIGs/VIS and resulting in brf MVFR conds. Winds from the NE
will slgtly increase, btwn 6 - 10 kt, around 05/13-14z, becoming
light and VRB once again after 05/23z.

&&

.MARINE...
Issued at 256 AM AST Mon Jan 5 2026

A frontal boundary with an associated polar trough approaching
the local waters will promote light northerly to northeasterly
winds, and an increase in shower and thunderstorm activity
through at least Tuesday. A long period northerly swell is
expected to arrive by midweek, building seas up to 6 feet and
occasionally higher, particularly across the Atlantic waters and
the Caribbean Passages. Small craft operators should continue to
monitor forecasts for potential changes in marine conditions.

&&

.BEACH FORECAST...
Issued at 256 AM AST Mon Jan 5 2026

A long period northerly swell will cause rough surf and life-
threatening rip currents by midweek across the north-facing beaches
of Puerto Rico. Breaking waves could range between 6 and 8 feet,
and occasionally higher, particularly on Wednesday. Elsewhere, the
risk will be moderate, except along the southern beaches where
the risk will remain low throughout the week.

&&

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

$$

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

NWS SJU Office Area Forecast Discussion