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740
FXCA62 TJSJ 231858
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
258 PM AST Tue Dec 23 2025

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

.KEY MESSAGES...
Issued at 246 PM AST Tue Dec 23 2025

* Marine and coastal conditions will deteriorate late tonight
  through the weekend as increasing northeasterly winds and multiple
  pulses of long-period northerly swell create choppy to rough seas
  and hazardous conditions for small craft.

* Rip current risk will increase to high along exposed northern and
  eastern beaches of Puerto Rico, Culebra, and the USVI as northerly
  swell builds and persists through the end of the week. A High Surf
  Advisory cannot be ruled out.

* A frontal boundary will pass tonight through early Thursday,
  increasing the frequency of showers, mainly overnight and during
  the morning hours. Rainfall amounts are expected to remain
  limited, with minor ponding of water on roads and in poorly
  drained areas possible.

* Persistent northeasterly flow will keep temperatures seasonably
  cool to slightly below normal, particularly at night and across
  higher elevations. Patchy fog may develop late in the week during
  the late night and early morning hours, especially across interior
  and valley locations of Puerto Rico, leading to brief reductions
  in visibility.

&&

.Short Term(This evening through Thursday)...
Issued at 246 PM AST Tue Dec 23 2025

Passing showers persisted during the morning hours, mainly moving
over the northern and eastern portions of Puerto Rico, including
Culebra, as well as St. Thomas and St. John in the U.S. Virgin
Islands. Based on WSR-88D rainfall estimates, some areas ranged
between 1.0 and 1.5 inches. Minimum temperatures over urban and
coastal areas remain in the low to mid 70s, with localized areas in
the high 60s; On the other hand, higher elevations remained in the
low to mid 60s. Breezy conditions also persisted, under a
northeasterly wind flow, as stations reported wind gusts between 25
and 28 mph in the higher elevations and up to 34 mph detected by the
San Juan buoy. These conditions are likely to continue throughout
the day.

No major changes were introduced to the short-term forecast,
although tonight is forecast as the wettest day of the period.
Satellite-derived products highlight an area of high moisture
content associated to a frontal boundary north of the region,
with PWAT values between 1.5 and 1.6 inches, near the above
climatological normal. From the probabilistic guidance of the GFS
and ECMWF, theres high confidence in increasing moisture content
in the low and mid levels for this time of the year, with relative
humidity between 70 and 80% in the low levels and 40 - 50% in the
mid levels. Under a northeasterly wind flow, the frequency of
showers should increase late tonight, moving over windward
sections of the islands, some reaching interior portions of Puerto
Rico. Although significant flooding is not expected, rainfall
accumulations could lead to ponding of water over roadways, urban,
and poorly drained areas, with a low chance of flooding.

Based on the latest model guidance, moisture content will gradually
decrease as a surface high pressure builds over the western
Atlantic, weakening the frontal boundary. Nevertheless, a deep-
layered trough will introduce instability to the forecast, with
cooler than normal 500 mb temperatures (between - 9 and -10
degrees Celsius), favoring deep convection. Additionally, strong
winds (250 mb winds between 70 and 80 kt) in the upper levels may
allow ventilation and cloud growth. Hence, afternoon convection is
expected across southwestern portions of Puerto Rico, then an
advective cooling pattern with showers and isolated thunderstorms
developing over the regional waters and moving over windward
sections of the islands on Tuesday night (Christmas Eve) into
early morning Wednesday (Christmas Day). Although widespread
thunderstorms are not expected, isolated thunderstorms may produce
localized flooding, gusty winds, and lightning. Hence, the
flooding and lightning risk will remain limited. By Thursday
afternoon, a drier air mass should filter into the region,
limiting shower activity for the rest of the period. Under a
northeasterly wind flow, cooler temperatures are expected across
the islands, with minimum temperatures lower in elevations in the
high 60s and mid 70s, and higher elevations in the mid 50s to low
60s.

&&

.Long Term(Friday through next Monday)...
Issued at 537 AM AST Tue Dec 23 2025

Drier air behind the frontal boundary will dominate throughout the
the period. Precipitable Water (PWAT) values are forecast at
around to below an inch with isolated patches of moisture (PWAT up
to around 1.2 in) reaching the area and promote passing showers
from time to time. Although low PWAT values are forecast, upper
troughs will move northeast of the area during the latter part of
this week. building surface high over the western Atlantic and a
frontal low over the north-central Atlantic will promote
northeasterly steering flow to start the period. Model guidance
suggests that winds will gradually veer to start the next week,
promoting southeasterly flow by the end of the period. Under the
northeasterly flow, 925 mb temperatures are forecast to be below
normal. Minimum temperatures are forecast in the 50s to low 60s
across higher elevations of PR, in the upper 60s to mid 70s across
lower elevations of PR, and in the low to mid 70s across the
USVI. Maximum temperatures are forecast around the mid 80s across
lower elevations of the islands, with isolated/urban areas a bit
higher. This will likely enhance patchy fog across sectors of
interior Puerto Rico.

&&

.AVIATION...
(18Z TAFS)
Issued at 246 PM AST Tue Dec 23 2025

Most VFR conds expcd this aftn across all TAF sites. NE winds
will reduce btwn 6 - 10 kt, becoming VRB at JPS. Tonight,
-SHRA/+SHRA expcd over the northern terminals (JSJ, JBQ, JIX)
particularly 24/03-06z, which may reduce CIGs/VIS, leading to MVFR
conds through at least 24/12z. Although conds aren`t favorable,
TSRA cannot be ruled out across these terminals. Winds will
increase by 24/12-13z, around 15 kt with gusts up to 25 kt. VCTS
is pssbl at JPS by 24/16-18z due aftn convection.

&&

.MARINE...
Issued at 246 PM AST Tue Dec 23 2025

Buoy 41043 is already indicating long-period NNE swell with periods
near 14 seconds, confirming the arrival of a long-period northerly
swell associated with the frontal low. This swell will spread across
the offshore Atlantic waters late tonight, resulting in choppy to
rough seas and hazardous conditions for small craft. Seas are
expected to build to 6 to 9 feet, spreading into the nearshore
Atlantic waters and local passages. Small Craft Advisories remain in
effect; for additional information, refer to the Marine Weather
Message (MWWSJU). Another pulse of northerly swell late in the
workweek will support deteriorated marine conditions through the
weekend.

&&

.BEACH FORECAST...
Issued at 246 PM AST Tue Dec 23 2025

The forecast remains on track, with conditions deteriorating this
evening as a northerly long-period swell arrives. Buoy 41043 is
already indicating long-period NNE swell with periods near 14
seconds. This swell will increase the risk of rip currents to high
for exposed northern beaches by this evening and continue through
the rest of the week. A High Surf Advisory may be required with this
swell event, which could result in localized beach erosion and
dangerous swimming conditions. Another pulse of northerly swell will
arrive later in the workweek, supporting hazardous beach conditions
through the weekend. For further information, refer to the Coastal
Hazard Message (CFWSJU).

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from 6 PM AST this evening through late
     Thursday night for PRZ001-002-005-008.

VI...None.
AM...Small Craft Advisory until midnight AST Thursday night for
     AMZ711.

     Small Craft Advisory from noon Wednesday to midnight AST
     Thursday night for AMZ712-716-723-741-742.

&&

$$

SHORT TERM/AVIATION...MNG
LONG TERM...MRR
MARINE/BEACH FORECAST...CVB

NWS SJU Office Area Forecast Discussion