781
FXCA62 TJSJ 151815
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
215 PM AST Sat Nov 15 2025

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

.KEY MESSAGES...
Issued at 215 PM AST Sat Nov 15 2025

* An unstable wet pattern is expected to persist across Puerto
  Rico and the US Virgin Islands throughout the weekend.

* There is a high chance of observing strong afternoon thunderstorms
  across Puerto Rico the rest of this afternoon and tomorrow.

* There is a moderate chance of observing heavy rain and isolated
  thunderstorms across the U.S. Virgin Islands this evening and
  tomorrow.

* The exposed north-facing beaches in Puerto Rico and the northern
  U.S. Virgin Islands will have a moderate risk of rip currents,
  especially by Sunday.

&&

.Short Term (This evening through Monday)...
Issued at 215 PM AST Sat Nov 15 2025

The TJSJ RAOB 12z sounding data indicated a weak southeasterly
wind flow at the surface, which prevailed during the morning
hours. They allowed much of this morning`s rain to remain almost
stationary across portions of the regional waters. The skies were
mostly sunny, but southerly winds pushed patches of clouds across
the U.S. Virgin Islands. Some clouds were also noted over the
southern plains of Puerto Rico. From mid-morning onward, cloudiness
began to increase over Puerto Rico, especially in the mountainous
areas, resulting in the development of showers. Additional slow
moving shower activity and thunderstorms are forecast to continue
through the afternoon hours. Maximum temperatures ranged from the
upper 80s across the coastal sections to the low 80s in the mountain
areas.

A prefrontal trough lingering north of the region will promote
low-level moisture to pool over the islands throughout the
weekend, till it dissipates. Additionally, a mid-to-upper-level
trough amplifying near the Northeast Caribbean will slowly
increase instability across the region the rest of today and
Sunday. Thus, the 500 mb temperatures indicated a cooling trend,
with values below normal, which could enhance the formation of
thunderstorms when combined with orographic effects, sea breeze,
and diurnal heating. Additionally, the weak steering wind flow
will allow the activity that develops to remain longer than usual,
increasing the potential for flooding. Therefore, we have a
moderate risk of flooding rains in the mountain areas of PR, with
a slight to moderate risk of spreading to the surrounding coastal
locations, from which they originate. Some showers will impact the
US Virgin Islands, but there is currently a non-to-slight risk of
flooding at this time.

Overnight, the proximity of the prefrontal trough interacting
with the amplifying trough, combined with above-average, warmer-
than- normal sea surface temperatures, will allow the formation of
showers and thunderstorms across the Atlantic Waters and
Caribbean Passages. There is a slight to moderate chance of
observing this activity slowly drift into the coastal locations,
especially along the northern coastline of PR. A mixture of
sunshine and clouds will prevail on Sunday morning, followed by
the formation of afternoon convection, once again over the
mountain areas. However, there is a better potential for the
activity to spread into the north and northwest coast of PR. The
US Virgin Islands will experience a few showers crossing the
islands, resulting in occasional periods of moderate to locally
heavy rainfall.

A seasonal weather pattern is expected to return on Monday, as the
upper-level flow becomes more zonal and the frontal boundary
finally dissipates, leaving high pressure across the Central
Atlantic to be the dominant surface feature. Thus, a mixture of
sunshine and clouds with occasional passing showers will be the
predominant weather pattern.

&&

.Long Term (Tuesday through Saturday)...
Issued at 425 AM AST Sat Nov 15 2025

During early Tuesday into early Wednesday, the islands will be
mainly influenced by a surface high pressure over the central
Atlantic, resulting in mostly east-southeasterly winds. Embedded
within this wind flow are patches of trapped tropical moisture
with precipitable water values between 1.4 and 1.6 inches.
Although this moisture will be present and concentrated near 850
MB, drier conditions are expected from 500 to 250 MB due to a
stable weather pattern. Global models suggest this setup will
bring some showers across the U.S. Virgin Islands and eastern
Puerto Rico at times, followed by afternoon convection over
western Puerto Rico. Since the available moisture is expected to
remain shallow, rainfall should be only locally heavy, with a low
probability of urban or small-stream flooding.

A more stable and drier weather pattern is forecast from late
Thursday into Friday. A broad and strengthening surface high
pressure system exiting the eastern coast of the United States and
extending into the central Atlantic will establish a
northeasterly wind flow across the region. This shift in the wind
pattern will transport a drier and cooler air mass over the
islands, limiting shower development and improving overall weather
conditions. This shift will also support a cold-advection pattern
mainly across the local northern waters. According to the 925 MB
temperature fields, temperatures are expected to decrease across
the islands.
&&

.AVIATION...
(18Z TAFS)
Issued at 215 PM AST Sat Nov 15 2025

Unstable weather pattern will prevail across the local flying area
tonight. Occasional periods of MVFR conds are possible due to VCTS
or TSRA across TJSJ, TJPS and TJBQ resulting in lower ceilings,
brief higher winds, and reduced vis. After 15/23Z, VFR conds will
prevail, but prds of VCSH/VCTS cannot be ruled out, especially near
JBQ/JSJ overnight. There is a moderate chance to observe an active
afternoon on Sunday. Expect S-SE winds btwn 5-10 kt with higher
gusts and sea breezes, becoming calm to light and VRB overnight.

&&

.MARINE...
Issued at 215 PM AST Sat Nov 15 2025

A pre-frontal trough to the north will continue to promote a light
south to southeasterly wind flow through Monday. Strong showers
and isolated thunderstorms could lead to locally hazardous
conditions for small craft, particularly during the weekend. A
surface high-pressure system will build across the central
Atlantic by Monday, bringing moderate easterly winds by Monday or
Tuesday. Additionally, a north to northeasterly swell will spread
across the local waters starting Sunday, with a second pulse
expected by Tuesday.

&&

.BEACH FORECAST...
Issued at 215 PM AST Sat Nov 15 2025

Beachgoers can expect coastal conditions to continue improving
today, with a low risk along the west and southern coasts of PR
and the USVI. However, another north-northeasterly swell will
increase the risk of rip currents to moderate on Sunday, turning
high on Monday. A second pulse will maintain the risk high on
Tuesday.

Afternoon thunderstorms will promote lightning activity. We
encourage our locals and visitors to remain vigilant in case they
hear thunder, as lightning can strike remote locations from where
it forms.

&&

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

$$

SHORT TERM/AVIATION...CAM
LONG TERM...LIS
PUBLIC...YZR