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983
FXCA62 TJSJ 251844
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
244 PM AST Fri Sep 25 2026

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

.KEY MESSAGES...
Issued at 240 PM AST Fri Sep 25 2026

- Limited showers and isolated thunderstorms are expected this
afternoon across portions of the interior and northwestern Puerto
Rico, increasing in coverage each afternoon during the weekend,
which could result in a limited to elevated flood risk.

- A Heat Advisory remains in effect until 4 PM AST this afternoon
across Puerto Rico and the U.S. Virgin Islands. Heat will remain a
persistent risk throughout the weekend, with the possibility of
additional heat-related products being issued.

- A moderate risk of rip currents is expected to continue along
northwestern to eastern beaches of Puerto Rico and northern U.S.
Virgin Islands through at least Saturday night, then potentially
increasing to high on Sunday into early next week.


&&

.Short Term(This evening through Sunday)...
Issued at 240 PM AST Fri Sep 25 2026

Tranquil weather has prevailed across the islands. Heat indices have
reached the upper 90s to the mid-110s degrees Fahrenheit across
coastal areas, while values in the upper 80s to upper 90s have been
experienced across interior portions. Thus, the Heat Advisory was
extended until 4 PM.

An air mass with slightly below-normal precipitable water (PWAT)
values will move into the region, marginally limiting deep
convection. Nonetheless, an upper-level trough will continue to
promote enhanced instability, with below-normal 500-mb temperatures.
This scenario, combined with mostly clear skies allowing for
increased daytime heating, will promote localized shower and
thunderstorm activity during the afternoon. However, the onset of
convection may be delayed compared to previous days. An ESE flow
will steer this activity mainly toward northern to northwestern
Puerto Rico.

On Saturday, the below-normal moisture air mass will settle across
the CWA, with low concentrations of Saharan dust embedded within it.
This should favor a weather pattern similar to today. Although drier
air filtering into the mid-levels will be the main limiting factor,
available low-level moisture and enhanced instability associated
with the upper-level trough deepening in our vicinity should remain
sufficient to support localized afternoon convection. By Sunday, a
tropical wave will increase precipitable water (PWAT) values to near
seasonal levels, while the upper-level low remains in our vicinity.
This combination could promote a more active afternoon, particularly
across the western half of Puerto Rico.

Overall, excessive rainfall and elevated heat threat will remain the
main hazards through the short-term period. An elevated risk of
excessive rainfall will be localized across northwestern Puerto Rico
today and Saturday, while surrounding areas will remain under a
limited risk. On Sunday, conditions are expected to become more
favorable for shower and thunderstorm activity across interior and
northwestern portions of Puerto Rico, as well as in streamers
developing downwind of the smaller islands and El Yunque. As a
result, a limited excessive rainfall risk will extend across the
eastern half of Puerto Rico and Vieques for that day.

At most, the eastern half of the CWA can expect a limited excessive
rainfall risk, which may result in ponding of water on roadways and
in poorly drained areas. Some rivers across southeastern Puerto Rico
may respond quickly to heavier rainfall and produce localized
streamflow flooding. However, these impacts are expected to remain
mainly localized. Additionally, landslides and rockfalls are
possible in areas with saturated soils and steep terrain. Frequent
lightning and gusty winds can also be expected with the strongest
thunderstorms.


&&

.Long Term(Monday through next Thursday)...
Issued at 248 AM AST Fri Sep 25 2026

No major changes to the long term forecast. A tropical upper-
tropospheric trough (TUTT) will continue to linger in the vicinity
of the CWA. While it will shift from the northeast to southeast of
the islands by late week, the position will remain unfavorable for
the development of showers and thunderstorm over the forecast region
as it will favor upper-level convergence. The low is expected to
move away from the forecast area by late next week. Over the eastern
Atlantic Ocean a low-level high pressure system will promote an ENE
wind flow with a shift to ESE flow by the end of the week. The
conditions are expected to become breezy to locally windy across the
US Virgin Islands and Puerto Rico from Monday into late-week. The
potential shift in wind direction may aid in the development of
streamers from the US Virgin Islands, Culebra, Vieques, and El
Yunque rainforest. While a tropical wave is expected to reach the
forecast region between Monday and Tuesday the bulk of the moisture
field associated with the system will remain to the south of the US
Virgin Islands and Puerto Rico with lower than average precipitable
water (PWAT) values intruding the region. Nonetheless, on Monday the
atmospheric column is expected to be moister which may be favorable
for the development of convective activity. Dry conditions in the
low-to-upper levels is expected to persist into the week.

Conditions for the remainder of the forecast period are thus
expected to be driven by local effects, particularly favoring
afternoon showers and thunderstorms over the northwest and interior
of Puerto Rico and some passing morning showers over the US Virgin
Islands and eastern Puerto Rico. Mid-tropospheric temperatures are
also forecasted to be below-to-around average for the season,
increasing the potential for the development of deep convective
cells. Risks associated to extreme heat continue to be one of the
main concerns throughout the rest of the forecast period with 925 mb
temperatures expected to be 2 standard deviations above normal
ranges for the season into early next week showing a decreasing
trend into mid week. Citizens ands visitors are invited to stay
alert of the evolving weather conditions as we move into the weekend.

&&

.AVIATION...
(18Z TAFS)
Issued at 240 PM AST Fri Sep 25 2026

Mainly VFR conds are expected across all TAF sites through most of
the forecast period. However, VCTS & -TSRA are possible and could
result in intermittent/brief MVFR conds and mountain obscurations at
TJBQ thru 25/21z.  VCSH are expected across TJSJ and USVI sites
during the overnight. Mainly SE winds up to 10-12 kt and sea breeze
variations. Light and variable winds expected overnight.

&&

.MARINE...
Issued at 240 PM AST Fri Sep 25 2026

Light to moderate east to southeast winds will prevail tonight
through Saturday, generally at 10 to 15 knots or less, with seas
mostly between 2 and 4 feet. A weak northerly swell will continue to
spread across the Atlantic waters and passages, gradually increasing
seas through the weekend. Marine conditions are expected to
deteriorate from Sunday into early next week as the northerly swell
becomes more pronounced and easterly winds strengthen, with seas
building to around 5 to 6 feet and occasionally up to 8 feet across
portions of the offshore Atlantic waters by Monday. Small Craft
Advisory conditions may become possible across the Atlantic waters
and local passages early next week. Scattered showers will remain
possible tonight and Saturday, with isolated thunderstorms capable
of producing locally higher winds and seas, frequent lightning, and
brief reductions in visibility.

&&

.BEACH FORECAST...
Issued at 240 PM AST Fri Sep 25 2026

A moderate risk of rip currents will continue tonight along the
northern and northeastern beaches of Puerto Rico and Culebra, while
a low risk prevails elsewhere. On Saturday, the moderate risk will
expand into portions of northwestern and western Puerto Rico and the
northern U.S. Virgin Islands. Surf conditions could become
increasingly hazardous from late Sunday into early next week as
another weak northerly swell reaches the local Atlantic waters, with
breaking waves generally increasing to 5 to 6 feet along the
northern and western beaches of Puerto Rico. This swell may result
in a high risk of rip currents along the most exposed beaches during
this period.

Other beach hazards through the weekend will include heat during the
late morning and afternoon hours. Afternoon showers and isolated
thunderstorms will also remain possible each day, particularly along
the western beaches of Puerto Rico, where lightning, brief heavy
rainfall, and locally gusty winds may occur. If thunder is heard,
leave the beach and water immediately and seek safe shelter.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...JCP/CVB
AVIATION...YZR
LONG TERM...RVM/MRR
MARINE/BEACH...CVB

NWS SJU Office Area Forecast Discussion