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447
FXCA62 TJSJ 231753
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
153 PM AST Wed Sep 23 2026

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

.KEY MESSAGES...
Issued at 146 PM AST Wed Sep 23 2026

 - Showers and isolated thunderstorms will remain possible this afternoon,
   particularly across interior and western Puerto Rico. Heavy
   rainfall may lead to ponding of water on roads, urban and small
   stream flooding, and isolated landslides in areas with
   saturated soils.

 - Shower and thunderstorm activity will increase tonight into Thursday
   as a surface disturbance moves across the region. Another
   increase in activity is possible Thursday into Friday as a weak
   tropical wave moves through. However, activity should be more
   localized. Periods of heavy rainfall could result in urban and
   small stream flooding, particularly in areas that receive
   repeated rainfall.

 - Heat-related risks will continue during the next several days, with
   Friday expected to be of greatest concern. Stay hydrated and
   limit prolonged exposure to the sun, particularly during the
   hottest part of the day.

 - The risk of rip currents will increase to moderate along many north-
   and east-facing beaches beginning Thursday. Additional weak
   swells are expected this weekend and could further increase the
   rip current risk, potentially reaching high levels at some
   beaches. Those planning beach activities this weekend should
   monitor the latest forecasts and beach conditions.

&&

.Short Term(This evening through Friday)...
Issued at 146 PM AST Wed Sep 23 2026

A tranquil weather pattern prevailed across the islands this
morning, with mostly clear skies observed in satellite imagery and
a few clouds over eastern Puerto Rico and the U.S. Virgin
Islands. Maximum temperatures across the local islands fluctuated
between the upper 80s and lower 90s, particularly across coastal
areas. Across the mountains, maximum temperatures ranged from the
lower to mid 80s. At around 11 AM AST, some cloudiness started to
develop in the vicinity of El Yunque and across the mountainous
sections of Puerto Rico. Winds were from the east-southeast at 15
mph or less, with gusty winds near coastal areas. At 12 PM AST,
some showers in streamer-like patterns moved from St. Croix into
the surrounding waters.

For the rest of tonight into Thursday, an induced surface trough
associated with a tropospheric upper-level trough will approach
the region, resulting in increasing moisture and cloudiness and
promoting an increase in shower and thunderstorm activity across
the local waters. At the same time, east-southeast winds will
persist due to the interaction between a broad surface high
pressure over the central Atlantic and lower pressure well to the
west. Under this wind flow, showers will continue to move across
the U.S. Virgin Islands and the windward sections of Puerto Rico
during the overnight and morning hours. Therefore, Thursday will
remain variable and unsettled, with periods of increased
cloudiness and showers expected throughout the day due to the
moisture field associated with the surface perturbation. Overall,
the pattern calls for an unsettled day, with a limited to elevated
flooding threat forecast, particularly across eastern Puerto Rico
tonight into Thursday morning, shifting to western and
northwestern Puerto Rico during the afternoon.

By Friday, atmospheric conditions will remain slighty favorable
for additional shower and thunderstorm development. A deep TUTT
and an associated cut-off low will position the region within a
more favorable upper-level divergent pattern, particularly across
the eastern of the forecast area, just over the Lesser Antilles.
At lower levels, precipitable water values will generally range
between 1.5 and 1.9 inches, remaining near to above climatological
normals at times. In addition, 500 mb temperatures around -7
degrees Celsius will provide sufficient instability for deeper
convection. Therefore, passing showers will remain possible across
windward areas during the morning, followed by locally and
diurnally induced convection during the afternoon, with
thunderstorms favoring western and northwestern Puerto Rico.

&&

.Long Term(Saturday through next Tuesday)...
Issued at 146 PM AST Wed Sep 23 2026

A couple of multi-level lows continue to be the main synoptic
features over the region. An upper-level low will shift to the
southwest of Puerto Rico and coupled with local effects will
continue to drive instability that favors the development of showers
and thunderstorms across the CWA. With the exception of Saturday,
when model guidance suggests that a drier air mass from low to upper
levels (700-250 hPa) accompanied with low levels of Saharan Dust
will lead to amenable weather conditions. Precipitable water (PWAT)
values are expected to be variable with lower values expected
Saturday into Sunday, becoming seasonal on Monday and returning to a
drier pattern Tuesday into Wednesday. A key feature for the weekend
will be drier low-to-upper levels (700-250 mb). Thus, any activity
that develops will heavily rely on the instability provided by the
low as well as mechanical lifting mechanisms driven by local
effects. A more humid vertical profile is expected on Monday making
the day more favorable for convective activity. The mid-tropospheric
temperatures will be well below the normal ranges for the season,
thus this may favor the development of deep convective cells into
early next week. Breezy conditions are expected to prevail on
Tuesday into Wednesday, along with the ESE windflow set by the low-
level low pressure system in the central to western Atlantic and a
surface high over the central Atlantic surrounding the remnants of
Fay. This ESE flow may favor the development of streamers off the US
Virgin Islands, Vieques, Culebra, and El Yunque rainforest and
convective activity from interior to west and northwest PR. One of
the main risks for the long-term period remains associated to the
extreme heat. Low-level (925 mb) temperatures are expected to be 2
standard deviations above normal levels, this accompanied with humid
low-levels and calmer wind conditions will lead to an elevated
extreme heat risk into early next week. Thus, we recommend
individuals limit outdoor activities and remain well hydrated.

&&

.AVIATION...
(18Z TAFS)
Issued at 146 PM AST Wed Sep 23 2026

VFR Conditions, with brief periods of MVFR, will persist at least
through 23/22Z. SHRA and TSRA are expected to develop across the
mountainous sections of Puerto Rico this afternoon, resulting in
brief reductions in VIS and lower ceilings in and around the
strongest activity. An approaching tropical wave and an induced
surface trough will promote increasing moisture and instability,
leading to an increase in SHRA/TSRA later in the forecast period.
Winds will persist from the E-SE at around 15 knots or less, with
sea breeze variations and gusty winds in and around TSRA.


&&

.MARINE...
Issued at 146 PM AST Wed Sep 23 2026

A surface perturbation moving from the east will cross the regional
waters tonight, increasing the frequency of showers, with isolated
thunderstorms possible. A weak tropical wave will then move across
the area Thursday night into Friday, maintaining periods of
increased shower and thunderstorm activity over the waters. A series
of weak northerly swells will reach the Atlantic waters and local
passages by the end of the workweek and continue into the weekend,
gradually building seas. However, seas are expected to remain below
Small Craft Advisory criteria. Winds will generally remain light to
moderate from the east to southeast through the period. Winds and
seas may be locally higher in and near thunderstorms.

&&

.BEACH FORECAST...
Issued at 146 PM AST Wed Sep 23 2026

A moderate risk of rip currents is expected along the north- and
east-facing beaches of Puerto Rico and the U.S. Virgin Islands
tomorrow through the next few days. A series of weak northerly
swells is expected to reach the local waters and passages by the end
of the workweek and continue into the weekend. Although these swells
are expected to remain relatively weak, they could result in an
increased rip current risk, potentially reaching high levels at some
northern exposed beaches by this weekend.

Beachgoers should continue to monitor the latest forecasts and beach
conditions, particularly if planning activities along north-facing
beaches this weekend. At a moderate or high risk, stronger or more
frequent rip currents can occur, particularly at beaches exposed to
the incoming swell. Additionally, periods of increased shower and
thunderstorm activity are expected through the end of the workweek.
Thunderstorms may produce frequent lightning, gusty winds, and
rapidly changing weather and marine conditions. If thunder is heard,
leave the beach and water immediately and seek safe shelter.
&&

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

$$

SHORT TERM & AVIATION...LIS
LONG TERM....MRR/RVM
MARINE, BEACH FORECAST & KEY MESSAGES...CVB

NWS SJU Office Area Forecast Discussion