Special Weather Statement, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
126 PM AST Mon Sep 22 2025

.KEY MESSAGES...

* A calm night will persist across the USVI, with limited
  cloudiness and shower activity.

* Tomorrow, another warm day is forecast, with heat indices
  reaching up to 111 degrees in coastal and urban areas.

* A tropical wave, with a medium chance of development over the next
  seven days, will bring an unsettled weather pattern to the
  islands from Wednesday through Friday.

* A moderate risk of rip currents is expected along the northern
  and eastern coastal areas.

&&

.SHORT TERM...Rest of today through Wednesday...

Mostly sunny to partly cloudy skies prevailed across Puerto Rico
and the U.S. Virgin Islands during the morning hours. Isolated
thunderstorms were developing around noon from streamers downwind
of the USVI and from el Yunque area into San Juan and vicinity.
Another hot day prevailed across all the islands as high temperatures
ranged from the low to mid-90s across most coastal counties, with
heat indices between 108F-115F. Winds were from the east between
10 and 15 mph with sea breeze variations and higher gusts at times.

For the rest of today, locally induced thunderstorms are expected
to develop along portions of the Cordillera and western PR. Urban
and small stream flooding can be expected as well as strong gusty
winds. Meanwhile, a drier air mass with suspended Saharan dust
will continue to filter across the region, briefly, but enough to
cause hazy conditions through at least tonight. Another hot day is
expected on Tuesday, but heat indices might not reach extreme heat
warning criteria as winds will turn more east to northeast due to
an approaching tropical wave. This wind shift will also cause
convective development mainly over central and west/southwest PR.

By late Tuesday and Wednesday, a strong tropical wave, located
near 55W, will bring an increase in shower and thunderstorm
activity across the region. This tropical wave currently has a low
chance of development into a tropical system during the next 2
days, however, squally weather and periods of heavy rainfall will
increase with the wave passage from late Tuesday into Wednesday.
The flooding threat will increase in general across all the
islands through midweek. Please refer to hydro section for more
information.

.LONG TERM...Thursday through Monday...

/From previous discussion issued at 521 AM AST Mon Sep 22 2025/

On Thursday, the tropical wave being monitored by the National
Hurricane Center will continue to move across the region, increasing
the frequency of showers and thunderstorm activity across Puerto
Rico and the U.S. Virgin Islands. The system is located over the
central tropical Atlantic with a low probability of development,
with near 10 percent within 48 hours and around 60 degrees over the
next 7 days. Additionally, a weak upper-level trough, combined with
southeasterly flow around the Atlantic ridge, will sustain a steady
influx of tropical moisture through early Friday. This pattern
supports a prolonged period of unsettled weather with daily rounds
of heavy rainfall and thunderstorms. Model guidance keep suggesting
precipitable water values between 2.0 and 2.3 inches or above normal
values for this time of the year, along with mid-level temperatures
of -6 to -8 degrees Celsius, enhancing the risk for deep convection
and potentially having limited to elevated risk of flooding through
Friday.

Given the expected wet pattern on previous days and the
already saturated soils, the main threats include flash flooding,
rapid river rises, and landslides in vulnerable terrain. Tropical
development appears more likely by mid to latter part of this week
as the system moves west-northwestward to northwestward across the
central Atlantic. Nevertheless, the weather feature will be
monitored closely with updates from official sources such as the
National Hurricane Center.

Later in the weekend a slight and gradual improvement in weather
conditions is expected as a drier air mass filters into the region,
bringing a temporary break in the unsettled pattern.

By the beginning of the workweek, model guidance indicates that
another tropical wave may approach the region. While it is too early
to determine development potential, this system will need to be
monitored closely as it draws nearer.

Temperatures are expected to gradually increase Friday into
Saturday. Given the available moisture and the fact that models
continues to show that winds will also become lighter an Extreme
Heat Warning could potentially be issued. However, this will largely
depend on how the tropical wave evolves and if indeed the
significant cloudiness moves out of the area by the end of the
workweek.

&&

.AVIATION...

(18Z TAFS)

SHRA/TSRA in and around TJSJ/TJBQ may cause tempo MVFR conds thru
22/21z. Across the rest of the PR/USVI terminals, mostly VCTS
expected. Meanwhile, HZ due to Saharan dust will continue to
filter over the local area through at least tonight. VFR conds
expected overnight thru 23/16z. The 22/12z TJSJ sounding indicated
east winds up to 12 kt blo FL100.

&&

.HYDROLOGY...

As a robust tropical wave approaches the islands, conditions will
become increasingly favorable for flooding across Puerto Rico and
the Virgin Islands. The heaviest rainfall is anticipated late on
Wednesday into early Thursday.

Some of the factors that will work in favor of the rainfall event
are that moisture content is expected to be above normal, and the
wave is expected to be well defined from the surface to the mid-
levels too. This will result in a period of increased showers, with
the heaviest activity focusing over the vicinity of the Virgin
Islands and the northern and eastern portions of Puerto Rico. So
far, rainfall accumulations are expected to range from 2 to 4
inches, with isolated amounts up to 6 inches for the period of
Tuesday-Thursday.

Previous rains across the islands have led to saturated soils along
the northern and western half of Puerto Rico, St. Thomas and western
St. Croix, according to the latest National Soil Moisture Analysis
from the National Water Model. Also, data from the Puerto Rico
Agricultural Water Management Program further suggest saturation
along most of western Puerto Rico and St. Croix. Most of the rivers
monitored by the US Geological Survey indicate that streams are
running near normal, with the exception of a couple of rivers in the
east-southeast that are running just below the 25% percentile. Areas
that are saturated or where river flows are above normal will react
quicker, as most of the rainfall will turn into excessive runoffs
and flows.

Hazards and impacts associated with this event are expected to be
urban and small stream flood, while isolated flash flooding cannot
be ruled out. Landslides in areas of steep terrain, water surges,
rapid river rises, and some streams reaching flood stage are also
expected.

Users that live or work near flood prone areas should monitor the
weather in the upcoming days, and stay tuned to any flood product
issued by this Weather Forecast Office.

&&

.MARINE...

Major Hurricane Gabrielle is located well to the north over the
western Atlantic. An induced surface trough will maintain moderate
easterly winds across the region through tonight and into tomorrow.
Over the next few days, seas will range between 3 and 5 feet.
On Wednesday, a vigorous tropical wave will move into the islands,
increasing the potential for thunderstorms and leading to localized
hazardous marine conditions. These storms may produce frequent
lightning over exposed waters. In addition, an increase in surface
winds is forecast from Wednesday onward, particularly across the
offshore Atlantic waters, where small craft operators should
exercise caution.

&&

.BEACH FORECAST...

A moderate risk of rip currents will persist through the week along
the northern and eastern beaches of Puerto Rico and St. Croix.
Breaking waves should remain up to 5 feet along these areas through
the remainder of the period. Lightning strikes will be a hazard to
most coastal areas of the islands on Wednesday and Thursday due to
the passage of a tropical wave.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning until 4 PM AST this afternoon for
     PRZ001>005-007-008-010-011.

     Heat Advisory until 4 PM AST this afternoon for PRZ012-013.

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

AM...None.
&&

SHORT TERM/AVIATION...DSR
KEY/BEACH/MARINE...LIS
HYDRO...ERG
LONG TERM....MMC

Hazardous Weather Outlook
National Weather Service San Juan PR
503 AM AST Mon Sep 22 2025

AMZ711>745-PRZ001>013-230915-
San Juan and Vicinity-Northeast-Southeast-Eastern Interior-
North Central-Central Interior-Ponce and Vicinity-Northwest-
Western Interior-Mayaguez and Vicinity-Southwest-Culebra-Vieques-
The nearshore and off shore Atlantic and Caribbean Coastal Waters-
503 AM AST Mon Sep 22 2025

This Hazardous Weather Outlook is for portions of Puerto Rico.

.DAY ONE...Today and Tonight

.Lightning...Isolated thunderstorms, particularly across
interior/western Puerto Rico in the afternoon. Stay alert and be
prepared to take shelter if storms develop.

.Excessive Rainfall...Flooding in urban areas, roads, small
streams, and washes, particularly across interior/western Puerto
Rico in the afternoon. There is a low chance of isolated flash
floods. Elsewhere, plan for water ponding on roads and in poorly
drained areas.

.Excessive Heat...This level of heat affects anyone without
effective cooling and/or adequate hydration, with those sensitive
to heat at the highest risk. Impacts likely in some health
systems, heat-sensitive industries and infrastructures. These
conditions are most likely across urban and coastal areas.

.Rip Currents...Life-threatening rip currents are possible in the
surf zone, particularly across northern Puerto Rico. Isolated
stronger rip currents may occur elsewhere, especially near piers,
jetties, and channels.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Excessive rainfall (Flooding) risk is expected to increase by
midweek with the arrival of a vigorous tropical wave. Dangerous
heat concerns will continue Tuesday and later return by the end of
the week into the weekend. A moderate rip current risk will also
continue most days. By midweek, a wind surge ahead of the tropical
wave may bring locally breezy conditions and choppy seas

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

AMZ716-726-VIZ001-002-230915-
St. Thomas St. John adjacent Islands-St Croix-
Nearshore Atlantic and adjacent Caribbean Coastal Waters-
503 AM AST Mon Sep 22 2025

This Hazardous Weather Outlook is for portions of USVI.

.DAY ONE...Today and Tonight

.Excessive Heat...This level of heat affects most individuals
sensitive to heat, especially those without effective cooling
and/or adequate hydration. Those extremely sensitive to heat face
the highest risk. Some health systems and heat-sensitive
industries could be affected.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Excessive rainfall (Flooding) risk is expected to increase by
midweek with the arrival of a vigorous tropical wave. Dangerous
heat concerns will continue Tuesday and later return by the end of
the week into the weekend. A moderate rip current risk will return
Tuesday and continue most days. By midweek, a wind surge ahead of
the tropical wave may bring locally breezy conditions and choppy
seas.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

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