257
FXCA62 TJSJ 301751
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
151 PM AST Sat Aug 30 2025

.KEY MESSAGES...

* The hot spell is expected to continue through at least early
  next week for the US Virgin Islands and Puerto Rico, with a
  moderate to high chance of issuing an Extreme Heat Warning or
  Heat Advisory each day.

* The risk of rip currents will remain low throughout the Labor
  Day weekend and into at least the middle of next week.

* Strong afternoon thunderstorms will develop each day across
  portions of PR and possibly downwind from the USVI.

&&

.SHORT TERM...Tonight through Monday

Puerto Rico and the US Virgin Islands are still experiencing a
hot spell, with the third consecutive day of Extreme Heat Warnings
for most coastal and urban locations. However, the lingering
tropical moisture, combined with local effects, excessive heating,
and sea breeze variations, promoted the formation of showers and
thunderstorms downwind from the US Virgin Islands, as well as
along and west of the Cordillera Central. The strongest
thunderstorms are producing lightning, torrential rainfall, and
gusty winds. Winds were mainly from the easterly at 10 to 20 mph,
with variations due to sea breezes.

Showers and thunderstorms will continue along the Cordillera
Central, spreading mainly into the southwest as well as across the
north and southern slopes through this evening. Afternoon
convection will also develop mainly downwind from the USVI into
the surrounding waters. Meanwhile, locations without rain will
continue to experience extreme heat; thus, the Extreme Heat
Warnings will continue in effect for both PR and the USVI through
5 PM AST. Please note that we anticipate the hot spell to persist
through the Labor Day Weekend due to the combination of above-
normal maximum and minimum temperatures, above-normal moisture,
and other factors for Puerto Rico and the US Virgin Islands. Thus,
we anticipate elevated to significant Heat Risk levels, which may
increase the likelihood of heat- related illnesses, particularly
for vulnerable populations. We encourage visitors and residents to
stay hydrated, avoid strenuous activity during the hottest part
of the day, never leave children or pets unattended in vehicles,
and wear light, loose, and light- colored clothing.

The above-normal ocean sea surface temperature will enhance the
formation of scattered to numerous showers across the local waters
in the evening, moving inland over the windward locations of PR
and the USVI. The weak tropical wave, now moving westward south of
the islands across the Caribbean Sea, will maintain near-to-
above-normal moisture values for the USVI and PR on Sunday.
Therefore, we expect a mixture of sunshine and clouds tomorrow,
with a typical hydrological pattern consisting of passing showers
across the windward locations, followed by afternoon convection
(with isolated, more robust thunderstorms). As the steering wind
flow will predominantly come from the southeast, these strong
thunderstorms will develop across the northwest quadrant of PR.
The arrival of additional moisture is expected to promote a
similar weather pattern on Monday, characterized by excessive
heating during the day, followed by strong afternoon convection.

.LONG TERM...Tuesday through Saturday...
PREV DISCUSSION.../issued 508 AM AST Sat Aug 30 2025/

No major changes to the long term forecast, a seasonal diurnal
pattern is forecast during the long term period, as patches of
moisture are steered towards the islands under east to east-
southeast steering flow. Weak mid to level troughiness can reach
the area during the second half of the workweek. Precipitable
water (PWAT) values will be at normal values for this time of the
year, with afternoon convective activity reaching values above 2
inches. Current model guidance, suggest PWAT values reaching 2
inches on Saturday, when an easterly disturbance reaches the
islands. Overnight and morning passing showers will continue to
affect the eastern region. Diurnal heating, along with orographic
effects, east to east- southeast steering flow and sea breeze
convergence will promote afternoon showers and t-storm activity,
mainly over the interior to W-NW PR, as well as downwind of El
Yunque and the local islands. Localized heavy downpours,
lightning, and flooding risks will be possible with the afternoon
activity. Per the 2 PM AST Tropical Weather Outlook issued by the
National Hurricane Center, a tropical wave is forecast to emerge
off the west coast of Africa tomorrow, Sunday, and has a low (30%)
formation chance in the next 7 days. With 925 mb temperatures
remaining above normal, up to elevated to possibly significant
heat risk will remain during the workweek. Elevated to significant
heat risks prompt the issuance of Heat Advisories and Extreme
Heat Warnings, respectively. An elevated heat risk affects most
individuals sensitive to heat, especially those without effective
cooling and/or adequate hydration. A significant heat risk affects
anyone without effective cooling and/or adequate hydration. &&

.AVIATION...
(18Z TAFs)

VFR conds will prevail today with occasional VCSH. However,
afternoon (between 17:00 and 23:00 each day) SHRA/TSRA
development across the Cordillera Central and downwind from the
USVI will impact the VCTY of the terminals each day. This will
result in brief periods of MVFR or even IFR conditions, mainly at
TJBQ. Expect winds from the E/ENE at 10-15 kt with higher gusts
and sea breeze variations, becoming calm to light and variable
after 23z. After 31/13z, winds will return from the E/ESE at
around 10-15 kt, which may move the aft SHRA/TSRA near JBQ/JSJ.

&&

.MARINE...

Local effects and sea breeze variations will promote the
development of strong thunderstorms across the western side of
the islands. A weak tropical wave moving across the Caribbean Sea,
and a surface high pressure system across the Atlantic Ocean will
promote moderate easterly winds with moderate chop across the
regional waters through early next week.

&&

.BEACH FORECAST...

The risk of rip currents will remain low in Puerto Rico and the
US Virgin Islands. However, thunderstorms may impact the western
and southwestern regions of Puerto Rico through this evening.

While the overall risk of rip currents is expected to remain low
throughout the forecast period, isolated, stronger rip currents
may occur in certain areas, particularly near piers, jetties, and
channels.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning until 5 PM AST this afternoon for
     PRZ001>003-005-007-008-010>013.

VI...Extreme Heat Warning until 5 PM AST this afternoon for VIZ001-
     002.

AM...None.
&&

$$

MORNING CREW...CAM/MNG
EVENING CREW...ICP/YZR