703
FXCA62 TJSJ 311801
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
201 PM AST Sun Aug 31 2025

.KEY MESSAGES...

* The heat spell is expected to continue this week, with a high
  likelihood of issuing an Extreme Heat Warning or Heat Advisory
  each day.

* The risk of rip currents will remain low through at least Friday
  for most beaches in Puerto Rico, and through Friday for the US
  Virgin Islands, when the risk is forecast to become moderate for
  the exposed beaches of St. Croix.

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

&&

.SHORT TERM...Tonight through Tuesday...

Today we issued the fourth consecutive day of Extreme Heat
Warnings for most coastal and urban locations. Thus, Puerto Rico
and the US Virgin Islands are still experiencing a heat spell,
primarily due to the above-normal moisture content, southwesterly
wind flow, and above-normal temperatures along the islands and
surrounding waters. That same available moisture, combined with
local effects, excessive daytime heating, and sea breeze
variations, promotes the formation of showers and thunderstorms
downwind from La Sierra de Luquillo and the US Virgin Islands, as
well as along and west of the Cordillera Central. The strongest
thunderstorms resulted in frequent lightning, torrential rainfall,
and gusty winds. Winds were mainly from the easterly at 10 to 20
mph, with variations due to sea breezes.

The east-southeasterly steering wind flow will promote the
development of additional showers and thunderstorms along and to
the north and west of the Cordillera Central, as well as downwind
from La Sierra de Luquillo. Additionally, afternoon activity will
develop downwind from the US Virgin Islands, spreading mainly
into the surrounding waters. Meanwhile, the US Virgin Islands and
PR`s southern coast, as well as locations without significant
rain, will continue to experience extreme heat; thus, Extreme Heat
Warnings will remain in effect for both PR and the US Virgin
Islands through 5 PM AST. Rain activity will significantly
diminish overnight, leaving calm weather conditions, but with
warmer-than-normal minimum temperatures across the region.

Please be advised that the ongoing heat spell is expected to
persist through at least the middle of the week, especially in
urban and coastal areas of Puerto Rico and the US Virgin Islands.
This is supported by above-normal maximum temperatures at 925 MB,
which model guidance suggests are values more than two standard
deviations above the TJSJ 30-year climatology. Additional
ingredients include above-normal daytime and nighttime
temperatures, elevated moisture levels, and the weak east-
southeasterly winds. As a result, we anticipate a Heat Risk to
fluctuate between elevated and significant, which could increase
the chances of heat-related illnesses, especially among vulnerable
groups. We urge both residents and visitors to stay well-
hydrated, limit strenuous activities during peak heat hours, avoid
leaving children or pets inside vehicles, and wear lightweight,
loose-fitting, light-colored clothing.

The weather pattern for the upcoming nights will be influenced by
above-normal sea surface temperatures, which will lead to the
formation of scattered to numerous showers across the local
waters. These showers will then move inland to affect the windward
areas of PR and the USVI. During the day, we can expect a mix of
sunshine and clouds, with passing showers in the windward
locations, followed by afternoon convective activity. This
afternoon`s activity will be intensified by incoming surges of
moisture, excessive daytime heating, variations in the sea breeze,
and local effects, resulting in frequent lightning, heavy
downpours, and gusty winds.


.LONG TERM...Wednesday through Sunday...

A seasonal diurnal pattern is forecast during the second half of
the workweek, as patches of moisture are steered towards the
islands under east to east- southeast steering flow and weak mid
to upper-level troughiness moves over the area. 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 suggests widespread PWAT values
reaching 2 inches during the weekend. A tropical wave will reach
the islands on Saturday and its moisture will linger during the
weekend. Current model guidance also suggests, an upper level low
will also moving northeast of the islands late Saturday and
Sunday. Overnight and morning passing showers will continue to
affect the eastern region. Along with the above mentioned
features, diurnal heating, 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 August 31st 2 PM AST Tropical Weather Outlook issued by
the National Hurricane Center, a tropical wave is now moving
westward from the west coast of Africa, 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 period.
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 SHRA/TSRA will develop along the Cordillera Central,
NW- PR, and downwind from the USVI with VCTY near
JSJ/JPS/JBQ/ISX/IST. JBQ will have periods of MVFR or even brief
IFR conditions through 31/23z. We are forecasting a similar
pattern for tomorrow. Expect ESE winds at 10-15 kt with higher
gusts and sea breeze variations, becoming calm to light and
variable after 23:00, similar to today after 01/13z.


&&

.MARINE...

A tropical wave moving away into the central Caribbean, a surface
high pressure across the Central Atlantic, and a frontal boundary
across the western Atlantic will promote an east-southeast
moderate wind flow across the islands through at least the middle
of the week. Afternoon thunderstorms will develop each day across
the western coastal waters of Puerto Rico and downwind from the US
Virgin Islands.

&&

.BEACH FORECAST...

The risk of rip currents will remain low in Puerto Rico and the
US Virgin Islands through at least Friday, when we forecast a
moderate risk of rip currents for the exposed beaches of St.
Croix. Be aware that thunderstorms may impact the western and
northern regions of Puerto Rico through this evening.

Although the overall risk of rip currents is expected to remain
low during the forecast period, isolated but stronger rip currents
may occur in specific areas, especially near piers, jetties, and
channels.

&&

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

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

AM...None.
&&

$$

SHORT TERM...MNG
LONG TERM....YZR
AVIATION...ICP