753
FXCA62 TJSJ 300908
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Sat Aug 30 2025

.KEY MESSAGES...

* The US Virgin Islands and Puerto Rico will observe a hot spell
  throughout the rest of the Labor Day Weekend, with a moderate
  to high chance of issuing an Extreme Heat Warning or Heat
  Advisory each day.

* Today, an Extreme Heat Warning will be in effect from 10 AM
  through 5 PM for the coastal and urban areas of Puerto Rico. A
  Heat Advisory will also be in effect today from 10 AM through 5
  PM for the US Virgin Islands, Vieques, and Culebra.

* A low risk of rip currents is expected today, during the rest of
  the Labor Day weekend and possibly through midweek, across all
  beaches of PR and the USVI.

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

&&

.SHORT TERM...Today through Monday...

During the overnight hours, tranquil weather prevailed across Puerto
Rico and the U.S. Virgin Islands. However, after 2 AM, frequent
pockets of showers developed over the surrounding waters, with some
moving into the northern and northeastern municipalities of Puerto
Rico, as well as Vieques, Culebra, and the U.S. Virgin Islands.
Rainfall accumulations ranged from 0.10 to 0.40 inches. Winds
remained light, generally from the east-northeast, while
temperatures stayed in the mid-to-upper 70s along coastal areas and
in the 60s to low 70s across the mountainous areas.

As in previous days, today we anticipate a mix of sunshine and
periods of cloud cover. This will allow the ongoing hot spell to
persist across the islands. Elevated to significant heat risk levels
are forecast particularly in urban and coastal areas where Extreme
Heat Warnings are in effect for Puerto Rico from 10:00 AM to 5:00
PM. Heat Advisories are also in place for Vieques, Culebra, and the
U.S. Virgin Islands during the same time frame. These conditions
increase the likelihood of heat-related illnesses, particularly for
vulnerable populations. Residents and visitors are strongly advised
to stay well hydrated, wear light and loose-fitting clothing, avoid
strenuous outdoor activities during peak heating hours, and never
leave children or pets unattended in vehicles. By the afternoon,
showers and thunderstorms are likely to develop, mainly across the
interior, western, and southwestern sections of Puerto Rico, and
possibly over the San Juan metro area. This activity will be
supported by moisture associated with a tropical wave located to the
south of the region. Model guidance indicates precipitable water
values between 1.60 and 1.80 inches, along with mid-level
temperatures ranging from -8 to -7 degrees Celsius, which will
enhance instability. While these showers may provide brief relief,
hot and humid conditions will otherwise persist through the Labor
Day weekend. Updates will continue to be issued as necessary to
keep residents and visitors well-informed and safe during this
prolonged hot spell.

By the beginning of September, a seasonal diurnal pattern is
forecast with patches of moisture steered towards the islands and
the regular afternoon convection.

.LONG TERM...Tuesday through Saturday...

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 AM 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...
(06Z TAFs)

All TAF sites should experience VFR conditions. However, SHRA/TSRA
associated with the afternoon convection is expected. This will
allow brief periods of MVFR cond from 30/17-23Z at TJBQ, TJPS, and
TJSJ. E winds will dominate all sites, increasing in speed from
30/13Z to around 3 to 15 kts. However, we anticipate occasional
higher gusts, with the heaviest rainfall. Sfc winds will bcmg light
after 23Z.

&&

.MARINE...

Moderate easterly winds will prevail over the next few days.
Conditions should remain favorable for small craft. However, strong
thunderstorms will continue to affect the coastal waters of western
Puerto Rico during the afternoon hours. A weak tropical wave will
enter the eastern Caribbean today, increasing the potential for
showers and thunderstorms.

&&

.BEACH FORECAST...

The risk of rip currents will remain low through the weekend, and
possibly extending through the next midweek. Even if the risk of
rip currents is low, life-threatening rip currents often occur in
the vicinity of groins, jetties, reefs, and piers.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning from 10 AM this morning to 5 PM AST this
     afternoon for PRZ001>003-005-007-008-010-011.

     Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ012-013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...MMC
LONG TERM....MRR