471
FXCA62 TJSJ 291947
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
Issued by National Weather Service Miami FL
347 PM AST Fri Aug 29 2025

.KEY MESSAGES...

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

* We expect a low risk of rip currents throughout the Labor Day
  weekend.

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

&&

.SHORT TERM...

Hot heat indices prevailed across some urban and coastal sections
of PR and the USVI throughout the morning and afternoon hours.
However, the trailing tropical moisture, combined with local effects,
excessive heating, and sea breeze variations, promoted the formation
of showers and thunderstorms downwind from El Yunque into Trujillo
Alto, Carolina, and San Juan. Then, a cluster of strong thunderstorms
developed across the interior, west, and north-central locations of
Puerto Rico, producing frequent lightning, torrential rainfall, and
gusty winds. Winds were mainly from the east-southeast at 10 to 20
mph, with variations due to sea breezes.

Showers and thunderstorms will continue along the Cordillera Central
and western PR through this evening, and some locations will have a
limited to elevated chance of flooding rain. However, locations
without rain will experience extreme heat; thus, the Extreme Heat
Warning and Heat Advisory will continue in effect for PR and the USVI
through 5 PM AST. The above-normal ocean sea surface temperature will
enhance the formation of scattered to numerous showers across the local
waters, moving inland over the windward locations of PR and the USVI.
A similar weather pattern is expected to prevail tomorrow (Saturday),
with excessive heating during the day, followed by strong afternoon
convection.

We expect a mixture of sunshine and clouds on Sunday and Monday, with
a typical hydrological pattern consisting of passing showers across
the windward locations, followed by afternoon convection across western
PR and downwind from the US Virgin Islands.

The hot spell will continue through the Labor Day Weekend, impacting
lower elevations and urban areas of Puerto Rico, as well as the US
Virgin Islands, Vieques, and Culebra. Elevated to Significant Heat
Risk levels are expected, 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.

.LONG TERM...

A seasonal diurnal pattern is forecast during the workweek to
start September, 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 values will be at normal values for
this time of the year, with afternoon convective activity reaching
values above 2 inches. Overnight passing showers will also
affect the eastern region. With 925 mb temperatures remaining
above normal, elevated to possibly significant, at times, 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. This
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
this Sunday and has a low (30%) formation chance through 7 days.

&&

.AVIATION...
(18Z TAFS)

Mainly VFR conditions across most TAF sites, with the exception of
TJBQ that have TSRA and VCTS. As a result, MVFR to intermittent IFR
likely through at least 29/22-23Z. Sfc winds bcmg light and variable
after 29/23Z. VCSH is possible during the overnight period across USVI
TAF sites and TJSJ. After 30/13Z, E winds at 10 to 15 kt with sea
breeze typical variations followed by VCTS and TSRA after 30/16Z
across the interior, western PR, and downwind from the USVI.

&&

.MARINE...

The lingering tropical moisture near PR and the USVI will promote
showers and thunderstorms each afternoon. Another weak tropical
wave will enter the Lesser Antilles by Saturday. Mariners can
expect moderate east to east-southeast winds and moderate chops
across the regional waters the rest of the weekend into early
next week.

&&

.BEACH FORECAST...

The risk of rip currents will remain low in PR and the US Virgin
Islands. However, keep in mind that thunderstorms could also
impact the northwest quadrant of PR through this evening. The
risk of rip currents is expected to be low throughout the
forecast period. However, isolated stronger rip currents may
occur elsewhere, especially near piers, jetties, and channels.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning until 5 PM AST this afternoon for
     PRZ001>005-007-008-010-011.

     Heat Advisory until 5 PM AST this afternoon for PRZ012-013.

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

AM...None.
&&

$$

SHORT TERM...SJU
LONG TERM....SJU
AVIATION...SJU