285
FXCA62 TJSJ 070845
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Sun Sep 7 2025

.KEY MESSAGES...

* An elevated risk of flooding will continue to prevail today
  across much of Puerto Rico as a trade wind perturbation moves
  across the forecast area.

* For the U.S. Virgin Islands, although passing showers and
  thunderstorms may lead to ponding of water on roads today, the
  main hazard is the heat risk with heat indices exceeding 100
  degrees F.

* Across Puerto Rico and the U.S. Virgin Islands, the heat
  indices may briefly meet or exceed 108F today; nevertheless,
  under easterly winds and cloudiness associated with the passing
  perturbation, most of the time must remain below the Heat
  Advisory Criteria.

&&

.SHORT TERM...Today through Tuesday...

An easterly perturbation interacting with a nearby mid to upper
level trough aided in showers and thunderstorms across the regional
waters, and some of them moved inland across the US Virgin Islands
and the north and east coastal sections of PR. Winds were mainly
from the east-southeast at 5 to 10 mph, but locally higher in and
near rain activity. Minimum temperatures finally dropped into the
mid- to upper 70s along the coastal areas, to the low to mid-60s in
the mountains and valleys.

The muggy heat indices will continue today, with maximum values
around 107F or even higher, especially in locations without
sufficient cloud cover or rainfall activity. The proximity of a mid
to upper-level trough and an easterly perturbation will result in an
unstable weather pattern with showers and thunderstorms across the
US Virgin Islands and Puerto Rico today. Although the western and
interior portions of PR will observe little to no rain in the
morning, we anticipate the showers and thunderstorms now affecting
the Virgin Islands and east and north locations of PR moving further
inland into those locations from mid-morning onward. Therefore, the
principal hazards expected for today are thunderstorm activity and
flooding rains. Additionally, during the last few days, we have been
receiving reports of sudden mudslides and landslides across portions
of the interior of PR; thus, any persistent heavy rain across steep
terrains along the Cordillera Central could result in sudden
landslides. Please remain aware of your surroundings and understand
the risk for your community.

Above-normal tropical moisture will continue to move across the
region on Monday. This moisture, combined with the warmer-than-
normal sea surface temperatures, will aid in the formation of
scattered to numerous showers across the regional waters overnight
and early Monday morning. This activity will move inland across the
US Virgin Islands and the windward locations of PR occasionally. The
muggy heat indices will continue on Monday, and maximum heat indices
will remain in the mid-100s or near 110 degrees Fahrenheit in the
afternoon. The combination of the diurnal heating, the moisture
content, local effects, and sea breezes will give place to another
round with strong thunderstorms by Monday afternoon. However, a
relatively drier air mass could slowly decrease the coverage of the
most intense activity by Monday evening into Tuesday. This drier air
mass will arrive across the region with low concentrations of
Saharan dust particles. However, the typical hydrological pattern
involves AM passing showers across the windward locations, followed
by strong afternoon convection across the western locations, due to
various factors, such as excessive heating.

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

A weakening in the mid-level ridge pattern is expected early in
the cycle as trofiness develops northeast of the local islands.
However, by the end of the cycle, the mid-level ridging will
return. At lower levels, a surface high pressure will prevail
across the tropical Atlantic, promoting east- southeast winds.
Based on the latest grand ensemble, precipitable water is expected
to remain above 2.0 inches from Wednesday through Friday, with a
sharp decrease anticipated over the upcoming weekend as the
developing mid-level ridge erodes the available moisture. The
highest values of precipitable water early in the forecast cycle
coincide with the passage of a tropical wave (former Invest 91L)
currently located near the 40W.

Under this evolving pattern, the highest chance of showers and
thunderstorms is expected on Wednesday and Thursday, with a
transition on Friday and into the weekend. Having said this, the
intensity and coverage of showers and thunderstorms are expected
to decrease by the end of the workweek, resulting in a more
seasonal pattern with afternoon showers and thunderstorms
primarily focused on the western areas of Puerto Rico. As a
result, the flooding risk remains elevated throughout the forecast
period, decreasing somewhat by the upcoming weekend.

Maximum temperatures will continue to range in the upper 80s to
mid 90s with heat indices exceeding 100 degrees F under the
prevailing east southeast wind flow. Therefore, the heat risk
will remain elevated for much of the forecast cycle. Some
haziness is anticipated Wednesday and Thursday.

&&

.AVIATION...
(06Z TAFS)

Brief reductions in VIS/CIGs due to SHRA/TSRA are possible across
JSJ/IST/ISX through this afternoon, resulting in brief MVFR/IFR.
Then SHRA/TSRA will spread into the interior and W-PR btwn 07/15-
23z, affecting JPS/JBQ. Expect calm to light/VRB winds thru 07/13z.
Aft 07/13Z, winds will return from the ESE at 10-15 kt but locally
higher in and near TSRA. Streamer downwind from the USVI or El
Yunque could also affect ISX/IST and TJSJ, respectively.

&&

.MARINE...

A surface high pressure across the Central Atlantic will promote
moderate to locally fresh easterly winds, resulting in moderate chops
through the middle of the week. An easterly perturbation will
continue to promote showers and thunderstorms across the regional
waters today and tomorrow. Then, a tropical wave is expected to move
near the islands around Wednesday, increasing local winds and
potentially triggering showers and thunderstorms again.

&&

.BEACH FORECAST...

A low risk of rip currents will continue to prevail across all
shorelines. Nevertheless, isolated stronger rip currents may
occur in the vicinity of groins, jetties, reefs, and piers.
Beachgoers must also stay aware of the weather conditions across
the area, particularly in the afternoons and evenings, due to
thunderstorm activity that may approach the surf zone. Beachgoers
must leave the water and seek shelter if thunderstorms are close
by.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION/MARINE...CAM
LONG TERM/BEACH FORECAST....OMS