559
FXCA62 TJSJ 101840
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
240 PM AST Thu Sep 10 2026

...New SHORT TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 212 PM AST Thu Sep 10 2026

- The main risk for the day remains the elevated to significant
  extreme heat risk. Thus a Heat Advisory is in effect for the US
  Virgin Islands, Vieques and Culebra. Whereas a Extreme Heat
  Warning is in effect for mainland Puerto Rico. These conditions
  are expected to persist throughout the rest of the short term
  period as a drier pattern settles in.

- Moderate concentrations of Saharan Dust have gradually filtered
  into the forecast region and will increase to high
  concentrations later tonight into Friday morning, with the
  highest concentrations are expected on Friday.

- Passing showers will develop over western Puerto Rico this
  afternoon,while additional showers are forecast to mover over
  the US Virgin Islands and the eastern half of PR during the
  overnight hours.

&&

.Short Term(This evening through Saturday)...
Issued at 212 PM AST Thu Sep 10 2026

A weak tropical wave moved across the region, increasing TPW values
to around 2 inches across Puerto Rico and the U.S. Virgin
Islands. Elevated moisture combined with ESE winds supported
showers and thunderstorms across southeastern, northeastern, and
interior Puerto Rico, as well as the U.S. Virgin Islands. Radar
estimates indicate rainfall accumulations of 2 to 4 inches across
portions of Cayey, Barranquitas, and Guayama, with 1 to 1.5 inches
observed elsewhere across eastern, northern, and interior Puerto
Rico. A Flood Advisory for those municipalities was extended
through 7:30 AM AST due to the ongoing potential for flooding. As
morning convection diminished, heat indices of 100 to 108 degrees
Fahrenheit prevailed across the U.S. Virgin Islands, Vieques, and
Culebra where a Heat Advisory was issued. Across mainland Puerto
Rico, a significant heat risk will prevail, with heat indices
above 112 degrees Fahrenheit where the Extreme Heat Warning
remains in effect.

For the remainder of today into tonight, passing showers may
affect eastern and northwestern Puerto Rico amid moderate
concentrations of Saharan dust. As the tropical wave exits, a
drier air mass associated with moderate to high concentrations of
Saharan dust will spread across the region. The resulting Saharan
Air Layer (SAL) will suppress deep convection, with the highest
dust concentrations expected from Friday night into Saturday
morning. Generally dry conditions will persist through the
remainder of the short-term period. However, an upper-level trough
north of the forecast area may slightly increase the potential for
isolated showers on Saturday. Limited cloud cover and drier
conditions will also favor elevated heat risk Friday and Saturday,
particularly across urban and coastal areas. Residents and
visitors should follow guidance from health officials, limit
outdoor activities, and remain adequately hydrated.

&&

.Long Term(Sunday through next Wednesday)...
Issued at 420 AM AST Thu Sep 10 2026

The surface high-pressure will continue to promote easterly
breezy winds across the islands for most of the forecast period.
From Saturday night, dust concentrations are expected to diminish
as a result of the Saharan Air Layer (SAL) exiting the area.
Precipitable water values (PWAT) will briefly reach seasonal
values on Sunday and Monday morning, varying between 1.75 to 2.00
inches.

Current model guidance shows a drier air slot moving across the area
on Monday afternoon. These drier conditions will persist until
Tuesday afternoon, with PWAT values returning to seasonal values by
the evening and exceeding two inches by the end of the workweek. A
tropical wave is expected to approach the islands following the
aforementioned drier air slot. A more robust wave, is anticipated to
reach the islands from Thursday night into Friday.

The transition to wetter conditions supported by daytime heating,
local effects and the consecutive tropical waves over the CWA could
bring an increase to the chance of showers and thunderstorms across
the islands, especially through the end of the workweek. This could
potentially trigger an elevated flood risk across portions of the
islands. We advice residents and visitors to continue monitoring the
forecast as adjustments and updates become available.

&&

.AVIATION...
(18Z TAFS)
Issued at 212 PM AST Thu Sep 10 2026

Mainly VFR thru the period. E-ESE winds 14-16 kt with frequent gusts
23-27 kt expected at all terminals, strongest during the afternoon.
Saharan dust will maintain HZ with VIS generally 6SM, with brief
reductions to 5SM possible.

&&

.MARINE...
Issued at 212 PM AST Thu Sep 10 2026

A strengthening surface high pressure across the central Atlantic
will continue to promote moderate to fresh winds, with locally
strong winds and stronger gusts at times, through the next few days.
These winds will maintain choppy to locally rough marine conditions,
with seas generally around 5 to 6 feet across most waters and local
passages, and occasionally up to around 8 feet across the offshore
Atlantic waters. Periods of stronger winds and higher seas will
remain possible, particularly across exposed waters and passages.
Moderate to high concentrations of Saharan dust will also persist
across the region during the next few days, resulting in hazy skies
and reduced visibility at times. Isolated to scattered showers may
move across the waters, but Saharan air will generally limit
widespread shower development.

&&

.BEACH FORECAST...
Issued at 212 PM AST Thu Sep 10 2026

There is a moderate risk of rip currents along most beaches of
Puerto Rico and the U.S. Virgin Islands today. Breezy to windy
conditions are expected to persist through the next few days, with
life-threatening rip currents possible. Beachgoers are urged to
exercise caution, especially at beaches without lifeguards.

Moderate to high concentrations of Saharan dust will persist across
the region, resulting in hazy skies and reduced visibility at times.
Isolated to scattered showers remain possible, but Saharan air will
generally limit widespread shower development. Heat will remain an
additional concern, and beachgoers should remain hydrated and limit
prolonged sun exposure.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning until 5 PM AST this afternoon for
     PRZ001>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...MMC/RVM
LONG TERM...JCP
AVIATION/MARINE/BEACH FORECAST...CVB