778
FXCA62 TJSJ 111753
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
153 PM AST Fri Sep 11 2026

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

.KEY MESSAGES...
Issued at 105 PM AST Fri Sep 11 2026

- A deep Saharan Air Layer (SAL) continues to bring high concentrations
  of Saharan Dust. Tease conditions are expected to persist well
  into Sunday morning.

- An Extreme Heat Warning for mainland Puerto Rico and Heat
  Advisory for the US Virgin Islands, Culebra, and Vieques remains
  in effect until 5 PM today. Therefore, people should limit
  outdoor activities and remain hydrated.

- A low pressure system at high levels will settle to the
  north/northwest of the forecast region. Conditions are expected
  to become more favorable for the development of localized
  convection, especially over the interior and western regions of
  Puerto Rico. Flooding threat remains limited.

- Breezy conditions will prevail through the weekend, especially
  along coastal and exposed areas.

- Moderate rip current risk expected today along the northern,
  eastern and southeastern beaches of Puerto Rico, Vieques,
  Culebra and the U.S. Virgin Islands.

&&

.Short Term(This evening through Sunday)...
Issued at 105 PM AST Fri Sep 11 2026

Hazy skies, reduced visibility, and deteriorated air quality
prevailed today as a Saharan Air Layer (SAL) continues to filter
into the region bringing high concentrations of dust to the US
Virgin Islands and Puerto Rico. Conditions remain
thermodynamically unfavorable for the development of deep
convection as a the thick SAL is leading to a strong inversion
near 800 millibars. One of the main concerns for the rest of today
is the Significant Heat Risk for mainland Puerto Rico and
Elevated Heat Risk for the US Virgin Islands, Vieques and Culebra.
With heat indices ranging between 100 to a 112 degrees Fahrenheit
across the coastal and urban sectors of Puerto Rico, and 85-90
along the interior of Puerto Rico. Thus, an Extreme Heat Warning
(Puerto Rico) and a Heat Advisory (US Virgin Islands, Vieques and
Culebra) remains in effect until 5 PM today. Consequently, the
potential for the development of showers remains limited for
today.

Similar weather conditions will prevail through early Sunday, as
high concentrations of Saharan Dust will persist over the region.
Individuals in sensitive groups, such as those with respiratory
conditions, young children, and older adults, should take
appropriate precautions, limit prolonged outside activities and
follow the recommendations of health officials. With limited cloud
cover and enhanced SAL, heat conditions are forecasted to persist
for the rest of the short term period. While the heating is
expected mainly during the daytime, nighttime minimums are also
expected to be higher than usual due to radiative effects caused
by the Saharan Dust which will limit nighttime cooling.

Conditions are expected to shift to a more humid seasonal pattern
by Sunday morning as the SAL leaves the County Warning Area(CWA)
and an upper level low pressure settles into the region. This
pattern will be more favorable for the development of convection,
especially across the interior and western regions of Puerto Rico.
Nonetheless, model guidance suggests that deep convection might
remain limited and localized due to a drier mid level air
intrusion and remnants of the SAL.

&&

.Long Term(Monday through next Thursday)...
Issued at 328 AM AST Fri Sep 11 2026

A surface high pressure will continue to promote easterly-
southeasterly breezy winds for most of the period. Variable
conditions are expected from Monday morning until Tuesday morning,
due to a drier slot in the mid levels, lowering PWAT values
(between 1.2 and 1.4 inches, isolated areas up to 1.6 inches).
Nevertheless, the proximity of an upper-level low could increase
instability and enhance deeper convection in the area. Therefore,
showers and thunderstorms during the afternoon hours could lead to
ponding of water over roadways and poorly drained areas,
including the possibility of urban and small stream flooding over
western Puerto Rico. By Tuesday, moisture associated with a
tropical wave is expected to approach the local area by Tuesday
afternoon, enhancing shower activity once again across western
portions of Puerto Rico, with a limited flooding risk. On
Wednesday, as the upper-level low departs the region and a mid-to-
upper level ridge approaches the eastern Caribbean, lingering
moisture will still bring passing showers across windward sections
of the islands during the morning, with afternoon convection
across interior and northwestern Puerto Rico. By Thursday, another
tropical wave is forecasted to reach the islands, as the latest
model guidance suggest an increase in moisture content (PWAT
values between 1.9 and 2.1 inches). Nevertheless, there`s
uncertainty regarding the time of arrival of this feature, as the
latest ECMWF suggest the arrival by early Thursday, while the GFS
suggests it could reach the area a bit later (Thursday afternoon
and evening). Therefore, expect shower and thunderstorm activity,
though the flooding threat could vary depending on the timing of
the tropical wave.

Under a easterly-southeasterly wind flow, warmer conditions can
be expected throughout the long-term period, particularly by the
beginning of the next workweek. With abundant tropical moisture,
heat indices are very likely to exceed 100 degrees Fahrenheit,
increasing the heat risk. Therefore, a limited to elevated heat
threat is expected across the islands, and heat products may be
issued if required; please continue to monitor the forecast for
any updates.

&&

.AVIATION...
(18Z TAFS)
Issued at 105 PM AST Fri Sep 11 2026

VFR conds will prevail. Saharan dust will maintain HZ and VSBY
around 6SM at all terminals through the period. E-ESE winds 15-20 kt
with gusts 23-28 kt will continue through this aftn, strongest at
TJPS/TJBQ. Winds will diminish after 22-23Z, then increase again
after 12/15Z with gusts 23-27 kt.

&&

.MARINE...
Issued at 105 PM AST Fri Sep 11 2026

The pressure gradient between a strengthening ridge north of the
region and the Colombian low will maintain moderate to fresh
easterly winds tonight and through the weekend, with the strongest
winds across the Caribbean waters and passages. These winds will
result in choppy seas of 4 to 5 feet, occasionally up to 6 feet.
Small craft should exercise caution. Saharan dust will continue
through Saturday night, limiting shower activity and reducing
visibility. Moisture will increase late in the weekend into early
next week, favoring an increase in shower activity.

&&

.BEACH FORECAST...
Issued at 105 PM AST Fri Sep 11 2026

A moderate risk of rip currents will continue along the northern,
eastern, and southeastern beaches of Puerto Rico, as well as
Culebra, Vieques, and the U.S. Virgin Islands through the weekend.
Life-threatening rip currents remain possible in these areas, while
a low risk is expected along western and more protected beaches.
However, dangerous rip currents can still occur near groins,
jetties, reefs, and piers.

Saharan dust will continue to promote hazy skies and reduced
visibility through at least Saturday night. An increase in shower
and thunderstorm activity is expected late Sunday into early next
week, particularly across western Puerto Rico. Beachgoers should
remain alert for lightning and rapidly changing weather conditions,
and seek shelter if thunderstorms approach.

&&

.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...RVT/MMC/CVB
LONG TERM...MNG/JCP
AVIATION/MARINE/BEACH FORECAST...CVB