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235
FXCA62 TJSJ 110728
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
328 AM AST Fri Sep 11 2026

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

.KEY MESSAGES...
Issued at 328 AM AST Fri Sep 11 2026

- Dense Saharan dust will remain the dominant feature today and
  Saturday, with high to locally very high concentrations. This
  will result in hazy skies, reduced visibility, and deteriorated
  air quality.

- Warm to hot conditions will continue, with an elevated to
  significant heat risk most days. Today, from 10 AM to 5 PM, an
  Excessive Heat Warning will be in effect for Puerto Rico, and a
  Heat Advisory will be in effect for the USVI, Vieques and
  Culebra.

- Increasing shower and thunderstorm activity is expected Sunday,
  especially across western Puerto Rico.

- 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(Today through Sunday)...
Issued at 328 AM AST Fri Sep 11 2026

alm conditions were experienced over the islands as a dense
Saharan Air Layer (SAL) continued to filter in. Lows were in the
upper 70s to low 80s across urban and lower elevation areas of
Puerto Rico, in the low 80s across Vieques, Culebra and the USVI,
and in the 60s to low 70s across higher elevations of Puerto Rico.

The dense SAL will be the dominant feature today as it continues
to move over the islands. High concentrations, locally very high
at times, of Saharan Dust will continue to spread over the islands
today and tomorrow, Saturday. These high concentrations of
Saharan Dust will result in hazy skies, reduced visibility, and
deteriorated air quality. Individuals in sensitive groups, such as
those with respiratory conditions, young children, and older
adults, should take appropriate precautions, follow health
officials` recommendations, and limit prolonged outdoor exposure.
Saharan dust concentrations are forecast to gradually decrease
late Saturday night into the overnight hours on Sunday as the SAL
moves westward and out of the region. Current guidance suggests
that moderate concentrations should move out of the region by
early Sunday morning with low concentrations thereafter.

Warm to hot conditions (particularly each late morning to afternoon)
are expected at least through the rest of the week as the drier
and hazier pattern continues; an elevated to significant heat risk
will be present over the islands. From 10 AM to 5 PM AST, today,
an Excessive Heat Warning will be in effect for Puerto Rico
(particularly across coastal and urban areas and lower-elevation
valleys) and a Heat Advisory will be in effect for St. Thomas, St.
John, St. Croix, Vieques and Culebra. Follow health officials`
recommendations, stay hydrated, stay in an air-conditioned room if
possible and stay in the shade. Overnight heat trapping by the
Saharan Dust will also result in warmer lows tonight and Saturday
night.

Breezy conditions will prevail through the weekend especially along
coastal and exposed areas, due to a surface high pressure north
of the islands. The steering flow, however, will vary throughout
the short term period: today will start with an ESE flow but will
gradually back as the day continues becoming E by Saturday and ENE
by Saturday afternoon. Steering flow is then forecast to veer and
become more E by Sunday and ESE once again by Sunday afternoon.
These winds can steer brief passing showers over windward sectors.
Diurnal heating, sea breeze convergence, local orographic effects
and available moisture can also result in showers over portions
of interior and western Puerto Rico each afternoon. However, the
SAL will serve to suppress deep convection today and Saturday. An
upper-level trough, however, will start to approach the islands
later today and persist mainly north and northwest of the islands
through the rest of the short term period. This feature may
slightly increase the potential for showers. By Sunday however,
with Saharan dust concentrations decreasing to low, available
moisture increasing, the upper trough still near the region and a
weak tropical wave is moving mainly south of the islands, the
potential for showers and t-storms further increases especially
during afternoon convection. 500 mb temperatures are forecast to
cool to around -8 C and precipitable water (PWAT) is forecast to
increase to more seasonal values. Due to this, at least a limited
flooding risk over sectors of western Puerto Rico is forecast
during the afternoon hours.

&&

.Long Term(Monday through Friday)...
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...
(06Z TAFS)
Issued at 328 AM AST Fri Sep 11 2026

Mainly VFR conditions. High concentrations of Saharan dust will
result in HZ and VIS at generally 6SM, with brief reductions to
5SM possible. -SHRA possible over TJBQ btwn 11/17-20z. Winds up to
around 5 kts, through 11/13z, then ESE at up to around 15 to 20
kt, with sea breeze variations and stronger gusts.

&&

.MARINE...
Issued at 328 AM AST Fri Sep 11 2026

A strengthening surface high pressure across the central Atlantic
will continue to promote moderate to fresh winds today and
through the weekend. These winds will maintain choppy marine
conditions, with seas generally around 4 to 5 feet, occasionally
reaching 6 feet across most local waters and Caribbean passages.
High concentrations of Saharan dust particles will likely remain
across the region today through at least Saturday night, resulting
in hazy skies and reduced visibility. Isolated showers may move
across the waters at times, but the drier airmass will generally
limit widespread shower development through Saturday, with rain
chances increasing by the end of the weekend into early next
week.

&&

.BEACH FORECAST...
Issued at 328 AM AST Fri Sep 11 2026

Today, a moderate risk of rip currents persists along the
northern, eastern, and southeastern beaches of Puerto Rico, as
well as in Culebra, Vieques, and the U.S. Virgin Islands. A
moderate risk means that life-threatening rip currents are
possible, and beachgoers are urged to exercise caution. A low risk
is present across the western and more protected beaches of
Puerto Rico. However, life-threatening rip currents can still
occur when the risk is low, particularly near groins, jetties,
reefs, and piers. Similar conditions are expected to prevail
through at least Sunday. Afterward, the risk will slightly
decrease in area, but the moderate risk will likely persist along
exposed northern beaches.

From today through at least late Saturday, high concentrations of
Saharan dust particles will be present across the region,
resulting in hazy skies, reduced visibility, and poor air quality
for outdoor activities. Heat will also remain an additional
concern over the coming days. Beachgoers should stay hydrated and
limit prolonged sun exposure.

&&

.FIRE WEATHER...
Issued at 328 AM AST Fri Sep 11 2026

Despite recent wetting rains in southern Puerto Rico, elevated
KBDI values demonstrate that deeper soil and fuel layers remain
dry. The combination of breezy ESE winds and incoming drier air
will maintain a low-to-moderate fire danger risk across these
areas today, though localized spikes in threat levels remain
possible. We will closely monitor evolving weather patterns and
fuel moisture trends for any potential escalation in fire risk.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning from 10 AM this morning to 5 PM AST this
     afternoon for PRZ001>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.
&&

$$

KEY MESSAGES...KML
SHORT TERM/AVIATION/FIRE WEATHER...MRR/KML
LONG TERM....MNG/JCP
MARINE/BEACH FORECAST...YZR

NWS SJU Office Area Forecast Discussion