397
FXCA62 TJSJ 101756
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
156 PM AST Mon Aug 10 2026

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

.KEY MESSAGES...
Issued at 150 PM AST Mon Aug 10 2026

- Warm to hot conditions will continue this workweek across the
  islands, particularly over urban and low-lying areas. The Heat
  Advisory remains in effect through 4:00 PM AST.

- Frequency of showers and isolated thunderstorms will likely increase
  early Tuesday, increasing flood and lightning potential.

- Marine and coastal conditions may deteriorate by the end of the workweek
  into the weekend as stronger trade winds build seas and
  increase the rip current risk.

- The NOAA NHC continues to monitor multiple Atlantic
  disturbances; it remains too early to determine any impacts to
  Puerto Rico or the U.S. Virgin Islands.

&&

.Short Term(This evening through Wednesday)...
Issued at 150 PM AST Mon Aug 10 2026

An elevated heat threat alongside fluctuating moisture and Saharan
dust concentrations will dominate the short-term forecast period.
Upper-air atmospheric soundings and satellite observations
indicate precipitable water values fluctuating between 1.50 and
1.80 inches, capped somewhat by weak mid-level lapse rates around
5.0 to 5.5C/km and a persistent low-level trade wind inversion.
Strong solar heating pushed temperatures into the upper 80s to
mid-90s across the lower elevations today. This, combined with
enough surface moisture, increased heat indices between 106112F
along coastal and urban zones. A Heat Advisory remains in effect
across low-lying terrain of all islands. The heat threat will
persist for the next few days, and warmer 925mb temps are expected
on Wednesday, and an Excessive Heat Warning could be required.

In terms of precipitation, it will vary noticeably over the next
72 hours. Drier air and Saharan dust following a departing
tropical wave will limit convective coverage today to isolated
diurnal afternoon showers over western Puerto Rico. However,
latest global model guidance and high-resolution ensemble show a
tropical wave with a surge in moisture crossing the local region
on Tuesday, raising precipitable water levels near 2.00 inches.
Strong daytime heating, sea breeze convergence, and terrain-forced
uplift interacting with this tropical moisture will trigger and
increase the coverage of showers and thunderstorms on Tuesday
afternoon. The strongest cells will be capable of producing
frequent cloud-to-ground lightning, gusty winds, and localized 1
to 2-inch rainfall accumulations, creating a heightened potential
for ponding of water on roads and minor urban or small-stream
flooding across the interior and western Puerto Rico.

By Wednesday, aerosol guidance and normalized moisture anomaly
fields indicate a slot of drier, dust-laden Saharan air
overspreading the region behind the departing wave. Precipitable
water values will drop back below seasonal averages, capping
widespread deep convection and restricting shower activity to
brief passing early morning trade showers across windward areas
and isolated afternoon convection along the western mountains.
Pulses of suspended Saharan dust will maintain hazy skies and keep
surface visibilities periodically reduced near 6 statute miles
through the end of the short-term period.

&&

.Long Term(Thursday through next Sunday)...
Issued at 210 AM AST Mon Aug 10 2026

A tightening pressure gradient associated with the Atlantic ridge
will support breezy easterly to southeasterly winds Thursday into
the weekend. A drier air mass and Saharan dust will dominate, with
precipitable water values dropping to around 1.3 inches Thursday
and only brief patches of low-level moisture thereafter. Shower
activity should remain limited, with mainly passing showers and
very localized afternoon convection. Fewer clouds, warm low-level
temperatures, and sufficient low-level humidity will maintain an
elevated to significant heat risk, especially across coastal and
urban areas, where heat indices could approach 114 degrees.
Strengthening trades will also lead to deteriorating marine and
coastal conditions late in the week, with building seas and an
increasing rip current risk.

Forecast confidence decreases late in the period as NHC continues
to monitor multiple disturbances across the central and eastern
tropical Atlantic. Guidance suggests that one of these systems
could approach the northeastern Caribbean early next week, but
considerable uncertainty remains regarding its track, strength,
timing, and any potential local impacts. Therefore, the forecast
for Monday and beyond may change depending on how these systems
evolve.

&&

.AVIATION...
(18Z TAFS)
Issued at 150 PM AST Mon Aug 10 2026

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. Mostly VCSH expected across all
terminals through 10/22z due to shallow/locally induced -SHRA.
The 10/12z TJSJ sounding indicated east winds up to 30 kt blo
FL100. HZ due to Saharan dust will continue through the period,
and VSBY may drop to 6SM.

&&

.MARINE...
Issued at 150 PM AST Mon Aug 10 2026

The broad Atlantic ridge extending from the western into the central
Atlantic will continue to promote moderate to locally fresh easterly
winds tonight, becoming moderate on Tuesday as the local pressure
gradient slightly weakens. A tropical wave crossing the eastern
Caribbean Tuesday into Wednesday will increase the potential for
showers and thunderstorms over the local waters. Followed by the
tropical wave, winds will begin increasing again Wednesday night as
the pressure gradient tightens, becoming fresh to locally strong by
Thursday night into Friday. Choppy to rough seas across the regional
waters and local passages are likely, leading to hazardous
conditions for small craft.

&&

.BEACH FORECAST...
Issued at 150 PM AST Mon Aug 10 2026

The beach forecast remains on track. The latest nearshore buys
reported seas between 2 and 3 feet, leading to breaking waves up to
4 feet. Hence, the moderate risk of rip currents continues across
northern and eastern beaches of Puerto Rico, including Vieques and
Culebra, and the U.S. Virgin Islands. When visiting a beach under a
moderate risk, beachgoers should pay attention to the beach
conditions as life-threatening rip currents remain possible along
the surf zone. Although winds may weaken on Tuesday, the moderate
risk should continue for the next few days. Model guidance
suggests strengthening winds, which could potentially increase
breaking waves and lead to a high risk of rip currents this
weekend. Residents and visitors should stay up to date with the
latest issuance of the beach forecast.

Besides rip currents, beachgoers should stay weather alert,
particularly on Tuesday and Wed, as the approach of a tropical wave
will likely increase the likelihood of showers and isolated
thunderstorms moving near coastal areas of the islands. Periods of
heavy rainfall, gusty winds, and lightning could become hazardous,
beachgoers should seek shelter whenever they hear thunder.

&&

.FIRE WEATHER...
Issued at 150 PM AST Mon Aug 10 2026

The islands continue with critical fuels as moderate to extreme
drought levels persist. The latest satellite-derived products show
lingering moisture associated with a tropical wave across the CWA,
with a drier airmass in the low to mid levels filtering into the
region. Nevertheless, RH values dropped during the morning hours,
particularly across the southern coastal plains of Puerto Rico,
below thresholds (< 55%).  Additionally, breezy to locally windy
conditions continue across the islands, as RAWs stations reported
winds between 15 - 25 mph and gusts up to 35 mph. Taking into
consideration the dry fuels and KDBIs well above thresholds, the
fire danger threat should remain elevated today; the Fire Danger
Statement continues in effect through 5 PM AST. Residents and
visitors are encouraged to avoid outdoor burning, as conditions will
likely be favorable for wildfire ignition and rapid spread.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>005-007-
     008-010>013.

VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

AVIATION/SHORT TERM...DSR
KEY/BEACH/MARINE/FIRE....MNG
LONG...LIS/MRR