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619
FXCA62 TJSJ 121915
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
315 PM AST Sun Jul 12 2026

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

.KEY MESSAGES...
Issued at 312 PM AST Sun Jul 12 2026

* Lingering moisture associated with the tropical wave will continue
  to support isolated to scattered afternoon showers across portions
  of western and interior Puerto Rico on Monday.

* A Heat Advisory may again be required on Monday as lingering
  tropical moisture combined with hot temperatures could result in
  heat indices reaching advisory criteria across portions of the
  coastal and urban areas.

* Moderate concentrations of Saharan dust will persist today, with a
  higher concentration expected to overspread the islands late
  tonight into Monday. Hazy skies and reduced visibility will
  continue at times.

* Breezy easterly winds will persist through much of the week. While
  winds are expected to be slightly weaker than last week, they will
  continue to produce choppy marine conditions and hazardous
  conditions for small craft at times.

* A moderate risk of rip currents continues across several local
  beaches. Life-threatening rip currents remain possible,
  especially near piers, jetties, and sandbars.

&&

.Short Term(This evening through Tuesday)...
Issued at 312 PM AST Sun Jul 12 2026

Fair weather conditions have prevailed across the region through the
morning hours under the influence of a drier-than-normal and stable
air mass. The 12Z TJSJ sounding measured 1.49 inches of precipitable
water (PWAT), which is in the 25th percentile for this time of year.
GOES satellite imagery also suggested similar values this morning.
Surface observations have registered sustained winds of 14 to 18
mph, with frequent gusts up to 30 mph across the islands. Low to
moderate concentrations of Saharan dust have also resulted in hazy
skies. Afternoon temperatures across urban and lower-elevation areas
have climbed into the upper 80s and low 90s, producing heat indices
generally in the upper 90s to low 100s, with some urban locations,
particularly across northern and western Puerto Rico, exceeding
105F. A Heat Advisory remains in effect through 5 PM AST.

For the rest of the afternoon, a broad surface high-pressure system
over the central Atlantic and a persistent mid-level ridge extending
westward across the northeastern Caribbean will maintain moderate to
locally fresh easterly winds. Additionally, a weak tropical wave is
passing south of the area between today and tomorrow. This will
increase precipitable water (PWAT) values to around 1.75 inches,
which is considered seasonal. Although widespread rainfall is not
expected, the combination of daytime heating, local sea-breeze
convergence, modest instability aloft, and increasing low-level
moisture will be sufficient to support scattered afternoon
convection across the western interior and western sections of
Puerto Rico today and again on Monday afternoon. As a result, the
best chance for rainfall during the short term period will occur
this afternoon and Monday afternoon across western Puerto Rico.

Additionally, the presence of Saharan dust will continue, with
concentrations increasing from low to moderate today to high levels
beginning late tonight and continuing into Monday and Tuesday. This
will result in hazy skies, reduced visibility, and deteriorating air
quality. Individuals in sensitive groups, including those with
respiratory conditions, young children, and older adults, should
take appropriate precautions and limit prolonged outdoor exposure
during this period.

On Tuesday, moisture levels will decrease again to around the 25th
percentile as the peripheral moisture associated with the passing
tropical wave exits the area and strong stability returns under the
influence of the upper-level ridge. With the presence of Saharan
dust, above normal 925 temperatures, available moisture, and
localized afternoon rainfall, the heat risk will likely remain
elevated, prompting additional Heat Advisories during the short-term
forecast period. Stay tuned to the forecast for the latest
updates.

&&

.Long Term(Wednesday through next Saturday)...
Issued at 340 AM AST Sun Jul 12 2026

From Wednesday through Saturday, the primary impacts will
be periods of hazy skies, reduced visibility, poor air quality, and
hot daytime conditions as a Saharan Air Layer (SAL) affects the
region. Moderate to locally high concentrations of Saharan dust are
expected Wednesday through Thursday, resulting in the greatest
impacts during this long term period, particularly for sensitive
individuals in areas of thicker dust concentrations. Dust
concentrations should gradually decrease toward the weekend,
although some haze may linger through Saturday.

Shower activity will generally remain limited throughout the period.
On Wednesday, passing trade-wind showers will favor the U.S. Virgin
Islands and eastern Puerto Rico during the morning, followed by
isolated to scattered afternoon showers across the interior and
western sections of Puerto Rico. An increase in low and mid-level
moisture on Thursday may result in slightly greater shower coverage.
However, warm mid-level temperatures, modest lapse rates, and the
lingering influence of the SAL will maintain a relatively stable
atmosphere, preventing widespread deep convection. By Friday and
Saturday, moisture decreases to near or below normals while stable
mid-level conditions persist, limiting rainfall mainly to brief
trade-wind showers and isolated afternoon convection over western
Puerto Rico. No flooding concerns are anticipated through the period.

Seasonal to slightly above-normal temperatures are expected
throughout the period. Combined with abundant sunshine and
sufficient low-level moisture, afternoon heat indices will likely
exceed 100 degrees Fahrenheit across urban and coastal areas,
particularly along the northern and southern coastal plains of
Puerto Rico and portions of the U.S. Virgin Islands. The presence of
Saharan dust through Thursday may also limit overnight radiational
cooling, resulting in warmer-than-normal minimum temperatures and
prolonging heat stress despite the gradual drying trend.

&&

.AVIATION...
(18Z TAFS)
Issued at 312 PM AST Sun Jul 12 2026

VFR conds will prevail across all terminals through the fcst period.
VCSH/SHRA are more probable across the vicinity of TJBQ during the
afternoons. Main aviation concerns are the haze and winds. HZ will
increase further from late tonight into Monday over the local
islands, reducing vis. Gusty conds will prevail, with E-ESE sfc
winds at around 15 kt with gusts up to 30 kt will continue through
around 12/23Z, becoming lighter overnight. By 13/14Z, winds are
expected to pick up again.

&&

.MARINE...
Issued at 312 PM AST Sun Jul 12 2026

A weak tropical wave continues moving south of the local islands
across the Caribbean Sea. Meanwhile, strong Atlantic high pressure
will maintain moderate to locally fresh easterly to east-
northeasterly winds, resulting in choppy seas across the regional
waters. A pulse of Saharan dust will continue spreading across the
local waters through the remainder of the afternoon and tonight,
leading to hazy conditions and occasional reductions in visibility.
The Atlantic high will continue to maintain a tight local pressure
gradient through early this week, sustaining moderate to fresh east
to east-southeast winds and hazardous marine conditions.

&&

.BEACH FORECAST...
Issued at 312 PM AST Sun Jul 12 2026

Breezy trade winds will continue to generate choppy seas across the
local waters through at least early this week, resulting in a
moderate risk of life-threatening rip currents across many beaches
of Puerto Rico and the U.S. Virgin Islands. The risk will remain
elevated, particularly along north-, east-, and southeast-facing
beaches. Beachgoers should swim near lifeguards whenever possible,
heed beach warning flags, and never swim alone.

Hot and humid conditions will continue through Monday, with heat
indices expected to reach advisory levels across portions of the
coastal and urban areas. Stay well hydrated, seek shade whenever
possible, and apply sunscreen to help reduce the risk of heat-
related illnesses.

A new pulse of Saharan dust will continue spreading across the
islands late tonight into Monday, resulting in hazy skies and
occasional reductions in visibility.

&&

.FIRE WEATHER...
Issued at 312 PM AST Sun Jul 12 2026

Surface stations across southern Puerto Rico have been registering
relative humidity (RH) values in the 40s and 50s, along with wind
gusts in the upper 20s to low 30s mph today. Therefore, a Fire
Danger Statement remains in effect until 5 PM AST, highlighting an
elevated fire danger risk. Moisture is expected to gradually
increase through the afternoon due to peripheral moisture associated
with a tropical wave moving well south of the Caribbean, providing
some relief to the low RH values. However, despite this slight
increase in moisture, ongoing dry conditions and critically dry
fuels resulting from persistent rainfall deficits will continue to
favor rapid fire growth and spread across much of Puerto Rico,
Vieques, Culebra, and St. Croix. Fire weather partners are advised
to remain vigilant.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM/AVIATION/FIRE...YZR
LONG TERM...MMC
MARINE/BEACH...CVB

NWS SJU Office Area Forecast Discussion