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467
FXCA62 TJSJ 190648
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
248 AM AST Fri Jun 19 2026

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

.KEY MESSAGES...
Issued at 247 AM AST Fri Jun 19 2026

* A Heat Advisory is in effect today for the coastal and urban
  locations in PR and the USVI. This level of heat affects most
  individuals sensitive to heat, especially those without
  effective cooling and/or adequate hydration.

* Dangerous heat index values will continue each afternoon as hot
  temperatures mix with moisture, raising the risk of heat
  exhaustion and heat stroke, particularly in coastal and urban
  areas, poorly ventilated locations, and among vulnerable groups.

* Moderate to high concentrations of Saharan dust will spread
  across Puerto Rico and the U.S. Virgin Islands through at least
  late Saturday night, and possibly into early Sunday morning,
  reducing air quality and visibility while potentially
  aggravating respiratory conditions among sensitive groups.

* A tropical wave will pass through the region on Sunday, raising
  the likelihood of heavy rainfall, thunderstorms, and urban and
  small-stream flooding, as well as the potential for isolated
  flash flooding across parts of Puerto Rico and the U.S. Virgin
  Islands.

* Life-threatening rip currents will persist at exposed beaches
  in Puerto Rico and the U.S. Virgin Islands for the duration of
  the forecast. Beach visitors should exercise caution and adhere
  to local beach safety guidance.

&&

.Short Term(Today through Sunday)...
Issued at 247 AM AST Fri Jun 19 2026

Overnight, we had little or no rain as a drier air mass with
moderate to high concentrations of Saharan Air Layer (SAL) began
to filter over the Northeast Caribbean. The Saharan Air Layer
(SAL) limited nocturnal radiational cooling through the absorption
and re-emission of outgoing longwave radiation by mineral dust
particles. As a result, overnight temperatures remained near or
above climatological normals, with minimum temperatures generally
ranging from the upper 70s to the lower 80s across coastal and
urban areas. Although most wind stations reported east to east-
southeast winds of 5 to 15 mph with land-breeze fluctuations, some
stations in Culebra and the Northern US Virgin Islands observed
northeast winds of 15 to 20 mph with higher gusts.

Today, residents and visitors of the US Virgin Islands and Puerto
Rico can expect hazy skies as a SAL continues to filter over the
islands with moderate to high concentrations of suspended dust
particles. This air mass will degrade air quality and visibility,
potentially aggravating respiratory conditions among sensitive
groups. Additionally, the warmer-than-normal start to the day will
promote warm and hot temperatures (which model guidance suggests
are in the 75th percentile for June climatology), combined with
available moisture, resulting in dangerous heat index values,
especially between 10 and 4 PM AST. This level of heat affects
most individuals sensitive to heat, especially those without
effective cooling and/or adequate hydration. Thus, a Heat Advisory
is in effect for the coastal and urban locations in the USVI and
PR.

Regardless of the weather pattern described above, a strong
surface high pressure across the Atlantic Ocean will tighten the
local pressure gradient, promoting east-southeast winds that will
transport occasional pockets of moisture, clouds, and showers
into the region today and Saturday. Under this weather pattern,
expect warm to hot temperatures, breezy conditions, and occasional
passing showers across the USVI and PR`s windward sectors. At the
same time, daytime heating and local effects may trigger isolated
to scattered afternoon convection across the interior and western
portions of Puerto Rico.

Although NASA Dust Aerosol Optical Thickness guidance continues to
indicate low to moderate concentrations of Saharan dust across the
region on Sunday, a tropical wave is forecast to approach and move
through the islands by Sunday afternoon (Father`s Day). This
feature will increase moisture availability and enhance the
potential for showers and thunderstorms, raising the risk of heavy
rainfall, urban and small-stream flooding, and isolated flash
flooding across portions of Puerto Rico and the U.S. Virgin
Islands. As a result, the greatest likelihood for widespread
rainfall and thunderstorm activity is expected on Father`s Day.
However, forecast confidence regarding the extent and intensity of
rainfall remains somewhat uncertain, as it depends on the balance
between the moist air mass associated with the tropical wave and
the drier, more stable air mass accompanying the Saharan Air Layer
(SAL). We will continue to closely monitor evolving conditions and
refine the forecast as confidence increases.

&&

.Long Term(Monday through Friday)...
Issued at 247 AM AST Fri Jun 19 2026

Model guidance continues to indicate a gradual improvement in
weather conditions by Monday and persisting through midweek as a
drier air mass filters into the region. Precipitable water values
are forecast to decrease from near normal values (1.8 inches) on
Monday to below-normal levels by Tuesday and Wednesday. Surface and
mid-level relative humidity values are also expected to trend
downward, resulting in a more stable atmospheric profile. With these
stable conditions, we anticipate warm weather with temperatures
along the coastal areas in the upper 80s to low 90s and in the 70s
to low 80s across the higher terrains and rural areas. Residents and
visitors should continue to practice heat safety, including staying
hydrated and limiting prolonged outdoor activities during the
hottest part of the afternoon, particularly across coastal and urban
areas where heat indices may approach uncomfortable levels.

Although some passing trade-wind showers will remain possible across
windward areas through the period, overall shower coverage and
intensity should gradually diminish from Monday into Wednesday.
While brief periods of wet roads may occur, especially across
windward locations, significant rainfall impacts are not expected.
As moisture decreases and atmospheric stability improves, a return
to a more typical trade-wind weather pattern is anticipated through
midweek, supporting generally favorable conditions for outdoor
activities.

By Thursday, model guidance suggests a gradual increase in moisture
across the area, leading to an uptick in shower activity. However,
widespread rainfall is not currently anticipated, and conditions
should remain generally favorable. Nevertheless, the increase in
moisture may result in more frequent showers capable of producing
localized ponding of water on roadways and minor flooding in poor-
drainage and low-lying areas. Residents should monitor the latest
forecasts and remain alert for changing weather conditions,
especially if living in or traveling through flood-prone locations.

&&

.AVIATION...
(06Z TAFS)
Issued at 247 AM AST Fri Jun 19 2026

A dense Saharan Air Layer will lower visibilities across local
terminals today and early Saturday. Thus, expect HZ and VSBY could
drop to near 6 SM. This air mass will limit the potential for
SHRA/TSRA; however, occasional SHRA/-SHRA will be advected across
local terminals by the E-ESE winds at 10-20 kt, with higher gusts
between 20 and 30 kt. This may impact JSJ/IST or ISX. JBQ will
observe limited afternoon SHRA between 19/15-22z.

&&

.MARINE...
Issued at 247 AM AST Fri Jun 19 2026

A broad surface high pressure building over the Central Atlantic
will continue to promote moderate to locally fresh east to east-
southeast winds over the next several days, resulting in choppy seas
across local waters and Caribbean passages; small craft should
exercise caution. A dense layer of Saharan Dust will continue to
filter into the region through the weekend, resulting in hazy skies,
reduced visibility, and poor air quality through Fathers Day
weekend. A tropical wave is expected to move across the Caribbean
Sea Sunday into Monday.

&&

.BEACH FORECAST...
Issued at 247 AM AST Fri Jun 19 2026

Breezy to locally windy conditions will maintain a low to moderate
risk of rip currents during the next few days. Areas under a
moderate risk of rip currents (life-threatening rip currents are
possible in the surf zone) today and tonight include, southeastern,
north-central and northwestern PR, Culebra and St. Croix. The
moderate risk is forecast to spread across most of the local
beaches as winds strengthen, with most beaches being under a
moderate risk late in the weekend into the workweek.

A low risk of rip currents will also persist for most of the rest
of the local beaches today and tonight. However, life-threatening
rip currents often occur in the vicinity of groins, jetties,
reefs, and piers.

Concentrations of Saharan Dust will continue to move over the
islands throughout the period, resulting in hazy skies, reduced
visibility, and poor air quality. High heat indices will also
persist during the forecast period, sensitive groups should take
necessary precautions.

&&

.FIRE WEATHER...
Issued at 247 AM AST Fri Jun 19 2026

A RED FLAG WARNING has been issued for today across portions of
southern and western Puerto Rico, Vieques and St Croix, where the
greatest fire danger is expected from late morning through the
afternoon. Expect breezy east to east-southeast winds and windy
gusts, as well as dangerous low RH values, creating high risk of
fire weather conditions. These conditions combined with
critically dry fuels will promote the rapid spreading of any fire
that develops.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 9 AM this morning to 6 PM AST this evening
     for PRZ001>005-007-008-010>013.

     Red Flag Warning from 10 AM this morning to 4 PM AST this
     afternoon for PRZ014-015-018-025-027.

VI...Heat Advisory from 9 AM this morning to 6 PM AST this evening
     for VIZ001-002.

     Red Flag Warning from 10 AM this morning to 4 PM AST this
     afternoon for VIZ002.

AM...None.

&&

$$

KEY MESSAGES/SHORT TERM/AVIATION/FIRE WEATHER...CAM
LONG TERM....MMC
MARINE/BEACH FORECAST...MRR

NWS SJU Office Area Forecast Discussion