615
FXCA62 TJSJ 091857
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
257 PM AST Wed Jul 9 2025

.KEY MESSAGES...

* Passing showers will continue across the USVI and eastern
  sections of PR tonight into Thursday morning hours. Diurnally
  induced afternoon showers and isolated thunderstorms are
  expected over portions of the Cordillera Central and western PR
  each day.

* Breezy to locally windy conditions will promote choppy seas and
  a moderate risk of rip currents over the next few days.

* Moderate to high concentrations of Saharan dust are expected to
  return late tonight through at least Sunday, resulting in hazy
  skies, reduced visibility, and poor air quality.

&&

.SHORT TERM...Tonight through Friday...

A wind surge will promote rough seas due to moderate to locally
fresh winds across the local waters, accompanied by scattered to
numerous showers through at least Thursday morning. Another easterly
perturbation will reach the Lesser Antilles late tonight, moving
near the US Virgin Islands and Puerto Rico by late Thursday night
and early Friday morning. Another pulse of suspended Saharan dust
particles will arrive as early as late tonight and persist through
the weekend.

Overnight, scattered to numerous showers moved across the local
waters, with some reaching windward areas of the U.S. Virgin Islands
and Puerto Rico. This activity was associated with a wind surge that
increased local winds and generated rough seas for mariners. Skies
were variably cloudy, with temperatures ranging from the low to mid-
60s in the mountains and valleys to the upper 70s and low 80s in
urban coastal areas.

A wind surge will bring scattered showers and stronger winds across
the region starting today. From Thursday to early Friday morning, a
tropical wave accompanied by a band of moisture with precipitable
water values ranging from 1.85 to 2.10 inches will move through the
area. However, higher concentrations of Saharan dust embedded within
the wave may limit overall shower development. As a result, a
similar weather pattern is expected each day, with passing showers
across the U.S. Virgin Islands and eastern Puerto Rico during the
night and early morning, followed by afternoon convection over
central and western Puerto Rico and streamer development downwind of
the USVI and El Yunque. Localized impacts may include ponding of
water on roads, poorly drained areas, as well as urban and small
stream flooding, particularly during heavier thunderstorms. Moisture
will rapidly erode after Friday morning.

Additionally, based on the latest model guidance, an area of
suspended Saharan dust particles is forecast to move across Puerto
Rico and the U.S. Virgin Islands as early as tonight, continuing
through the weekend. This will result in hazy skies, reduced
visibility, and deteriorated air quality across the region.
Sensitive groups should take precautionary measures, as airborne
particulates may impact respiratory health.

Recent observations suggested the arrival of a pocket of dry air
across the southern slopes resulting in RH drops around the low and
mid 50s with sustained winds between 15 mph and higher gusts.

.LONG TERM...Saturday through Wednesday...
.PREV DISCUSSION... /issued 452 AM AST Wed Jul 9 2025/

The latest model guidance continues to indicate the arrival of
Saharan Dust particles along with a notably dry airmass through at
least late Sunday. Additionally, mid to upper level dry air and a
reinforcing trade wind inversion will further inhibit vertical
cloud development, suppressing widespread convection. With this
setup, residents and visitors in Puerto Rico and the U.S. Virgin
Islands can expect hazy skies, reduced visibility, and potential
air quality concerns, particularly for individuals with
respiratory conditions. Breezy conditions will prevail through
Saturday, with persistent easterly winds supporting above-normal
temperatures, especially across coastal and urban areas.

By Sunday, a Tropical Upper-Tropospheric Trough (TUTT) is forecast
to shift westward toward Hispaniola and linger there through
midweek. Beginning Monday, the approach of easterly trade wind
perturbations will gradually enhance moisture levels across the
region. As atmospheric moisture increases, so will the potential
for shower and thunderstorm activity.

Tuesday currently appears to have the highest rainfall potential as
a tropical wave approaches the forecast area, bringing deeper
tropical moisture. However, the most intense part of the wave is
expected to pass south of Puerto Rico and the U.S. Virgin Islands.
Nevertheless, scattered showers and thunderstorms are anticipated
each afternoon, especially across interior and western areas. We
will continue to monitor conditions closely for any significant
changes.

&&

.AVIATION...
(18Z TAFs)

Mainly VFR conds are expected to prevail across all terminals.
However, expect diurnally induced afternoon SHRA over the interior
and W-PR and downwind from el Yunque, with most of the activity in
the VCTY of our terminals. Some SHRA/-SHRA will form near the USVI
and E-PR terminals, btwn 10/02-12z. Higher concentrations of Saharan
dust return from Thursday onward and visibilities could drop to 5-6
SM. Winds will continue E-ENE at 15-25 kt with higher gusts and sea
breeze variations, winds will return around 10 kt aft 09/23z.

&&

.MARINE...

A surface high pressure across the Atlantic with promote moderate
to fresh easterly winds resulting in Small Craft Advisories across
the offshore and onshore Atlantic waters and the Anegada passage
through at least Thursday morning and choppy seas across most local
waters over the next few days. An easterly perturbation will reach
the area tonight, increasing the frequency of showers across the
waters. Additionally, another pulse of suspended Saharan dust
particles will arrive late tonight and persist through next Sunday
resulting in hazy skies and reduced visibility.

&&

.BEACH FORECAST...

Breezy to locally windy conditions over the next several days
will promote a persistent moderate risk of rip currents across
most local beaches of Puerto Rico and the US Virgin Islands.
Beachgoers are encouraged to exercise caution as life-threatening
rip currents are possible in the surf zone.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory until noon AST Thursday for AMZ711.

     Small Craft Advisory until midnight AST tonight for AMZ712.

     Small Craft Advisory until 6 AM AST Thursday for AMZ723.

&&

$$

SHORT TERM/AVIATION...CAM
LONG TERM...MMC
PUBLIC...YZR