440
FXCA62 TJSJ 101749
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
149 PM AST Thu Jul 10 2025

.KEY MESSAGES...

* Hazy skies and poor air quality due to Saharan dust will
  persist through the weekend, especially impacting sensitive
  groups.

* Warmer-than-normal nights and hot daytime temperatures will
  continue, with heat indices reaching levels that may warrant
  Heat Advisories or Extreme Heat Warningsparticularly in urban
  and coastal areas.

* A moderate risk of rip currents continues along north- and east-
  facing beaches of Puerto Rico and parts of the U.S. Virgin
  Islands.

&&

.SHORT TERM...Tonight through Saturday...

After the surge of moisture that brought scattered to widespread
showers across the islands, a slot of dry air limits rain activity
and produces hazy skies. Maximum temperatures were in the low and
mid-90s along the urban coastal areas, with warm to hot maximum
heat indices. At the same time, the mountain zones observed
maximum temperatures between the mid-80s and low 80s degrees
Fahrenheit. Winds were from the east to east northeast at 15 to
25 mph, with higher gusts and variations due to sea breezes.

Following the passage of todays perturbation, stronger east-
southeasterly winds will promote breezy conditions and usher in a
much drier air mass, with precipitable water values expected to
fall between 1.15 and 1.35 inches. This drier environment will
coincide with moderate to high concentrations of Saharan dust,
signaling the onset of a hazy, warmer, and more stable weather
pattern across Puerto Rico and the US Virgin Islands, expected to
prevail through the weekend. At the mid-to-upper levels, a trough
located to the northeast of the region will gradually replace the
retreating mid-level ridge, settling northwest of the islands by
Saturday. However, the extensive mid-level dry air mass will
minimize the impacts of this trough aloft by promoting subsidence
aloft in the area.

Tonight marks a transitional period, with residual afternoon and
evening convection across western Puerto Rico giving way to
increasingly dry and hazy conditions that will suppress additional
shower development. As a result, visibility and air quality will
deteriorate, especially for sensitive populations. Fair and dry
weather will dominate across the US Virgin Islands and eastern
Puerto Rico. Regardless of these conditions, we cannot rule out
the possibility of a pocket of moisture arriving, resulting in a
few passing showers across the windward locations. Then, diurnal
heating and local effects may produce reduced afternoon convection
each day.

Warmer-than-normal minimum temperatures are expected to return
due to this concentration of SAL, which will reduce nighttime
cooling. As days begin warmer than normal, maximum temperatures
will reach above normal levels, which, combined with the available
low-level moisture, will result in warm to hot heat indices.
These heat indices may reach levels that prompt Heat Advisories or
Extreme Heat Warnings, particularly in urban and lower-elevation
areas of Puerto Rico.

Residents and visitors, as well as the sensitive communities, are
advised to take appropriate precautions during this period,
particularly those who are sensitive to reduced air quality and
heat.

.LONG TERM...Sunday through Thursday...from prev discussion...

On Sunday, Saharan Dust concentrations will begin to diminish.
However, we still anticipate hazy skies across the U.S. Virgin
Islands and Puerto Rico. The latest model guidance continues to
indicate a Tropical Upper-Tropospheric Trough (TUTT) shifting
westward towards Hispanola and lingering there through the
beginning of the workweek weakening the high pressure system at
the surface and forcing the breezy to locally windy conditions to
diminish.

On Monday and Tuesday, 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, particularly during the
afternoon hours over western and southwestern Puerto Rico, with
pockets of showers over eastern Puerto Rico in the morning hours.
Additionally, model guidance indicate that moisture will extend
from the surface through the mid and upper levels of the
atmosphere, supporting increased atmospheric instability and
enhancing the potential for convective development during this
period.

By midweek, a tropical wave is expected to approach the forecast
area, bringing increased 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...

SHRA will likely form near or over TJBQ btwn thru 10/23Z,
possibly causing brief MVFR conds. VCSH are also possible around
TJSJ and USVI terminals throughout the period, especially after
10/23Z. We expect hazy skies with visibilities reduced between
5-6SM due to the arrival of moderate to high concentrations of
suspended Saharan dust particles. Breezy to locally windy winds of
16-22 kt thru 10-23Z, diminishing to 10-15 kt aft 10/23Z, but
returning to similar speeds tomorrow aft 11/13z.

&&

.MARINE...

Mariners can expect moderate to fresh easterly winds and choppy
seas across the islands through the weekend. An extensive Saharan
Air Layer will move across the Northeastern Caribbean lingering
through the weekend, and leaving a tropical wave well south of the
islands.

&&

.BEACH FORECAST...

Moderate to high rip current risk continues along north- and east-
facing beaches of Puerto Rico and parts of the USVI. Always swim
near lifeguards and obey posted warnings. Conditions may be
dangerous for inexperienced swimmers.

Expect hot and hazy conditions through the weekend, with
excessive heat posing a riskespecially in urban and coastal
areas. Heat indices may exceed 108F, so stay hydrated, seek
shade, and avoid peak sun hours.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010-011.

VI...None.
AM...None.
&&

$$

SHORT TERM...CAM
LONG TERM....YZR
AVIATION...YZR