414
FXCA62 TJSJ 111844
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
244 PM AST Fri Jul 11 2025

.KEY MESSAGES...

* A dense Saharan Air Layer will persist through at least early Sunday,
  maintaining hazy skies, reduced visibility, and unhealthy air
  quality levels across Puerto Rico and the US Virgin Islands.

* Limited overnight cooling due to the Saharan dust will lead to
  warmer- than-normal mornings and dangerously hot daytime
  temperatures, especially in coastal and urban areas. Heat
  advisories remain likely.

* Moderate to fresh winds will prevail, with isolated trade wind
  showers mainly across eastern areas at night and early morning.
  Afternoon shower activity will shift farther south due to
  changing wind patterns.

* A tropical wave will arrive for the middle of next week.

* 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 Sunday...

Mostly sunny and hazy skies persisted across Puerto Rico and the
US Virgin Islands due to a dense Saharan Air Layer (SAL) with
moderate to high concentrations of suspended dust particles. Warm
to hot heat indices were recorded around the coastal locations,
where a Heat Advisory was still in effect. Winds were from the
east-southeast at 10 to 20 mph with higher wind gusts and sea
breeze variations.

A few afternoon showers will develop across the western
locations, while the rest of the region will observe mainly hazy
skies and uncomfortable heat indices the rest of the afternoon.
This evening, isolated trade wind showers may drift across the
islands, producing light rainfall mainly over eastern Puerto Rico
and the USVI. Minimum temperatures will remain warm, staying in
the low 80s across coastal and lower elevations, and ranging from
the mid-60s to low 70s in the interior highlands. Winds will shift
from east-northeast to northeast between 612 mph, with
occasional gusts up to 20 mph.

A high-pressure system extending from the surface to the low-mid
levels will maintain breezy conditions today and Saturday, with
east to east-southeast winds around 1520 mph. By Saturday night
into Sunday, the weakening of this high and the influence of a new
high from the central Atlantic will shift winds more
northeasterly. This change will result in afternoon showers
focusing farther south than in previous days, and slightly lower
heat indicesespecially by Sunday.

Despite these subtle changes, expect hazy and hot conditions to
continue through the weekend, with limited overnight cooling due
to the SAL. As a result, mornings will start warmer than usual,
and daytime highs across coastal and urban areas will remain above
normal. Heat advisory conditions are likely to persist. Residents
and visitors should stay hydrated, avoid prolonged sun exposure,
and limit outdoor activityparticularly those sensitive to heat
and poor air quality.

A surface high pressure across the central Atlantic will continue
to result in moderate southeasterly winds across the region.
Therefore, 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 hazy skies,
reduced visibilities a deteriorated air quality.

.LONG TERM...Monday through Friday...from previous discussion...

A enhancement in moisture levels is expected by the beginning of
the workweek with the arrival of several trade wind perturbations
into the islands. The latest precipitable water content shows
values between 1.60 to 2.00 inches from early Monday through late
Tuesday. Therefore, there is an increase in the potential for
shower activity across the area, in particular over eastern Puerto
Rico and the U.S. Virgin Islands during the morning hours.

As the week progresses, a tropical wave is expected to approach the
islands from the east by early evening on Wednesday and lasting
through at least Friday. The latest model guidances has the bulk of
the wave arriving into the area by Thursday morning, increasing the
chance for showers and thunderstorms across the region with PWAT
values up to 2.20 inches. Despite of the wave passage, moderate to
heavy showers and thunderstorms are anticipated each afternoon,
particularly across the central and western municipalities of Puerto
Rico. We will continue to monitor the weather conditions closely for
any significant changes in the forecast.

Saharan dust concentrations will begin to decrease on Monday.
Nonetheless, minor concetrations of these particles will continue to
linger across the region through Thursday. Another pulse of
Saharan dust will arrive by late Thursday/ early Friday following
the wave passage. This event will promote, once again, hazy skies,
reduced visibilities and deteriorated air quality throughout the
area until the weekend.

&&

.AVIATION...
(18Z TAFs)

Mainly VFR conditions are expected to prevail across all TAF sites
during the forecast period. Some passing VCSH cannot be ruled out
across TJBQ through around 11/22Z. Main aviation concerns remain to
be the Saharan Air Layer resulting in reduced visibilities and the E-
ESE breezy winds through around 11/23Z. Then , lighter winds are
expected overnight, increasing again Saturday morning (after 12z-
13Z) to around 14 to 18 knots with gusts up to 25 to 28 knots.

&&

.MARINE...

A surface high pressure across the central Atlantic will continue
to result in moderate southeasterly winds across the region.
Therefore, 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 hazy skies,
reduced visibilities a deteriorated air quality.

&&

.BEACH FORECAST...

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

Precautions:
Swim only near lifeguards, heed posted warnings. Conditions may quickly
become dangerous, especially for less experienced swimmers.

Hot, hazy conditions are expected to persist through the weekend with
heat index values likely exceeding the 108F in urban and coastal
zones.

Safety Tips:
Stay well hydrated. Seek shade frequently. Avoid outdoor activity
during peak sun hours (typically 11AM2PM).

&&

.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