016
FXCA62 TJSJ 200726
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
326 AM AST Wed Aug 20 2025

.KEY MESSAGES...

* Another very hot day for Puerto Rico and the Virgin Islands.
  Heat indices above 108 degrees are expected across most of the
  territories.

* Saharan dust will increase in concentration today, first
  reaching the Virgin Islands, and then spreading into Puerto
  Rico. These concentrations will maintain hazy skies through
  Thursday.

* Marine conditions will deteriorate by the end of the week as a
  northerly swell arrives. Beaches will be hazardous along the
  northern and western coast of Puerto Rico, as well as for St.
  Thomas and St. John.

&&

.SHORT TERM...Today through Friday...

Calm and quiet weather conditions prevailed overnight across Puerto
Rico and the U.S. Virgin Islands. Doppler radar observed just few
passing showers moving from the Caribbean waters into portions of
southern Puerto Rico, leaving minimal accumulations. Minimum
temperatures were seen in the range from the upper 70s to low 80s in
the lower elevations, to the low 70s in the mountains. These warm
minimum temperatures are expected to persist for the next few days
under a southeasterly wind flow.

A Saharan Air Layer (SAL) with moderate to locally high
concentrations of Saharan dust will continue to filter into the area
through at least early Thursday morning. The peak of the event is
expected a by this afternoon into the evening hours. Therefore, hazy
skies, reduced visibilities and deteriorated air quality are
anticipated throughout the day across the islands. Under the
aforementioned pattern, the shower activity will remain limited
across the islands. Nonetheless, afternoon convective activity is
still possible each day over portions of central and northwestern
Puerto Rico due to southeasterly winds, daytime heating and local
effects.

Hot temperatures will continue across Puerto Rico and the U.S.
Virgin Islands. The combination of southeasterly winds and
sufficient moisture will result in high temperatures and high heat
indices through next week. Once again, a Extreme Heat Warning has
been issued from 9 AM to 5 PM AST for the eastern interior and the
lower elevations of Puerto Rico. A Heat Advisory is also in effect
for Culebra, Vieques and the U.S. Virgin Islands from 9 AM to 5 PM
AST. Residents and visitors should plan accordingly if planning to
do outdoor activities under sun exposure for a prolonged time.

.LONG TERM...Saturday through Wednesday...

The latest guidance continue to suggest that the strong tropical
wave monitored by the National Hurricane Center should move to the
northeast of the local islands on Saturday. This wave will shift
the winds from the north, which plenty of moisture reaching Puerto
Rico and the Virgin Islands. Showers and thunderstorms are
expected to stream into the region, maintaining and elevated risk
of flooding, and a limited risk of lightning. As the wave lifts
into the western Atlantic, the trade winds will turn southeast as
the air mass dries. Some Saharan dust will reach the island by
early in the workweek. Temperatures will warm up too, with a high
likelihood of experiencing heat that impacts those sensible to
heat, especially without effective cooling or adequate hydration.

By Tuesday, and upper level trough and a reflection in the mid
and low levels will move in. However, at the surface, moisture
will be below normal. Nevertheless, some passing showers can be
seen in the vicinity of the Virgin Islands and eastern Puerto Rico
at times too. Then, by mid-week, the surface high pressure over
the central Atlantic will cause the trade winds to be oriented
from the south-southeast. Moisture will begin to lift from
the Caribbean Sea, once again increasing the potential for showers
and thunderstorms.

&&

.AVIATION...
(06Z TAFs)

Mainly VFR conds expected across all terminals during the next 24
hrs. HZ due to moderate to locally high concentrations of Saharan
dust will continue to filter into the area today reducing VIS across
all local terminals to 6SM thru 20/23Z. Southeasterly winds will
continue to prevail btw 12-16 kt, with higher gusts and sea breeze
variations.

&&

.MARINE...
Light to moderate southeasterly winds will continue through
midweek, becoming east-northeast from Thursday onward. A strong
tropical wave is expected to approach the eastern Caribbean on
Friday, increasing thunderstorm activity in general through Saturday.
A long period northerly swell from distant Hurricane Erin will
arrive late Friday and into the weekend, resulting in hazardous seas
for the Atlantic waters and passages.

&&

.BEACH FORECAST...

The rip current risk will be low to moderate today. However, by
the end of the week, a northerly swell will arrive, increasing the
risk to high for most beaches in northern Puerto Rico, and also in
the northern Virgin Islands. Dangerous breaking waves can be
expected as well for the weekend and early next week.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning from 9 AM this morning to 5 PM AST this
     afternoon for PRZ001>005-007-008-010-011.

     Heat Advisory from 9 AM this morning to 5 PM AST this afternoon
     for PRZ012-013.

VI...Heat Advisory from 9 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...GRS
LONG TERM....ERG