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665
FXCA62 TJSJ 230726
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
326 AM AST Tue Jun 23 2026

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

.KEY MESSAGES...
Issued at 310 AM AST Tue Jun 23 2026

* A decrease in Saharan Dust concentrations is forecast for today.
  Moderate concentrations of Saharan Dust will return late
  tonight while high concentrations arrive by late tomorrow
  afternoon and persist through Friday. This will result in hazy
  skies, reduced visibility and deteriorated air quality.

* A weak tropical wave will move mainly south of the region (along
  with the Saharan Dust) between tomorrow and Thursday, bringing
  an additional chance for showers and t-storms.

* A moderate risk of rip currents will continue at most exposed
  beaches today and through much of the week due to persistent
  moderate to locally breezy winds.

&&

.Short Term(Today through Thursday)...
Issued at 310 AM AST Tue Jun 23 2026

Surface high pressure over the Atlantic will continue to result in
breezy, to locally windy, conditions today and throughout the
short term period. 925 mb wind speeds are forecast to continue at
above normal values for this time of the year. Precipitable water
(PWAT) should fluctuate from below normal to normal values for
this time of the year today as patches of drier air and moisture
filter over the region. An increase to more normal PWAT is then
forecast this evening and throughout at least early Thursday as
the moisture field from a tropical wave moves over the region.
Model guidance continues to suggest that the bulk of the moisture
from this wave will likely stay over Caribbean waters south of the
local islands. Like the recent tropical waves, this one will also
be embedded in Saharan Dust concentrations. Below normal PWAT is
then forecast by Thursday with only patches of moisture arriving
from time to time. In the mid to upper levels, mid-level ridging
will continue to promote subsidence and limit cloud growth as warm
500 mb temperatures continue (above normal). This, along with the
Saharan Dust will serve to limit shower and t-storm activity. An
upper low will stay well northeast then north of the region. Trade
wind showers will continue to reach windward sectors from time to
time, especially during the overnight and morning hours, being
somewhat enhanced by the moisture field from the tropical wave.
Afternoon convection will affect mainly interior W to SW Puerto
Rico today, mainly due to diurnal heating and local effects while
then affecting interior to W to NW Puerto Rico tomorrow afternoon
and (although more limited due to the saharan dust and below
normal PWAT) Thursday. An elevated heat risk will persist during
the period, with heat indices surpassing 108 degrees Fahrenheit,
especially tomorrow and Thursday. 925 mb temperatures today
suggest more below normal to normal temperatures under more E-ENE
flow, while E to ESE flow results in high-end normal to above
normal 925 mb temperatures. Heat Advisories can be issued later
today and/or during the short term period as highs over urban and
lower elevations continue in the upper 80s to lower 90s.

A decrease in Saharan Dust concentrations is forecast for today
and also suggested by model guidance. Concentrations are forecast
to range from low to locally moderate, resulting in clearer skies
today. During the overnight hours into early tomorrow, however,
the leading edge of another Saharan Air Layer (SAL) will once
again increase concentrations to moderate as it arrives along with
the above mentioned tropical wave, resulting in hazier skies
tomorrow and Thursday. Air quality and visibility are projected to
further deteriorate as current model guidance suggests that up to
high concentrations of Saharan Dust will arrive late tomorrow
afternoon as the bulk of the SAL moves over the region, these high
concentrations will then persist throughout the rest of the short
term period and on Friday. This will result in hazy skies,
reduced visibility and deteriorated air quality. Sensitive groups
should follow medical recommendations, particularly Wednesday
afternoon through Friday.

&&

.Long Term(Friday through Tuesday)...
Issued at 310 AM AST Tue Jun 23 2026

Variable conditions will prevail in the long-term forecast, with the
highest flood potential on Saturday. The broad surface high pressure
over the Central Atlantic may weaken as an upper-level low northeast
of the CWA induces a surface trough, reducing the local pressure
gradient and causing winds to become light from the northeast
through Saturday. Due to lingering moderate to high concentrations
of SAL over the region and PWAT values below climatological normal
(1.4 and 1.6 inches), weather activity should remain limited on
Friday, with shallow afternoon convection over the
western/southwestern portion of Puerto Rico. From the latest model
guidance, PWAT values may increase to seasonal values (1.6 and 1.8
inches), as the induced trough approaches the local area. Taking a
look at the latest model cross-section, theres a rise in the 850-
700 mb RH, though the 700 - 500 mb layer remains dry. Additionally,
the latest model solution shows warmer-than-normal temperatures (500
mb temperatures above -6 degrees Celsius), while the Galvez-Davison
Index (GDI) suggests the potential of isolated thunderstorms.
Although these conditions arent optimal for deep convection and the
trough should remain north of the CWA, the combination of local
effects, daytime heating, available moisture, and weak winds could
bring afternoon showers and isolated thunderstorms over the western
side of Puerto Rico. Rainfall accumulations may lead to ponding of
water over roadways, urban, and poorly drained areas, including
minor flooding. As the induced trough migrates northwestward and
winds strengthen from the southeast, a drier air mass should filter
into the region on Sunday, limiting once again shower activity.
However, a tropical wave may approach the Caribbean Basin and
increase low-level moisture content across the local islands, though
theres uncertainty introduced to the forecast as low to moderate
concentrations of Saharan Dust may weaken it and limit shower
activity.

Under a southeasterly, Sunday may be the hottest day of the period,
with warmer-than-normal 925 mb temperatures and available moisture
that could make heat indices exceed 100 degrees Fahrenheit and pose
a threat. Hence, a Heat Advisory may be issued if required.

&&

.AVIATION...
(06Z TAFS)
Issued at 310 AM AST Tue Jun 23 2026

The SAL will continue to decrease, with visibilities increasing
after 23/13Z. SHRA/VCSH developing along the Cordillera and W to
SW PR at around 23/16-22z. Passing SHRA/VCSH over windward sectors
at times. Winds will be calm to light and variable overnight, and
after 23/13z, E to ENE winds at 10-20 kt, with gusts up to 30 kt,
and sea breeze variations.

&&

.MARINE...
Issued at 310 AM AST Tue Jun 23 2026

A broad surface high pressure system over the central Atlantic
will maintain moderate to fresh easterly to east-southeasterly
winds through the next several days, resulting in choppy seas
across most of the local waters. Therefore, small craft should
exercise caution. Moderate concentrations of Saharan Dust will
return late tonight while high concentrations arrive by late
tomorrow afternoon and persist through Friday.

&&

.BEACH FORECAST...
Issued at 310 AM AST Tue Jun 23 2026

A moderate risk of rip currents remains in effect for most local
beaches, including northern and eastern Puerto Rico, Vieques,
Culebra, and portions of the U.S. Virgin Islands, while a low risk
persists for the western coasts of Puerto Rico. Life-threatening rip
currents remain possible. Moderate concentrations of Saharan Dust
will return late tonight while high concentrations arrive by late
tomorrow afternoon and persist through Friday. An elevated heat
risk will also persist, possibly through the rest of the week.

&&

.FIRE WEATHER...
Issued at 310 AM AST Tue Jun 23 2026

A Fire Danger Statement has been issued for today across portions
of the coastal plains and hills of southern and southwestern
Puerto Rico, Vieques and St. Croix due to the combination of
critically dry fuels, sustained winds of 15 to 20 mph with gusts
up to 30 mph, and minimum relative humidity values in the 40s and
low 50s. Prolonged rainfall deficits, abnormally dry to moderate
drought conditions, and critically dry fuels also continue.These
conditions will favor rapid wildfire ignition and extreme fire
behavior, meaning any fires that develop will likely spread
quickly and become difficult to contain. Outdoor burning is highly
discouraged. Afternoon convection over interior to W-SW Puerto
Rico could provide some relief this afternoon over those sectors,
however for the rest of the above mentioned areas elevated fire
weather conditions are forecast to persist.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

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

NWS SJU Office Area Forecast Discussion