363
FXCA62 TJSJ 071827
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
227 PM AST Mon Sep 7 2026

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

.KEY MESSAGES...
Issued at 207 PM AST Mon Sep 7 2026

* Elevated to significant heat conditions will continue for the
  rest of the workweek, with heat indices potentially reaching
  108114F, particularly across coastal and urban areas.

* Showers and thunderstorms are expected for the rest of this
  afternoon, diminishing during the evening hours. On Tuesday,
  slightly drier conditions are expected as a drier air mass moves
  into the region, resulting in reduced shower and thunderstorm
  activity.

* On Wednesday, another tropical wave is forecast to move across the
  islands, increasing the potential for showers and a limited
  flooding threat.

* A moderate risk of rip currents is expected along the northern
  and eastern beaches of Puerto Rico, Culebra, Vieques, and the
  U.S. Virgin Islands.

&&

.Short Term(This evening through Wednesday)...
Issued at 207 PM AST Mon Sep 7 2026

Variable weather conditions prevailed during the morning hours, with
cloudiness across most of the eastern sections of the CWA and
isolated to scattered showers across the coastal waters of the U.S.
Virgin Islands. During the morning hours, the main threat across the
region was excessive heat, with heat indices reaching up to 114
degrees across portions of the north-central and southern sections
of Puerto Rico. As of 12 PM AST, showers were observed by Doppler
radar across the San Juan metropolitan area, including areas between
Loiza and San Juan. Showers quickly spread across the northern
and northwestern sections of Puerto Rico, accompanied by frequent
lightning and gusty winds across the affected areas. Several Flood
Advisories and Special Weather Statements were issued, along with
a Flash Flood Warning for the municipality of Vega Baja through
4:15 PM AST. As of 1:30 PM AST, the Extreme Heat Warning was
cancelled due to the increase in shower and thunderstorm activity
across the northern sections of Puerto Rico and diminishing heat
indices across southern sections. The increased cloud cover and
rainfall helped limit additional heating across these areas during
the afternoon hours.

For the rest of Monday afternoon into the evening hours, lingering
showers and moisture associated with the previous tropical wave will
continue to support shower and isolated thunderstorm development
across northern sections and across the local waters.  By Tuesday, a
surface high pressure strengthening over the central Atlantic,
combined with ridging at the mid and upper levels, will promote a
drier and more stable weather pattern. Precipitable water values are
expected to decrease to around 1.50 inches, while warmer
temperatures at 500 mb will further limit deep convective
development. In addition, Saharan dust particles will move across
the region, resulting in hazier skies, although concentrations
should remain generally low to moderate. The strengthening surface
high will also tighten the local pressure gradient, resulting in
increasing east-southeasterly winds across the islands and
surrounding waters.

By Wednesday, another tropical wave is expected to move across the
northeastern Caribbean, resulting in a noticeable increase in
moisture and shower activity across Puerto Rico and the U.S. Virgin
Islands. Precipitable water values will increase again as the wave
approaches, supporting passing showers across eastern sections
during the morning hours followed by afternoon convection across the
interior and western portions of Puerto Rico. Breezy east-
southeasterly winds associated with the strong pressure gradient
will continue across the area, which could help limit rainfall
accumulations despite the increase in available moisture. At upper
levels, high pressure near 250 mb will remain north of the region,
maintaining a generally favorable upper-level wind pattern. Some
Saharan dust particles may remain across the area, but the
increasing tropical moisture should favor a wetter and more variable
weather pattern compared with

&&

.Long Term(Thursday through next Sunday)...
Issued at 356 AM AST Mon Sep 7 2026

A surface high-pressure across the Atlantic will continue to promote
breezy to locally windy southeast winds on Thursday, becoming more
easterly Friday, and then east to northeasterly Saturday through
Monday. On Thursday, residual moisture from a tropical wave will
remain over the region, with precipitable water values around 1.9 to
2.2 inches, seasonal to near-above-average for this time of the year
based on climatology. Model guidance suggests that 500mb
temperatures will remain near -6 to -7 degrees Celsius, which will
likely support thunderstorm development. As a result, expect passing
showers across eastern Puerto Rico and the U.S. Virgin Islands early
in the morning, followed by afternoon convection across the western
interior to northwestern Puerto Rico. That activity will likely
cause ponding on roads and in poorly drained areas. At the moment,
those areas are being highlighted with a limited flood threat.

By the end of the week into Saturday, a drier weather pattern with
hazy skies will dominate. A drier air mass, accompanied by moderate
to locally high concentrations of Saharan dust particles, will
approach the northeastern Caribbean. Precipitable water values are
expected to drop below 1.5 inches, ranging from below normal to
nearly two standard deviations below normal. In terms of rainfall, a
few afternoon showers will remain possible across western Puerto
Rico, fueled by local effects, but shower activity should remain
limited, with no flooding concerns. Heat will be the primary hazard,
as warmer conditions are expected, along with the potential need for
heat-related products.

By Sunday into early next week, an upper-level low and an associated
lower-level disturbance may move closer to the northeastern
Caribbean, gradually increasing moisture and instability.
Precipitable water values are expected to rise to seasonal levels,
while cooler 500-mb temperatures and more favorable mid-level
conditions could further enhance instability and shower and
thunderstorm development, especially during the morning across
eastern areas and in the afternoon across the western interior and
northwestern quadrant of Puerto Rico.

Overall, residual moisture on Thursday will result in afternoon
showers and thunderstorms. However, hazy, drier, and warmer
conditions are expected to return by the end of the week and into
Saturday, followed by increasing instability from Sunday into early
next week.

&&

.AVIATION...
(18Z TAFS)
Issued at 207 PM AST Mon Sep 7 2026

Tempo MVFR to IFR conditions possible at TJSJ/TJBQ thru 07/21z due
to locally induced SHRA/TSRA. Elsewhere, mostly VCTS/VCSH
expected through the evening hours. VFR overnight through Tuesday
morning. HZ due to Saharan dust will continue to increase through
late tonight, but VSBY should remain P6SM. SE winds up to 12 kt
with sea breeze variations expected to continue through the rest
of the afternoon hours, bcmg light and variable overnight.

&&

.MARINE...
Issued at 207 PM AST Mon Sep 7 2026

Moderate easterly winds will gradually strengthen tonight into
Tuesday as a surface high pressure strengthens across the central
Atlantic. Winds of 15 to 20 knots, with higher gusts, will become
increasingly widespread from Tuesday onward, resulting in choppy to
locally rough marine conditions. Seas will generally build to 4 to 6
feet across the offshore waters and local passages, with occasional
seas up to 8 feet possible by Tuesday night and through midweek.
Passing showers will continue across portions of the regional
waters, with locally higher winds and seas possible in and near
thunderstorms.

&&

.BEACH FORECAST...
Issued at 207 PM AST Mon Sep 7 2026

Increasing easterly winds and building seas will promote a
moderate risk of rip currents tomorrow, Tuesday, mainly along the
northern and eastern beaches of Puerto Rico, Culebra, Vieques,
and the U.S. Virgin Islands. A low risk will persist along the
southern and western beaches of Puerto Rico through at least
tomorrow night. A moderate risk is forecast for most local beaches
from Wednesday onward.

Heat will remain an additional concern for beachgoers. Showers and
isolated thunderstorms may also produce brief gusty winds and
lightning, especially during the afternoons.

&&

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

$$

SHORT TERM/KEY...LIS
LONG TERM...YZR
AVIATION/MARINE/BEACH...DSR