218
FXCA62 TJSJ 241449
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1049 AM AST Sun Aug 24 2025

.UPDATE...

Seas will continue to build between 6 and 8 feet across portions
of the Atlantic waters and Caribbean Passages today. The offshore
buoy 41043 indicated the swell peaking at 9 feet and 13 seconds
early this morning, and the Rincon and San Juan buoys were at 5
feet and 14 seconds. Swell decay from the offshore buoy suggest
that seas could build up to 8 feet across the nearshore waters by
late this afternoon. Therefore, the High Surf Advisory was
extended through at least Monday, and the Small Craft Advisory
(SCA) for the eastern and coastal waters of PR and the USVI is
now in effect. Also, the offshore Caribbean waters (AMZ733) were
added to the SCA, starting on Monday morning as seas and winds are
expected to reach SCA criteria due to the passage of AL99 over
the Caribbean Sea, well south of the local area. SCA conditions
are now expected to continue through at least Tuesday.

The short-term weather forecast remains on track from previous
discussion below. Thunderstorm activity is expected to develop
mainly over portions of western/southwestern PR this afternoon.


&&

.AVIATION...

(12z TAFs)

Mainly VFR conds expected across all terminals. HZ due to Saharan
dust will gradually increase today, with the event peaking tonight
into Monday morning. The 24/12z TJSJ sounding indicated east winds
up to 15 kt blo 2000 ft. TEMPO MVFR conds are possible at
TJBQ/TJPS due to locally induced afternoon TSRA.


&&

.PREV DISCUSSION... /issued 457 AM AST Sun Aug 24 2025/

KEY MESSAGES...

* The heat threat will continue today, with Extreme Heat Warnings in
  effect for Puerto Ricos coastal and urban areas, and Heat
  Advisories for Vieques, Culebra, and the U.S. Virgin Islands.
  Dangerous heat indices are expected; stay hydrated, avoid
  prolonged sun exposure, and check on vulnerable individuals.

* Long-period northerly swells will maintain hazardous marine
  conditions, high rip current risks, and large breaking waves
  through early this week. High Surf Advisories and High Rip Current
  Risk Statements remain in effect for Puerto Rico and the U.S.
  Virgin Islands.

* Hazy skies and poor air quality from Saharan dust will prevail
  today through at least early Tuesday. Isolated strong
  thunderstorms may develop this afternoon across western Puerto
  Rico, with localized flooding, lightning, and gusty winds possible.

* For the U.S. Virgin Islands, hot and hazy conditions will
  prevail, with a Heat Advisory in effect.

SHORT-TERM...Today through Tuesday...

Overnight conditions remained mainly calm, with only isolated
showers detected over regional waters and no rainfall reported on
land. Winds were light and variable, allowing for possible patchy
fog across interior valleys. Temperatures stayed exceptionally warm,
with overnight lows in the low 80s across coastal Puerto Rico,
Vieques, Culebra, and the US Virgin Islands, driven by sea surface
temperatures of 8587F.

Today, the weather is expected to continue stabilizing as an upper-
level trough departs and a ridge of high pressure builds in.
However, lingering tropical moisture, Saharan dust, warm seas, and
an east-southeasterly breeze will continue to dominate the
conditions. These factors will bring intense heat, prompting an
Extreme Heat Warning for Puerto Ricos coastal and urban areas, as
well as a Heat Advisory for Vieques, Culebra, and the US Virgin
Islands. Hazy skies, poor air quality, and breezy conditions are
also expected along exposed coasts. Isolated strong thunderstorms
may develop this afternoon over western Puerto Rico, producing
localized flooding, lightning, and gusty winds.

Tonight will remain mostly quiet but warm and hazy, setting the
stage for a very hot, dry, and stable Monday. Heat alerts will
likely continue, and air quality may worsen due to moderate to high
levels of Saharan dust. By Monday night into Tuesday, a tropical
wave (AL99) passing south of the area will slightly increase
moisture, raising the chance for localized afternoon showers and a
few thunderstorms. Winds will strengthen from the east before easing
later in the day. Heat and haze are expected to persist through
Tuesday.

LONG TERM...Wednesday through Sunday...

A seasonal weather pattern is expected in the long-term forecast.
Low-level moisture content will fluctuate from below-normal to near-
normal levels, as patches of moisture embedded in the trades stream
across from time to time. Dynamics aloft will remain marginal for
the most part, with weak ridging alternating with periods of
troughiness throughout the forecast period. As a result, 500 mb
temperatures will remain near climatological normals, while 700500
mb lapse rates could be slightly steeper toward the end of the
period.

At the surface, a high-pressure system over the central Atlantic
will promote easterly winds during the first part of the long-term
period, gradually shifting east-southeasterly toward the weekend.
This overall setup will maintain a seasonal weather pattern, with
occasional passing showers moving across windward coastal areas
during the night and morning hours. In the afternoons, showers and
thunderstorms are expected to develop over interior and
western/northwestern Puerto Rico as sufficient instability and low-
level moisture combine with diurnal heating and orographic lift.
Meanwhile, the southern coastal hills of Puerto Rico will likely
observe limited shower activity. In contrast, interior and
western/northwestern Puerto Rico may experience localized to
elevated flooding threats each afternoon, mainly resulting in urban
and small stream flooding, particularly in flood-prone areas.

In addition, the southeasterly winds will promote warm air advection
across the region. Model guidance suggests 925 mb temperatures and
1000850 mb thickness values will remain well above normal through
the weekend. This pattern will support hot surface temperatures, and
when combined with sufficient low-level moisture, could result in
sweltering heat indices and an elevated heat threat for the period.
As a result, the issuance of Extreme Heat Warnings or Heat
Advisories cannot be ruled out. Residents and visitors are advised
to stay hydrated, avoid prolonged exposure to the sun during peak
hours, take frequent breaks if working outdoors, and check on
vulnerable populations such as the elderly, children, and those with
chronic health conditions.

AVIATION...
(06Z TAFs)

VFR conditions will prevail across all local terminals; however,
afternoon SHRA/TSRA may approach TJBQ and TJPS, particularly between
24/17-23Z, bringing a slight chance of MVFR conditions. Winds will
be light and variable early, increasing to 10-15 knots with
occasional stronger gusts after 24/13Z, before diminishing again to
5-10 knots after 24/22Z. Additionally, the arrival of a Saharan Air
Layer will result in reduced visibility throughout the day.

MARINE...
A long period northerly swell will continue to spread across the
islands through early this week, resulting in hazardous seas for the
Atlantic waters and local passages. Another tropical wave will move
into the Caribbean by late tonight, moving mainly to the south of the
USVI and PR through Tuesday. This will result in moderate to fresh
easterly winds and choppy to rough seas, particularly across the
Caribbean waters.

BEACH FORECAST...

Offshore buoys 41046 and 41043 continue to indicate a long-period
northerly swell that will persist across the Atlantic waters today
through early this week. Nearshore buoys are already detecting
swells with periods of 1214 seconds. As a result, hazardous beach
conditions are expected, including a high risk of rip currents and
large breaking waves that could create dangerous swimming conditions
and minor beach erosion.

Accordingly, High Surf Advisories and High Rip Current Risk
Statements are in effect for Puerto Rico and the U.S. Virgin
Islands. For more details, please refer to CFWSJU and SRFSJU.
Beachgoers are strongly advised to exercise caution, avoid swimming
in high-risk beaches, and heed the advice of local lifeguards and
authorities.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Tuesday afternoon for PRZ001-002-
     005-008-010-012-013.

     High Surf Advisory until 6 PM AST Monday for PRZ001-002-005-008-
     010-012.

     Extreme Heat Warning until 5 PM AST this afternoon for
     PRZ001>005-007-008-010-011.

     Heat Advisory until 5 PM AST this afternoon for PRZ012-013.

VI...High Rip Current Risk through Tuesday afternoon for VIZ001-002.

     High Surf Advisory until 6 PM AST Monday for VIZ001.

     Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...Small Craft Advisory until 6 PM AST Tuesday for AMZ711-712-716-
     723-741-742.

     Small Craft Advisory from 6 PM this evening to 6 PM AST Tuesday
     for AMZ726.

     Small Craft Advisory from 6 AM Monday to 6 PM AST Tuesday for
     AMZ733.

&&

$$

UPDATE...DSR