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983
FXCA62 TJSJ 251800
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
200 PM AST Mon Aug 25 2025

.KEY MESSAGES...

* Long period northerly swells and strong winds across the
  Caribbean waters will continue to produce hazardous seas, rough
  surf, and life-threatening rip currents across the local waters
  and coastal areas of all the islands through at least Tuesday.

* Hot temperatures will continue through the workweek,
  particularly along the northern and western coastal sections of
  Puerto Rico. Extreme Heat Warning conditions are likely on
  Wednesday and Thursday as winds turn from the southeast.

* For the U.S. Virgin Islands, breezy conditions and passing
  showers with possible isolated thunderstorms are expected
  through the evening hours. Hot temperatures will continue
  through the workweek.


&&

.SHORT TERM...Rest of today through Wednesday...

Breezy and hazy conditions prevailed across the islands through
the morning hours. Another hot day was observed across most areas
with maximum temperatures ranging from the upper 80s to low 90s
across the lower elevations of the islands with heat indices
ranging between 106F-112F before noon along most western, southern
and northern coastal sections of PR, and up to 106F across the
USVI and eastern PR. The wind was from the east between 15 to 25
mph with sea breeze variations and gusts up to 30 mph.

For the rest of this afternoon, hazy conditions will continue
across the area, however, showers and isolated thunderstorms are
still expected to develop over west/southwest PR. Meanwhile, an
active tropical wave passing south of the region is producing
strong thunderstorms over the Caribbean Sea, and some of this
activity is expected to move over our offshore Caribbean waters
(AMZ733) and Mona Passage (AMZ741) through this evening. Outflow
boundaries from these thunderstorms could produce strong wind
gusts in St. Croix and southern PR, as well across the Caribbean
waters and southern portions of the local passages.

For Tuesday, Saharan dust will diminish and winds will continue
from the east but will decrease somewhat in speed compared to
today. Afternoon showers and thunderstorms will develop along
portions of the Cordillera and western PR due to the combination
of the sea breeze convergence with daytime heating and the
available moisture content. Heat advisory conditions are expected
once again, mainly across the northern and western portions of
PR. On Wednesday, lighter winds are expected and from the
southeast, promoting hot temperatures once again across most
coastal and urban areas of the lower-elevations of the islands.
Also, slow-moving storms are expected due to the weak steering
winds, increasing the potential for urban and small stream
flooding, particularly across central and northwestern PR. Across
the USVI, hot conditions will prevail with limited shower activity
in general.


.LONG TERM...Thursday through Monday...

/From prev discussion issued at 508 AM AST Mon Aug 25 2025/

The latest model guidance indicates a slightly wetter scenario for
the beginning of the long-term period. Columnar moisture is now
forecast to increase, with precipitable water values near or above
normal levels and 700-500 mb relative humidity well above normal for
this time of year. This enhanced moisture is tied to a weak, deep-
layered trough expected to cross the region from midweek through the
end of the workweek. As this feature exits the area, low-level
southerly flow will advect additional tropical moisture into the
northeastern Caribbean, reinforcing the wetter pattern.

Upper-level dynamics will also become more favorable, as 500 mb
temperatures are expected to drop into the -6.5 to -7 C range,
values within the lower quartile of climatological normals and
therefore supportive of convective development. The Galvez-Davison
Index reflects this by showing an increasing potential and spatial
coverage shower and thunderstorm activity, particularly on
Friday, when scattered shallow convection and isolated
thunderstorms appear more likely. As a result, the risk for
localized urban and small stream flooding will be elevated both
Thursday and Friday, with the northern half of Puerto Rico most
prone due to the persistent southerly wind flow.

For the remainder of the long-term period, conditions are expected
to transition back toward a more seasonal pattern. Sufficient low-
level moisture combined with marginal instability aloft should
sustain typical diurnal activity, with passing showers over windward
coastal areas during the nighttime and morning hours, and locally
induced afternoon convection across the interior and
western/northwestern Puerto Rico, aided by sea breeze convergence.

In addition, the prevailing southerly winds will promote significant
heat concerns toward the end of the workweek and into the weekend.
With 925 mb temperatures and 1000-850 mb thickness values remaining
above normal, hot surface temperatures combined with adequate low-
level moisture may result in elevated to significant heat stress.
Therefore, the issuance of Extreme Heat Warnings cannot be ruled out.


&&

.AVIATION...

(18Z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, tempo MVFR to brief IFR conds
are possible at TJBQ thru 25/22z due to TSRA, and VCTS at TISX due
to tropical wave moving across the Caribbean Sea. The 25/12z TJSJ
sounding indicated east winds up to 37 kt blo FL080.


&&

.MARINE...

A long period northerly swell will continue to spread across the
islands through at least Tuesday, resulting in hazardous seas for
the Atlantic waters and local passages. Another tropical wave will
continue to move over the Caribbean waters today, 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...

Long period northerly swells and strong winds across the Caribbean
waters will continue to produce hazardous seas, rough surf, and
life-threatening rip currents across the local waters and coastal
areas of all the islands through at least Tuesday. Additionally,
the stronger swell energy and larger breaking waves could cause
localized coastal flooding along portions of the northern
coastline of Puerto Rico through late this afternoon.

High Surf Advisories and High Rip Current Risk Statements remain in
effect for Puerto Rico and the U.S. Virgin Islands through Tuesday,
while a Coastal Flood Advisory is in effect for the northern
coastline of Puerto Rico through this afternoon. For more
details, please refer to the latest Coastal Hazards Message
(CFWSJU) and Surf Zone Forecast (SRFSJU). Beachgoers are strongly
urged to exercise extreme caution, avoid swimming in high-risk
areas, and heed the guidance of local lifeguards and authorities.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Coastal Flood Advisory until 6 PM AST this evening for PRZ001-
     002-005-008.

     Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.

     High Rip Current Risk through late Tuesday night for PRZ001-002-
     005-008-010-012-013.

     High Surf Advisory until 6 AM AST Tuesday for PRZ001-002-005-008-
     010-012.

     High Rip Current Risk through late tonight for PRZ011.

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

     High Rip Current Risk through late Tuesday night for VIZ001-002.

     High Surf Advisory until 6 AM AST Tuesday for VIZ001.

AM...Small Craft Advisory until 6 PM AST Tuesday for AMZ711-712-716-
     723-726-733-741-742.

&&

$$

SHORT TERM...DSR
LONG TERM....CVB
AVIATION...DSR
BEACH/MARINE...DSR

NWS SJU Office Area Forecast Discussion