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127
FXCA62 TJSJ 251900
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
300 PM AST Tue Aug 25 2026

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

.KEY MESSAGES...
Updated at 210 PM AST Tue Aug 25 2026

* An Extreme Heat Warning is in effect for portions of Puerto Rico
  this afternoon, with dangerously hot conditions expected. The heat
  threat will remain elevated throughout the period.

* A weak tropical wave will continue to promote showers and
  thunderstorms this afternoon, with a limited flooding risk, mainly
  across interior and northwestern Puerto Rico.

* Saharan dust will increase tonight into Wednesday, promoting hazy
  skies and reduced rainfall coverage across Puerto Rico and the US
  Virgin Islands.

* A tropical wave will bring deeper moisture Friday night into the
  weekend, with Saturday having the greatest potential for increased
  rainfall.

* The risk of rip currents will increase to moderate from
  Wednesday onward, particularly along northern and eastern-
  exposed beaches.

&&

.Short Term(This evening through Thursday)...
Issued at 210 PM AST Tue Aug 25 2026

Mostly fair weather conditions prevailed during the morning hours,
with a few showers moving across the regional waters and the eastern
portions of Puerto Rico and the U.S. Virgin Islands, while the
western side of the CWA remained mostly clear with minimal cloud
cover. The latest satellite-derived products show a tropical wave
moving into the region, with an area of high moisture content
reflected over the low and mid levels. Additionally, the 12z RAOB
reported abundant moisture content, with PWAT values around 1.97
inches, mainly concentrated in the low levels (RH values around
85%). Meanwhile, the sounding shows slightly drier mid levels (RH
values around 63%), though BHP-ALPW products show an increase in
the 700- 500 mb layer. Around 11 PM AST, local streamers began to
develop and produced isolated to scattered showers across portions
of the U.S. Virgin Islands and eastern Puerto Rico, including the
San Juan Metro Area. Based on the latest WSR-88D rainfall
estimates, accumulations ranged between 0.50 and 0.70 inches, with
isolated 0.90 values, over San Juan and Guaynabo. On the other
hand, showers and isolated thunderstorm over interior and
northwestern Puerto Rico left up to 1.0 - 1.50 inches over Anasco
and Moca. In terms of heat, temperatures increased during the
morning, with stations reporting upper 80s and low 90s and heat
indices exceeding 100 degrees Fahrenheit (ASOS at the LMM
International Airport reporting a preliminary maximum temperature
of 92 degrees Fahrenheit). Although convection activity already
began, elevated to significant heat conditions continue across the
CWA, with the Heat Advisory and Extreme Warning in effect until 5
PM AST.

Variable conditions will continue in the short-term forecast. The
latest satellite-derived products show a slightly drier airmass along
with moderate to high concentrations of Saharan Dust. Model
guidance suggests PWAT values diminishing briefly to near below
climatological normal (around 1.6 inches), with low and mid level
moisture content dropping to 20 - 40%. Although conditions seem
unfavorable for deeper convection, the combination of the
available moisture, daytime heating, and local effects should
enhance shower activity across interior and western/southwestern
Puerto Rico. Rainfall accumulations will likely remain minimal,
though isolated areas can expect ponding of water over roadways
and poorly drained areas. Due to the influence of Saharan Dust,
isolated thunderstorms cannot be ruled out. Followed by the
afternoon convection, winds will likely shift from the E-ENE as a
surface trough north of the CWA approaches the area and increases
moisture content by late Wednesday night into Thursday. Looking at
the latest guidance`s cross-section, moisture content should
increase in the low levels, with the 850 - 700 mb layer up to 70 -
80%. Although the most enhanced activity of the trough may stay
north of the CWA, enough instability combined with local effects
and available moisture will increase the likelihood of showers and
isolated thunderstorms over windward sections of the islands
during the morning, followed by afternoon convection over interior
and western Puerto Rico. Although widespread flooding is not
expected, rainfall accumulations could lead to minor flooding over
flood-prone areas. Weather conditions should gradually improve by
Thursdays evening as a drier airmass filters into the region,
with limited shower activity.

Heat remains as the primary threat across the CWA, as warmer-than-
normal temperatures are anticipated across the islands.
Additionally, the presence of SAL will likely inhibit effective
nighttime cooling and allow warmer-than-normal minimum
temperatures. With the available moisture, heat indices across
urban and low-lying areas of the islands can still exceed 100
degrees Fahrenheit, increasing the heat threat and affecting
mainly sensitive groups without effective cooling and/or
hydration. Therefore, heat products (Advisory/Warning) will likely
be issued.

&&

.Long Term(Friday through next Monday)...
Issued at 309 AM AST Tue Aug 25 2026

Patches of moisture with seasonal precipitable water (PWAT) values
will move across the islands on Friday under a generally easterly
steering flow to start the long term period, bringing in showers
over windward sectors to start the morning hours. Diurnal heating,
sea breeze convergence and local effects will also result in
afternoon showers and t-storms over mainly western Puerto Rico.
Available moisture however will be mostly limited to the lower
levels.  An elevated heat risk is also possible over urban and
coastal sectors.

A tropical wave, and its associated moisture field, will then
approach the islands Friday night and push PWAT values to above
normal, above 2 inches, through at least the overnight hours
Saturday into Sunday. Available moisture can also reach deeper in
the atmosphere, further prompting a flooding risk. Steering flow
will be generally ESE and can result in showers and possible t-
storms moving over the islands during the overnight and morning
hours, while afternoon showers and t-storms are forecast to develop
over interior to W-NW PR as well as downwind of the local islands
and El Yunque. This period is forecast to be the most humid and the
most likely to feature increased rain chances.

Drier air is then forecast to move over the area on Sunday,
resulting in below normal PWAT values and, according to the latest
guidance, more moderate Saharan Dust concentrations moving over the
area as available moisture is once again confined to the lower
levels. Afternoon convection is still forecast over W to NW under
ESE steering flow. Uncertainty increases to start the next workweek
due to the tropical wave AL96 currently over the eastern tropical
atlantic (please see the latest Tropical Weather Outlook for the
most up to date information regarding this wave). The current
forecast is based on generally easterly steering flow veering to
become more south-southeasterly and steering patches of moisture and
drier air over the islands, with showers moving over windward
sectors and afternoon convection develops. Given forecast
uncertainties, residents and local interests are advised to track
upcoming updates as AL96 moves over the Atlantic. Seasonal to above
seasonal 925 mb temperatures will persist during the period and
result in elevated to possibly significant heat risks each day, with
the highest chances of a more limited heat risk being on Saturday.

&&

.AVIATION...
(18Z TAFS)
Issued at 210 PM AST Tue Aug 25 2026

Mainly VFR conds will prevail across all terminals, though aftn
convtn producing -TSRA will likely reduce CIGs/VIS across JBQ,
leading to brf MVFR conds btwn 25/18-20z. Meanwhile, VCTS should
continue across JPS while JSJ, IST, and ISX can expc mainly typical
VCSH through 25/22-23z, with SAL concentrations leading to HZ and
reducing VIS. Winds from the E-ESE should weaken and become VRB btwn
5 - 10 kts by 25/23z, strengthening once again btwn 12 - 15 kts
and gusts up to 25 kts.

&&

.MARINE...
Issued at 210 PM AST Tue Aug 25 2026

Surface high pressure extending across the western and central
Atlantic will continue to support moderate east to east-
southeasterly winds across the regional waters, becoming locally
fresh at times. Increasing moisture associated with a tropical wave
will promote additional shower and thunderstorm development across
the western local waters and Mona Passage into tonight. Locally
higher winds, choppy seas, and reduced visibility can be expected in
and around thunderstorms. Saharan dust concentrations will increase
tonight and peak on Wednesday, resulting in hazy skies and slightly
reduced visibility. A weak long-period northerly swell remains
forecast to arrive and spread across the regional waters by Thursday.

&&

.BEACH FORECAST...
Issued at 210 PM AST Tue Aug 25 2026

A low risk of rip currents will continue through at least tonight
across the local islands. Nonetheless, beachgoers should exercise
caution, as life-threatening rip currents can still occur near
jetties, reefs, groins, and piers.

By Wednesday, a gradual increase in winds and seas will likely
result in a moderate risk of rip currents, particularly along the
northern and eastern-exposed beaches of the islands. The moderate
risk is expected to continue through the end of the week.

Increasing moisture associated with a tropical wave will support
showers and isolated thunderstorms across the regional waters and
coastal areas this afternoon, mostly across northwestern portions of
Puerto Rico. Beachgoers should remain weather alert, as
thunderstorms could produce gusty winds and dangerous lightning.

&&

.FIRE WEATHER...
Issued at 210 PM AST Tue Aug 25 2026

A marginal fire weather risk will continue through the remainder of
today, mainly due to the presence of dry fuels. Although relative
humidity values may briefly decrease during peak heating, increasing
tropical moisture associated with a passing tropical wave should
generally keep RH above critical levels. Overall, the combination of
higher moisture should limit the potential for rapid fire spread and
keep the overall fire weather threat marginal for the rest of the
afternoon. &&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...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...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM/AVIATION...MNG
LONG TERM...MRR
MARINE/BEACH FORECAST/FIRE WX...CVB

NWS SJU Office Area Forecast Discussion