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720
FXCA62 TJSJ 100820
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
420 AM AST Thu Sep 10 2026

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

.KEY MESSAGES...
Issued at 420 AM AST Thu Sep 10 2026

- A tropical wave moving across the area will promote showers and
  thunderstorms through the afternoon, with a limited flooding
  threat.

- High to locally very high concentrations of Saharan dust will
  spread across the region later today and persist through Sunday,
  bringing hazy skies, reduced visibility, deteriorated air
  quality and dry conditions.

- Warmer conditions expected Friday and Saturday, with elevated
  to significant heat risk possible. Isolated afternoon showers
  will remain possible.

- Moderate risk of rip currents expected today and tonight along
  most beaches, as breezy to locally windy conditions continue.
  Small Craft Operators should exercise caution, and beachgoers
  should continue to monitor beach conditions.

&&

.Short Term(Today through Saturday)...
Issued at 420 AM AST Thu Sep 10 2026

A tropical wave brought an active night with showers and
thunderstorms that affected portions of the north-central, and the
eastern and southern half of Puerto Rico, with frequent
lightning, locally heavy rain and gusty winds in some areas. Some
showers and thunderstorm persists in some areas of southeastern
Puerto Rico and near the U.S. Virgin Islands. A few Special
Weather Statements were issued for some of those areas. Some
maximum wind gusts reports from those thunderstorms include 43mph
in Isla Magueyes and Cabo Rojo. Between 1 and 2.5 inches of rain
were reported in areas or Arecibo, Barceloneta, Florida, Manati,
Vega Baja, Barranquitas and Orocovis, where Flood Advisories were
in effect. Minimum temperatures were in the low 80s in urban
areas, eastern Puerto Rico, Vieques, Culebra and the U.S. Virgin
Islands, in the mid to upper 70s along the southern, western and
northern coasts of Puerto Rico and in the mid 60s to low 70s
across the interior areas of Puerto Rico.

The bulk of the moisture from the tropical wave is expected to
move out west to southwest of our local area late this morning,
but seasonal precipitable water values between 1.7 to 1.9 will
persist throughout the day today. Therefore, additional shower and
thunderstorm activity is possible throughout the day, especially
over the eastern and southeastern half of Puerto Rico, with more
limited activity over the U.S. Virgin Islands (USVI) as the day
progresses. In the afternoon hours, showers and thunderstorms
could develop over the interior, west and northwestern Puerto
Rico, as well as downwind from El Yunque into portions of the
metropolitan area. The 500mb temperatures will be around -7
degrees Celsius today, which is favorable for convective activity,
and hence some of the thunderstorms could be locally strong with
gusty winds and frequent lightning. However, since the east-
southeasterly steering winds are stronger than normal and later
today we will have the entrance of higher concentrations of
Saharan dust, more limited activity is expected and we are not
expecting a significant rainfall event. However, a limited flood
risk will be present due to the potential of ponding of water in
roadways and poorly drained areas, especially in areas that have
received rainfall activity over the past few days. In terms of the
heat for today, even though we are expecting additional shower
activity in some areas, areas that don`t experience rainfall could
experience limited to possibly elevated heat risk. A Heat
Advisory could be issued later today; please continue to monitor
the forecast for any updates.

As moisture from the tropical wave departs the area later today
and tonight, a much drier air mass accompanied by a denser plume
of the Saharan Air Layer (SAL) will encompass the region with high
concentrations of dust. This will lower the precipitable water
values to around 1.7 tonight and around 1.5 tomorrow, Friday,
which is well below normal for this time of the year. Therefore,
some passing showers are still possible tonight over portions of
eastern Puerto Rico and the USVI, but much drier conditions are
expected for tomorrow and Saturday.

These high, to locally very high, concentrations of Saharan Dust
will persist tomorrow, Friday, and Saturday. The SAL will also
promote hazy skies, deteriorated air quality, reduced
visibilities, in addition to the much more limited shower
activity. We suggest citizens and visitors to continue to monitor
conditions as the evolve and follow the recommendations of health
officials. Additionally, warmer conditions are expected for
tomorrow and Saturday due to more limited shower activity with
elevated to significant heat risk possible both days. Warmer
nights are also expected due to heat trapping by the SAL. Even
under these conditions, diurnal heating combined with local effect
and available moisture can result in some isolated showers and
over portions of the interior and western Puerto Rico each
afternoon.

Breezy to locally windy conditions will prevail through Saturday,
especially along coastal and exposed areas, due to a surface
high-pressure north of the area.

&&

.Long Term(Sunday through Thursday)...
Issued at 420 AM AST Thu Sep 10 2026

The surface high-pressure will continue to promote easterly
breezy winds across the islands for most of the forecast period.
From Saturday night, dust concentrations are expected to diminish
as a result of the Saharan Air Layer (SAL) exiting the area.
Precipitable water values (PWAT) will briefly reach seasonal
values on Sunday and Monday morning, varying between 1.75 to 2.00
inches.

Current model guidance shows a drier air slot moving across the area
on Monday afternoon. These drier conditions will persist until
Tuesday afternoon, with PWAT values returning to seasonal values by
the evening and exceeding two inches by the end of the workweek. A
tropical wave is expected to approach the islands following the
aforementioned drier air slot. A more robust wave, is anticipated to
reach the islands from Thursday night into Friday.

The transition to wetter conditions supported by daytime heating,
local effects and the consecutive tropical waves over the CWA could
bring an increase to the chance of showers and thunderstorms across
the islands, especially through the end of the workweek. This could
potentially trigger an elevated flood risk across portions of the
islands. We advice residents and visitors to continue monitoring the
forecast as adjustments and updates become available.

&&

.AVIATION...
(06Z TAFS)
Issued at 420 AM AST Thu Sep 10 2026

Mainly VFR conditions. A tropical wave will increase SHRA and -TSRA
over the region through the afternoon. Locally induced VCTS/-TSRA
can develop and affect TJBQ btwn 08/17-21z. This can all result in
brief MVFR conditions. Saharan Dust will result in HZ/ reduced VIS
and reach high concentrations this afternoon and tonight. Winds up
to around 10 to 15 kts, with stronger gusts, through 10/13z, then
ESE at up to around 15 to 20 kt, with sea breeze variations and
stronger gusts (locally higher near SHRA/TSRA).

&&

.MARINE...
Issued at 420 AM AST Thu Sep 10 2026

A surface high pressure strengthening across the central Atlantic
will promote moderate to fresh winds, with stronger gusts through
rest of the week into the weekend. This will result in choppy to
locally rough marine conditions. Seas of around 5 to 6 feet across
most waters and local passages, with occasional seas up to 8 feet
across the offshore waters. A fast-moving tropical wave will promote
showers and thunderstorms across the regional waters this morning,
followed by afternoon thunderstorms across western waters of Puerto
Rico. Gusty winds, brief periods of torrential rainfall, and locally
higher seas are expected with the heaviest rain.

&&

.BEACH FORECAST...
Issued at 420 AM AST Thu Sep 10 2026

There is a moderate risk of rip currents along most beaches of
Puerto Rico and U.S. Virgin Islands today. Similar conditions are
expected to persist through the end of the week into the weekend due
to breezy winds and building seas across the local coastal waters.
That means life-threatening rip currents are possible in the surf
zones, and beachgoers are urged to exercise caution. The risk will
slightly begin to decrease by early next week.

A passing tropical wave will likely bring afternoon showers and
thunderstorms across northwestern beaches of Puerto Rico. Heat will
remain an additional concern, beachgoers should remain hydrated and
limit prolonged sun exposure, and seek shelter whenever they hear
thunder.

&&

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

$$

SHORT TERM/KEY MESSAGES...KML/MRR
LONG TERM...JCP
MARINE/BEACH FORECAST...YZR
AVIATION...MRR

NWS SJU Office Area Forecast Discussion