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969
FXCA62 TJSJ 060827
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
427 AM AST Sun Sep 6 2026

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

.KEY MESSAGES...
Issued at 424 AM AST Sun Sep 6 2026

* Dangerous heat is expected today and again on Monday. An Extreme
  Heat Warning is in effect for Puerto Rico beginning this morning,
  with a Heat Advisory for Vieques, Culebra, and the U.S. Virgin
  Islands. Although passing showers and clouds may provide some
  temporary relief, enough sunshine is expected for heat indices to
  reach dangerous levels.

* Showers and thunderstorms will increase at times today, with the
  heaviest activity expected this afternoon across the interior and
  northwestern Puerto Rico. Locally heavy rainfall may result in
  ponding of water and localized flooding. Shower and thunderstorm
  coverage may decrease somewhat on Monday.

* A low risk of rip currents will continue across most beaches.
  However, life-threatening rip currents remain possible, especially
  near jetties, reefs, groins, and other structures.

* A much more stable weather pattern is expected by Tuesday, with
  a noticeable decrease in shower and thunderstorm activity. Trace
  amounts of Saharan dust will also be present by midweek.

&&

.Short Term(Today through Tuesday)...
Issued at 424 AM AST Sun Sep 6 2026

During the overnight hours, temperatures remained a few degrees
warmer than the previous night, allowing the region to start the day
from a warmer baseline. Well-above-normal 925-mb temperatures
associated with southeasterly flow, combined with well-above-normal
moisture, will support dangerous heat conditions later today. An
Extreme Heat Warning for Puerto Rico and a Heat Advisory for
Vieques, Culebra, and the U.S. Virgin Islands will go into effect by
mid-morning. Some uncertainty remains, as showers and isolated
thunderstorms continue to develop over the local waters early this
morning, enhanced by the tropical wave and an upper-level trough
slowly moving westward. However, this activity has not produced
widespread cloud cover, and sufficient clearing after sunrise could
still allow temperatures and heat indices to rise quickly.

For today, abundant moisture will persist as the tropical wave moves
through the region, with precipitable water values around 2.1-2.2
inches. The upper-level trough will remain nearby through this
afternoon, although it will shift farther west as ridging gradually
builds over the northeastern Caribbean. Some ventilation aloft may
therefore persist, allowing afternoon convection to become locally
stronger across the interior and northwestern portions of Puerto
Rico, where local and diurnal effects will provide additional
forcing. Streamers may also develop downwind of the local islands
and El Yunque, producing additional showers over portions of eastern
Puerto Rico and the San Juan metro area. Locally heavy rainfall will
result in ponding of water, and minor flooding in poor-drainage
areas, particularly across northwestern Puerto Rico.

A similar pattern is expected Monday, with lingering moisture and
above-normal temperatures supporting another day of dangerous heat.
Afternoon convection is also expected, mainly over the interior and
western to northwestern portions of Puerto Rico, while streamers may
once again develop downwind of the islands and El Yunque. However,
with the upper-level trough farther west and ridging aloft becoming
more established, increasing mid-level stability may reduce the
overall coverage and vertical extent of convection. Trace amounts of
Saharan dust will also be present, particularly by Monday evening.

By Tuesday, a significant drying trend is expected as the ridge
becomes firmly established over the region. Precipitable water
values and lower- to mid-level relative humidity will fall sharply
through the day, reaching well-below-normal levels by the evening.
At the same time, 500-mb temperatures will warm to well-above-normal
values, while both the 700-500 mb and, eventually, the 850-700 mb
lapse rates decrease to below-normal levels, indicating increasing
stability through a deeper layer of the atmosphere. Therefore, a
much less active weather pattern is expected, with considerably
lower shower and thunderstorm coverage by later in the day.

&&

.Long Term(Wednesday through Sunday)...
Issued at 424 AM AST Sun Sep 6 2026

A surface high-pressure will move closer to the northeastern
Caribbean, tightening the pressure gradient and resulting in breezy
to locally windy east-southeasterly winds, especially along coastal
and exposed areas. A weak tropical wave will move through the region
Wednesday, with residual moisture persisting into Thursday.
Precipitable water values are expected to increase to 2.1 to 2.3
inches, just above the 75th percentile for this time of year, and
the 500 mb temperatures are expected to decrease to near -6 to -7
degrees Celsius, supporting an increase in shower and thunderstorm
activity. However, the breezy conditions should limit the flood
potential, with little relief expected for the ongoing drought and
water-supply concerns.

A drier air mass, accompanied by low concentrations of Saharan dust,
will spread across the region Friday and Saturday. Precipitable
water values will decrease to around 1.5 inches, nearly two standard
deviations below normal, favoring mostly stable and warmer
conditions. Some uncertainty remains Friday, as the ECMWF maintains
higher moisture across the region.

By Sunday, an upper-level low and associated lower-level disturbance
may move closer to the northeastern Caribbean, gradually increasing
moisture and instability. Precipitable water values are expected to
rise to 1.6 to 1.8 inches, closer to climatological normals, while
cooler 500-mb temperatures and more favorable mid-level conditions
could further enhance instability and shower and thunderstorm
development, especially in the afternoon along the western interior
and northwestern quadrant.

Overall, the tropical wave may provide some temporary relief from
the heat Wednesday and Thursday, but warmer conditions are expected
to return late in the week and into the weekend, with limited to
elevated heat risk persisting through the period.

&&

.AVIATION...
(06Z TAFS)
Issued at 424 AM AST Sun Sep 6 2026

Mainly VFR conditions are expected to prevail across all terminals
through the fcst period. Passing -SHRA/VCSH and brief VCTS are
expected across the USVI and E PR terminals through 06/15z.
Convection may result in VCTS at TJPS aft 06/17z and tempo MVFR
conditions at TJBQ aft 16/17z, with a PROB30 for TSRA between 18-
22z. Elsewhere, mainly VCSH expected. Winds light/VRB to calm
through 06/13z, becoming E-ESE at 9-14 kt thereafter, with sea
breeze variations and stronger gusts possible near SHRA/TSRA.

&&

.MARINE...
Issued at 424 AM AST Sun Sep 6 2026

Light to moderate southeast winds are expected to continue through
at least tomorrow, Monday. From Tuesday onward, winds are expected
to become moderate to fresh as a surface high pressure strengthens
over the central Atlantic, leading to choppy seas of up to 6 feet
and east winds reaching 15 to 20 knots with higher gusts. Moisture
associated with a tropical wave will continue to bring scattered
showers and isolated thunderstorms over the regional waters today.

&&

.BEACH FORECAST...
Issued at 424 AM AST Sun Sep 6 2026

A low risk of rip currents is expected to prevail through Monday
night along all local beaches of Puerto Rico and U.S. Virgin
Islands. However, even when the risk is low, life-threatening rip
currents often occur near jetties, piers, reefs, and groins.
Beachgoers should remain cautious always. By Tuesday, the risk will
increase to moderate along the islands` northern and eastern
beaches, as winds become moderate to fresh and seas gradually build
to around 4 or 5 feet. By midweek onward, the moderate risk is
anticipated to extend to most beaches. A moderate risk means life-
threatening rip currents are possible and beachgoers are urged to
exercise caution.

Another beach hazard will be the heat. Beachgoers should remain
hydrated and limit prolonged sun exposure. Additionally, gusty winds
and lightning due to afternoon showers and isolated thunderstorms,
particularly across the western beaches of Puerto Rico. Beachgoers
should seek shelter whenever they hear thunder.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning from 10 AM this morning to 5 PM AST this
     afternoon for PRZ001>011.

     Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ012-013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM/AVIATION...CVB
LONG TERM...KML/YZR
MARINE/BEACH...YZR

NWS SJU Office Area Forecast Discussion