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912
FXCA62 TJSJ 111901
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
301 PM AST Mon May 11 2026

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

.KEY MESSAGES...
Issued at 300 PM AST Mon May 11 2026

* Warm to hot conditions will persist through much of the week
  across the islands. Heat indices are expected to exceed 100
  degrees across urban and coastal areas of Puerto Rico and the U.S.
  Virgin Islands, with a moderate to locally elevated risk of heat-
  related impacts.

* Additional heat products, including Heat Advisories, may become
  necessary later this week if current trends continue.

* Passing showers will continue to affect windward and eastern
  sections during the overnight and morning hours, followed by
  afternoon convection across western and interior Puerto Rico.

* Marine and coastal conditions will remain hazardous at times due
  to persistent choppy seas and a moderate risk of rip currents
  along north- and east-facing beaches of Puerto Rico and the U.S.
  Virgin Islands through at least midweek.

* A minor concentration of Saharan dust is forecast to arrive by
  midweek into late week, resulting in hazy skies and possible
  reductions in air quality and visibility for sensitive groups.

&&

.Short Term(This evening through Wednesday)...
Issued at 300 PM AST Mon May 11 2026

A surface high over the central Atlantic will promote breezy, to
locally windy, east to east-southeast winds throughout the period as
it continues to tighten the local pressure gradient. Unsecured
objects could blow around. Current satellite derived precipitable
water (PWAT) imagery indicate a patch of moisture reaching the area
from the east with PWAT values of 1.4 to 1.6 inches over the eastern
and northern region. Low PWAT values (1.1 to 1.2 inches) are still
observed over south-central to southwestern PR where elevated fire
weather conditions continue (RFDSJU). Above mentioned steering flow
will bring patches of both moisture and drier air towards the
islands, prompting precipitable water (PWAT) values at below normal
to normal values, reaching more normal values on Wednesday as more
broad moisture reaches the region on Monday. A mid to upper level
ridge pattern will promote subsidence aloft and inhibit widspread
shower and t-storm activity. However, passing shower activity will
continue to be steered towards windward sectors of the islands
during the morning and overnight hours while diurnal heating and
local effects will still promote afternoon convection over mainly
interior to WNW PR. Afternoon lines of showers from the local
islands and El Yunque can also develop. A limited flooding risk will
persist for the short term period, particularly across interior to
WNW PR each afternoon. This can result in ponding of water over
roads and poorly drained areas and a chance of urban and small
stream flooding. East to east-southeast steering flow will continue
to promote a limited heat risk over coastal and urban areas of the
islands where heat indices are forecast to reach upper 90s to low
100s. This level of heat affects primarily those individuals
sensitive to heat, especially when outdoors without effective
cooling and/or adequate hydration. East to east-southeast flow will
also steer a mass of generally low concentrations of Saharan Dust,
particularly late tomorrow into Wednesday.

&&

.Long Term(Thursday through Monday)...
Issued at 343 AM AST Mon May 11 2026

A few changes were introduced to the long-term forecast, though no
significant flooding or lightning threats are expected. As mentioned
in the previous discussion, model guidance continues to suggest a
dry to typical weather pattern across the CWA, with a surface high
pressure over the Central Atlantic lingering and promoting SE winds
through most of the period. Additionally, another high pressure is
expected to move over the western Atlantic by Sunday, migrating
eastward and shifting winds from the E-ESE. In the mid to high
levels, a ridge will dominate most of the weather pattern through
Sunday, maintaining warmer mid-level temperatures (around -4 and -5
degrees Celsius) for this time of the year, resulting in stability
aloft and shallow convection. Nevertheless, an upper-level trough
may gradually deepen into the tropics by Sunday, weakening the ridge
and slightly introducing some instability. From the latest guidance,
PWAT values will remain seasonal (between 1.5 and 1.75 inches), with
mid-level moisture content increasing and lapse rates becoming
steeper. As a result, with breezy to locally windy conditions from
Thursday onward, passing showers will move from time to time across
windward sections of the islands, particularly during the night into
morning hours. As mentioned in the previous discussions, shallow
afternoon convection over interior and western/northwestern Puerto
Rico is expected in the long-term forecast, though the highest
potential of flooding may be seen later on Sunday into Monday,
resulting in a limited flooding and lightning risk. Nevertheless,
these areas can still expect moderate to locally strong showers,
resulting in puddles over the road, gusty winds, and reduced
visibility.

Warm-to-hot conditions will likely persist in the long-term
forecast, with winds from the southeast and available moisture
likely to result in heat indices surpassing 100 degrees Fahrenheit,
and even meet Heat Advisory Criteria, particularly over urban and
coastal areas of Puerto Rico and the U.S. Virgin Islands. Residents
and visitors should remain tuned to further updates, as these
conditions may affect most people sensitive to heat.

Based on the latest NASA DUex product, minor concentrations of SAL
are expected to arrive on Wednesday, likely to persist through the
end of the workweek. These conditions may slightly reduce visibility
and affect people sensitive to these particles.

&&

.AVIATION...
(18Z TAFS)
Issued at 300 PM AST Mon May 11 2026

Mainly VFR conditions expected to prevail. Breezy E to ESE winds
will continue to steer quick moving -SHRA/VCSH towards the terminals
through 11/23z. Possibly isolated -TSRA can form across the interior
to NW PR through 11/23z, affecting TJBQ. This can promote brief MVFR
conditions. -SHRA/VCSH will continue to be steered towards eastern
and southern terminals after 11/23z. E to ESE winds will continue at
15 to 20 kts, with higher gusts up to 20 to 30 kts, winds will
decrease, becoming lighter and variable after 12/00Z, picking up
again after 12/13z with sea breeze variations.
&&

.MARINE...
Issued at 300 PM AST Mon May 11 2026

A surface high pressure system over the central Atlantic will
continue to generate moderate to locally fresh east to southeast
winds across the regional waters through at least midweek before
gradually weakening thereafter. Seas are expected to range between 3
and 5 feet, with occasional wave heights reaching up to 6 feet. As a
result, choppy seas are expected to prevail as fresh to strong winds
affect the local waters. Additionally, a weak long-period
northeasterly swell will reach the Atlantic waters by midweek.
&&

.BEACH FORECAST...
Issued at 300 PM AST Mon May 11 2026

Breezy to locally windy conditions will continue across the region
through at least midweek, maintaining a moderate risk of rip
currents along most local beaches, particularly along north- and
east-facing coastlines.

A weak long-period northeasterly swell is also expected to arrive
across the Atlantic beaches by midweek, which could further increase
the risk of dangerous rip currents. Beach visitors are urged to swim
only at beaches with lifeguards on duty, remain aware of surf
conditions, and avoid venturing too far from shore.

If caught in a rip current, remain calm and avoid swimming against
the current. Instead, swim parallel to the shoreline until free from
the current, then make your way back to shore. If unable to escape,
float or tread water and signal for help.

For additional information, visit weather.gov/beach/sju.

&&

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

$$

SHORT TERM/AVIATION...MRR
LONG TERM...MNG
KEY MESSAGES/MARINE/BEACH...CVB

NWS SJU Office Area Forecast Discussion