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894
FXCA62 TJSJ 050839
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Sat Sep 5 2026

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

.KEY MESSAGES...
Issued at 433 AM AST Sat Sep 5 2026

* A wetter pattern is expected through Monday, with more frequent
  showers and a few thunderstorms. The heaviest rainfall is expected
  during the afternoon hours, particularly across interior and
  western Puerto Rico. Locally heavy rainfall could result in
  ponding of water on roads and flooding in urban and poorly drained
  areas.

* Periods of showers will also affect eastern Puerto Rico and the
  U.S. Virgin Islands, particularly during the morning and overnight
  hours.

* Dangerous heat conditions will continue through the weekend and
  into Monday. A Heat Advisory is in effect for today, with warm and
  humid conditions expected to result in significant heat impacts,
  particularly across coastal and urban areas. Cloud cover and
  showers may provide some relief at times.

* A low risk of rip currents will prevail across most beaches
  through the Holiday weekend. However, life-threatening rip
  currents can still occur where the risk is low, particularly
  near groins, jetties, reefs, and piers.

&&

.Short Term(Today through Monday)...
Issued at 433 AM AST Sat Sep 5 2026

During the overnight hours, temperatures remained around 1 to 2
degrees warmer than those observed during the same time frame
yesterday. Showers and isolated thunderstorms developed along a
narrow northwest-to-southeast oriented band associated with the
leading edge of moisture from a broad tropical wave, some of this
activity moved over eastern portions of Puerto Rico. For today,
above-normal 925-mb temperatures continue to support an elevated
heat threat, with conditions potentially approaching Extreme Heat
Warning criteria. However, lingering cloud cover could limit daytime
heating during the morning hours. Therefore, the Heat Advisory
remains in effect, but conditions will be monitored in case an
upgrade becomes warranted. For the remainder of the short-term
period, increasing tropical moisture will favor a wetter pattern,
while strengthening ridging aloft will gradually increase mid-level
stability.

For today, moisture will continue to increase as the leading edge of
the broad tropical wave moves through the region. Precipitable water
values will increase from around 1.7-1.8 inches early this morning
to near 2.0 inches by this afternoon, while moisture gradually
deepens through the atmospheric column. Some relatively dry air and
stability in the mid levels could initially limit convection.
Nevertheless, increasing moisture combined with local and diurnal
effects should promote afternoon showers and isolated thunderstorms
across interior and western/northwestern Puerto Rico, with locally
heavy rainfall resulting in ponding of water in roads and poorly
drained areas. There is a low chance of urban and small streams
flooding, mostly over western Puerto Rico.

Deeper moisture will spread across the region tonight into Sunday,
with precipitable water values remaining near or slightly above 2.0
inches and 700-500 mb relative humidity increasing to near or above
normal values. This will favor greater shower coverage, with
locally heavy rainfall and an increasing flooding threat on
Sunday. However, strengthening ridging aloft and decreasing
700-500 mb lapse rates will favor increasing mid-level stability.
At the same time, increasing 850-700 mb lapse rates should
maintain sufficient low-level instability for convective
development. Therefore, convection may become increasingly
shallow, with isolated deeper thunderstorms developing where local
and diurnal effects provide sufficient lifting.

Abundant moisture will persist into Monday, but strengthening
ridging, warming temperatures near 500 mb, and decreasing mid-level
lapse rates should further limit deep convection. Favorable low-
level lapse rates should still support mainly shallow showers, with
isolated deeper convection possible where local effects enhance
convergence, mainly over interior and western Puerto Rico. Streamers
developing downwind of El Yunque into the San Juan metro area and
downwind of the smaller islands cannot be ruled out throughout the
period, potentially enhancing localized heavy rainfall. Training
showers within these streamers may also result in higher rainfall
accumulations over downwind areas. Despite the increasing stability,
the above normal columnar moisture will remain capable of
producing locally heavy rainfall.

Heat will remain a concern through the period as above-normal 925-mb
temperatures and abundant low-level moisture support elevated heat
indices. However, the magnitude of the heat threat on Sunday and
Monday will depend on cloud coverage and the timing of showers, with
increased clouds and earlier convection potentially limiting daytime
heating.

&&

.Long Term(Tuesday through Saturday)...
Issued at 433 AM AST Sat Sep 5 2026

Recent model guidance has trended drier, suggesting limited
prospects for meaningful rainfall relief from the ongoing drought
and water-supply concerns. Ridging north to northwest of the region
should promote generally dry and hot conditions Tuesday. A tropical
wave will then approach as the ridge retreats and a trough develops
east-northeast of the Caribbean, providing the best opportunity for
increased moisture and convection Wednesday into early Thursday.
However, uncertainty remains regarding the timing and depth of the
moisture. A more extensive dry-air mass should follow the wave and
persist through the weekend. Breezy to locally windy east-
southeasterly conditions are also expected as high pressure
strengthens across the North Atlantic.

Extreme heat will likely remain the primary hazard, particularly
Tuesday. Stronger winds, increased cloud cover, and showers may
result in slightly lower temperatures Wednesday and Thursday.
Although below-normal moisture may limit rainfall coverage and
intensity, locally heavy rainfall could produce localized flooding
Wednesday into Thursday, while thunderstorms will pose a lightning
risk. Nevertheless, widespread or substantial rainfall is not
anticipated.

&&

.AVIATION...
(06Z TAFS)
Issued at 433 AM AST Sat Sep 5 2026

Mainly VFR conditions are expected to prevail across all terminals
through the fcst period. Passing -SHRA will continue across the USVI
and eastern PR terminals overnight into the morning hours. Afternoon
convection may result in VCTS and brief MVFR conds at TJBQ after
05/17z, with a PROB30 for -TSRA through 05/21z. Winds light/VRB to
calm overnight, becoming E-ESE at 8-15 kt after 05/13z, with sea
breeze variations and stronger gusts possible near SHRA/TSRA.

&&

.MARINE...
Issued at 433 AM AST Sat Sep 5 2026

Light to moderate east to southeast winds will continue this holiday
weekend, becoming moderate to fresh by Tuesday as surface high
pressure builds across the central Atlantic. These conditions may
result in increasingly choppy seas across regional waters and
Caribbean Passages. A tropical wave will increase shower and
thunderstorm activity across the regional waters late today into
Monday, bringing gusty winds and lightning.

&&

.BEACH FORECAST...
Issued at 433 AM AST Sat Sep 5 2026

The beach forecast remains on track. The latest nearshore buoys
continue to report seas between 1 and 3 feet, with breaking waves
leading to a low risk of rip currents. Although the risk remains low
across all beaches of the islands, beachgoers must pay attention to
the beach conditions a isolated life-threatening rip current often
occur near jetties, piers, reef, and groins. These conditions should
continue this holiday weekend, though strengthening winds should
upgrade the risk by Tuesday, becoming moderate. Therefore, the
moderate risk is expected across northern and eastern-exposed
beaches of the islands on Tuesday, spreading across most beaches
during the second part of next workweek. Beachgoers must exercise
caution, as life-threatening rip currents are possible along the
surf zone. Aside from rip currents, showers and isolated
thunderstorm can be expected each afternoon, moving near coastal
areas of the islands, bringing gusty winds and lightning. Beachgoers
must seek shelter whenever they hear thunder.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001>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...ICP
MARINE/BEACH...MNG

NWS SJU Office Area Forecast Discussion