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105
FXCA62 TJSJ 241602
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1202 PM AST Thu Sep 24 2026

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

.KEY MESSAGES...
Issued at 1200 PM AST Thu Sep 24 2026

- Showers and thunderstorms will continue this afternoon
  increasing the chance of urban and small stream flooding. The
  U.S. Virgin Islands will see passing showers.

- Moisture content will decrease across the local area by the end
  of the week, decreasing showers and thunderstorm coverage, but
  scattered afternoon showers are still expected due to local
  effects.

- The heat risk will likely increase to elevated levels by the
  weekend, stay hydrated.

- A moderate risk of rip currents is expected to continue along
  northern and eastern beaches of Puerto Rico and northern U.S.
  Virgin Islands through at least Saturday, then potentially
  increasing to high on Sunday into early next week.

&&

.Short Term(This afternoon through Saturday)...
Issued at 1200 PM AST Thu Sep 24 2026

Early this morning, showers and isolated thunderstorms were observed
across the regional waters as a surface perturbation continued
moving westward. However, coverage and intensity gradually decreased
through the morning. Meanwhile, heat index values were already
exceeding 100 degrees by late morning across several urban and
coastal areas, particularly across north-central and western Puerto
Rico. Above-normal temperatures and sufficient low-level moisture
will maintain a limited heat threat this afternoon, although
conditions should generally remain below Heat Advisory criteria
except in localized urbanized areas.

A tropical upper-tropospheric trough (TUTT) will remain near the
forecast area through the short-term period. Although the islands
will remain beneath a relatively unfavorable portion of the TUTT,
sufficiently cold mid-level temperatures, around -7 to -8 degrees
Celsius at 500 mb, will maintain steep 700-500 mb lapse rates and
adequate instability. For this afternoon, ample low- to mid-level
moisture, sea-breeze convergence, and intense surface heating will
provide sufficient forcing to support another active convective
period. Additionally, the atmospheric column has moistened compared
to yesterday, with the 24/12Z TJSJ sounding measuring a PWAT value
of 2.18 inches, above the 90th percentile of the climatological
distribution. Therefore, convective activity could initiate somewhat
earlier than yesterday. Supporting this trend, by 24/15Z, very
localized showers had already developed in the vicinity of Ponce,
while a streamer downwind of El Yunque was producing moderate to
heavy showers and isolated thunderstorms.

Showers and thunderstorms are expected to further develop this
afternoon across the interior and western to northwestern portions
of Puerto Rico, where saturated soils and elevated streamflows could
enhance the flooding and landslide threat. Periods of heavy rainfall
could result in ponding of water on roads and in poorly drained
areas, as well as urban and small-stream flooding. Localized flash
flooding cannot be ruled out where the heaviest rainfall persists.
Additional streamers may also develop downwind of the smaller
islands and El Yunque, potentially affecting the San Juan
metropolitan area. The strongest thunderstorms could also produce
frequent lightning and gusty winds.

For Friday and Saturday, dynamics aloft will change little, but
moisture availability will become the main limiting factor.
Precipitable water values are expected to decrease to near or
slightly below normal, favoring generally fair conditions during the
morning with a few passing showers over windward areas, followed by
more localized and shorter-lived afternoon convection across
interior and western Puerto Rico. This should reduce the overall
flooding threat.

Heat concerns will persist through the period. Model guidance
indicates gradually increasing 925 mb temperatures into Saturday,
while trace amounts of Saharan dust and somewhat lower cloud
coverage could further enhance daytime heating. Therefore, Heat
Advisories cannot be ruled out, particularly on Saturday.

&&

.Long Term(Sunday through Thursday)...
Issued at 117 AM AST Thu Sep 24 2026

The weather conditions over the long term period will continue to be
influenced by several synoptic features. Over the eastern Atlantic
ocean a low level high pressure system will promote an ENE wind
flow. The conditions are expected to become breezy to locally windy
across the US Virgin Islands and Puerto Rico from Monday into mid-
week. Additionally, a lingering upper-level low pressure system
located to the east of the CWA will continue to drive upper-level
convergence through mid-to-late next week. This will act to limit
the potential for the development of deep convection over the
region. On the other hand, while a tropical wave is expected to
reach the forecast region between Monday and Tuesday the moisture
field associated with the system will remain to the north and south
of the US Virgin Islands and Puerto Rico with lower than average
precipitable water (PWAT) values intruding the region. Nonetheless,
on Monday the atmospheric column is expected to be moister than most
of the days in the long term period. Coupled with local effects, the
day is expected to be favorable for the development of isolated
shower and thunderstorm activity.

Given that the synoptic features are currently acting to limit
weather activity, the day-to-day is expected to be driven primarily
by local effects with seasonal conditions dominating the observed
weather pattern through late next week. With rainfall activity
expected over the US Virgin Islands and eastern Puerto Rico in the
morning and over the interior and northwestern Puerto Rico during
the afternoon. Weather conditions will become more favorable by
Thursday, with a more humid vertical profile returning. Mid-
tropospheric temperatures are also forecasted to be below -6 degrees
Celsius, increasing the potential for the development of deep
convective cells. Risks associated to extreme heat continue to be
one of the main concerns throughout the rest of the forecast period
with 925 mb temperatures expected to be 2 standard deviations above
normal ranges for the season into early next week. As individuals
prepare for the weekend it is recommended to adjust outside
activities and events accordingly and to remain hydrated. Citizens
ands visitors are invited to stay alert of the evolving weather
conditions as we move into the weekend.

&&

.AVIATION...
(18Z TAFS)
Issued at 1200 PM AST Thu Sep 24 2026

SHRA/TSRA will affect mainly TJSJ, TJPS, and TJBQ this aftn, with
brief MVFR/IFR conds from reduced VIS/CIGs and possible mtn
obscurations. Activity should diminish after 24/22Z, though VCSH
will persist overnight at TJSJ/TIST/TISX. Another round of SHRA/TSRA
is expected aft 25/17Z, mainly affecting TJBQ. Winds ESE-SE 10-15 kt
with sea breeze variations and occasional hir gusts, becoming
light/VRB overnight.

&&

.MARINE...
Issued at 1200 PM AST Thu Sep 24 2026

Gentle to moderate east-to-southeast winds are expected through
most of the forecast period. Seas around 2 to 4 feet will persist
through at least Saturday, while pulses of a weak long-period
northeasterly swell continue to spread across Atlantic waters and
local Caribbean passages. Another long-period northerly swell is
expected to spread across the Atlantic waters around Sunday into
early next week, with seas building around 4 to 5 feet across
Atlantic-exposed areas.

Additionally, afternoon showers and isolated thunderstorms are
possible each day, particularly across western waters of Puerto
Rico, bringing the potential for locally strong wind gusts,
frequent lightning, and brief reductions in visibility.

&&

.BEACH FORECAST...
Issued at 1200 PM AST Thu Sep 24 2026

A moderate risk of rip currents is forecast to continue along the
northern and eastern beaches of Puerto Rico and the northern U.S.
Virgin Islands through at least next Saturday. By Sunday and into
early next week, a long-period northerly swell is expected to
spread across the Atlantic waters, potentially increasing the rip
current risk to high levels, with life-threatening rip currents
likely in the surf zones. Beachgoers will be urged to exercise
caution and heed the advice of lifeguards, beach patrol flags, and
warning signs.

Another beach hazard will be the heat threat, particularly during
the upcoming weekend. Additionally, afternoon showers and
thunderstorms will be possible each day, especially across the
western beaches of Puerto Rico. If thunder is heard, seek shelter
immediately.

&&

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

$$

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

NWS SJU Office Area Forecast Discussion