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916
FXCA62 TJSJ 290549
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
149 AM AST Tue Sep 29 2026

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

.KEY MESSAGES...
Issued at 133 AM AST Tue Sep 29 2026

- Limited heat risk for the next few days, as easterly trade winds
  strengthen, allowing only localized areas across Puerto Rico and
  the US Virgin Islands to experience brief periods near heat
  advisory criteria.

- The US Virgin Islands and Puerto Rico should experience clear
  skies through the first half of the day, followed by showers and
  thunderstorms during the afternoon hours each day. Therefore, a
  limited flooding risk should prevail over western PR,
  increasing to elevated by the end of the workweek.

- Moderate rip current risk for western, northern, and eastern PR,
  as well as, the US Virgin Islands, while the rest should
  experience low risk. Regardless, people are urge to exercise
  caution and always swim near a lifeguard.

&&

.Short Term(Today through Thursday)...
Issued at 133 AM AST Tue Sep 29 2026

Like previous nights, generally calm weather conditions prevailed
across the islands, with only a few passing showers over the
waters. Mostly clear skies allowed temperatures to fall into the
70s across urban and coastal areas, while observations across the
higher elevations dropped into the upper 60s to low 70s. Winds
remained light and variable.

Overall, slightly drier conditions are expected through much of the
short-term period as surface to mid-level high pressure remains
the primary feature across the region, despite a weak upper-level
trough lingering nearby. Limited moisture and weak forcing should
keep precipitation chances relatively low through Wednesday.
Current satellite imagery shows mostly clear skies across the
islands, with only a few pockets of showers over the waters and
occasionally moving into eastern Puerto Rico and the U.S. Virgin
Islands. Generally sunny to partly cloudy skies are expected,
along with gradually increasing winds through midweek. This
pattern should provide favorable conditions for outdoor work and
recreational activities, particularly during the morning and early
afternoon hours. However, diurnal heating and local effects
should still promote typical afternoon convection across western
Puerto Rico, where a limited flooding risk will persist each
afternoon. Regarding heat, a break from heat products is
anticipated, as only localized areas are expected to briefly
experience heat indices near advisory criteria. Nevertheless,
those spending extended periods outdoors should continue to stay
hydrated and take appropriate breaks, especially during the
warmest part of the day.

Conditions will begin to transition late Thursday as an upper-
level trough and surface disturbance approach the region, allowing
moisture to gradually increase. The first half of Thursday should
remain generally favorable for outdoor activities, with increasing
cloud cover and shower activity becoming more likely later in the
day as moisture increases. This will mark the beginning of a
slightly wetter pattern extending beyond the short-term period.
Those with plans late Thursday and beyond should continue to
monitor forecast updates as the potential for showers and
associated impacts increases.

&&

.Long Term(Friday through Tuesday)...
Issued at 133 AM AST Tue Sep 29 2026

Unstable conditions are still expected on Friday and Saturday,
transitioning to a typical weather pattern Sunday onward. Model
guidance continues to suggest a surface high pressure the western
Atlantic, promoting an E-SE wind flow throughout the period. As
mentioned in the previous discussion, a surface trough may weaken
the surface high, with isolated breezy conditions across coastal
areas of the islands. Friday and Saturday remain the active days of
the long-term, as the latest model guidance suggests that the
presence of upper-level troughs should introduce instability across
the eastern Caribbean. In terms of moisture, the deterministic
guidance of the GFS and ECMWF continues to suggest abundant tropical
moisture across the region, with PWAT values between 1.8 and 2.0
inches, mainly in the low and mid levels. Additionally, model
sounding plots continue to show skinny profiles, with weak inversion
caps that could easily be broken and high CAPEs.  Due to the
proximity of the troughs, mid-levels might get cooler than expected
(500 mb temperatures reaching -8 C) with steeper lapse rates in the
mid-levels, allowing cloud growth and instability aloft. Therefore,
the most likely scenario should be for isolated to scattered showers
across the windward sections during the night and morning hours,
with deep convection in the afternoon, particularly across the
interior and western/northwestern. Additionally, local island
streamers are also expected, affecting the San Juan Metro Area. On
Sunday, drier air is expected to filter in the low-to-mid-levels
(850 - 500mb), inhibiting deeper convection over the islands, as
precipitable water (PWAT) values are expected to drop to seasonal or
below-seasonal values. However,  local effects and daytime heating
driven by an easterly flow should promote afternoon convection
mainly over the interior to western half of Puerto Rico. A similar
pattern is expected on Monday, as drier air persists in the low-to-
mid levels. In general, shower and thunderstorm activity is expected
each day, with the highest flooding threat on Friday and Saturday.
Rainfall accumulations could enhance the chance of urban and small
stream flooding over the aforementioned areas. Meanwhile, Sunday and
Monday rainfall activity may lead to ponding of water over roadways
and poorly drained areas, including minor flooding. In addition to
flooding, thunderstorm activity could produce gusty winds and
frequent lightning, without ruling out small hail.

Warmer conditions are expected throughout the long term, with
seasonal to above-seasonal 925-mb temperatures. Although heat
indices should exceed 100 F, a limited risk of excessive heat will
persist throughout the forecast period. Individuals sensitive to
these conditions should stay hydrated and avoid prolonged outdoor
activities.

&&

.AVIATION...
(06Z TAFS)
Issued at 133 AM AST Tue Sep 29 2026

VFR conditions will prevail across all terminals. However,
passing SHRA and VCTS may cause tempo and brief MVFR conds at
TJPS/TJBQ from 29/17Z thru 29/21z. Elsewhere, mostly VCSH
expected. Increasing winds from the ENE at 12-16 kt with higher
gusts aft 29/13z.

&&

.MARINE...
Issued at 133 AM AST Tue Sep 29 2026

A small northerly swell will continue to gradually subside today
while moderate easterly trade winds persist. Choppy conditions are
expected across the Atlantic waters and Mona Passage, with winds
strengthening tonight into Wednesday and becoming locally fresh.
Seas will generally range from 3 to 5 feet, occasionally up to 6
feet across the Atlantic waters and passages. Periods of showers
will continue, with afternoon showers and isolated thunderstorms
developing mainly near western and northern Puerto Rico.
Thunderstorms may produce locally higher winds and seas,
lightning, and reduced visibility.

&&

.BEACH FORECAST...
Issued at 133 AM AST Tue Sep 29 2026

Beach conditions will improve today as the northerly swell gradually
subsides. However, a moderate risk of rip currents will persist
along the exposed beaches of northern and eastern Puerto Rico, as
well as Culebra and the U.S. Virgin Islands. Breaking waves of
around 5 feet are expected along portions of the northern coastline,
with lower heights elsewhere. Afternoon showers and isolated
thunderstorms may also pose a lightning threat to beachgoers,
particularly across western and northern Puerto Rico.

&&

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

$$

SHORT TERM/AVIATION...MMC
LONG TERM...MNG/JCP
MARINE/BEACH FORECAST...ICP

NWS SJU Office Area Forecast Discussion