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625
FXCA62 TJSJ 290705
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
305 AM AST Mon Jun 29 2026

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

.KEY MESSAGES...
Issued at 257 AM AST Mon Jun 29 2026

* A passing tropical wave will result in shower and thunderstorm
  activity today, resulting in ponding of water over roadways and
  poorly drained areas, including urban and small stream
  flooding, across the islands.

* Warmer to hot conditions are expected for the next few days, with
  heat indices exceeding 100 degrees Fahrenheit across urban and low-
  lying areas of Puerto Rico and the U.S. Virgin Islands. Stay
  hydrated.

* Moderate to high concentrations of Saharan Dust will likely
  return by Tuesday morning, resulting in hazy skies, reduced
  visibility, and poor air quality. Sensitive groups must follow
  medical recommendations.

&&

.Short Term(Today through Wednesday)...
Issued at 257 AM AST Mon Jun 29 2026

Abundant moisture associated with a tropical wave moving over the
region resulted in moderate to heavy rainfall across portions of
eastern and northeastern Puerto Rico, Culebra, Vieques, and the U.S.
Virgin Islands during the overnight hours. Doppler radar estimated
rainfall accumulations of up to 1.0 inch over the municipalities of
Humacao, Juncos, and Las Piedras. The strongest thunderstorms with
frequent lightning remained mostly over the Anegada Passage,
particularly between St. Croix and Vieques. Overnight lows across
the region ranged from the upper 70s to low 80s in urban and coastal
areas, and from the upper 60s to low 70s in the mountains.

Showers and isolated thunderstorms will continue to move across the
local waters, the U.S. Virgin Islands, and eastern Puerto Rico
during the morning hours. This will likely result in the ponding of
water in low-drainage areas. As the wave continues to move across
the region, it will maintain an influx of abundant moisture over the
islands. This moisture, combined with daytime heating and local
effects, will trigger afternoon convective activity across
northwestern Puerto Rico. Heavy rainfall and isolated thunderstorms
are expected across these areas, resulting in an elevated risk of
flooding. Potential impacts include ponding of water on roadways,
urban and small-stream flooding, and localized flash flooding. Gusty
winds will also be possible within the heavier shower activity.

Later tonight, the wave axis will continue to move westward toward
the Dominican Republic. Following the passage of the wave, drier air
will begin to filter back into the region along with moderate to
high concentrations of Saharan dust. This will result in hazy skies,
reduced visibilities, and poor air quality through the end of the
workweek. Sensitive groups, including individuals with respiratory
conditions, are urged to limit prolonged outdoor exposure and take
necessary precautions. Simultaneously, a broad surface high-pressure
system centered over the central Atlantic and a mid-level ridge
settling over the northeastern Caribbean will promote drier, stable
conditions aloft, limiting widespread shower formation through the
rest of the period. However, occasional patches of moisture embedded
in the trade winds will still bring brief showers to the area,
though no significant accumulations are expected as stable
conditions prevail.

Under this weather scenario, temperatures will rise into the upper
80s to low 90s across coastal and urban areas, and into the low to
mid-80s in the mountains. Heat indices across the region are
forecast to reach or surpass 100F, particularly during the peak
heating hours of the day. Residents and visitors are urged to
practice heat safety by staying hydrated, limiting strenuous outdoor
activities, and taking frequent breaks in shaded or air-conditioned
areas.

&&

.Long Term(Thursday through Monday)...
Issued at 257 AM AST Mon Jun 29 2026

For the long-term forecast period, the region will experience a
transition from a marginally unstable environment to a drier, hazier
pattern before moisture returns early next week on Monday. At the
surface, a dominant high-pressure system will maintain a generally
easterly low-level wind flow, which is expected to veer to the
southeast by Thursday morning. Aloft, a 250 mb cut-off low will
linger near the local area from Thursday into Friday, providing
modest upper-level support and atmospheric instability, with 500 mb
temperatures forecast to hover between -8 C and -7 C during this
time. On the other hand, precipitable water values are expected to
range between 1.4 and 1.6 inches.  Given the expected conditions,
passing showers are anticipated across eastern sections of Puerto
Rico during the morning hours, followed by the development of
afternoon showers over the western interior and northwestern
quadrants of the island, fueled by local effects and daytime heating.

From Friday through Sunday, a slightly drier weather pattern will
establish across the forecast area. Available moisture will become
relatively shallow, generally trapped between the 1000 and 850 mb
levels. Furthermore, recent NASA Goddard aerosol model guidance
indicates the arrival of another mass of Saharan particulates. This
dust will result in hazy skies, leading to mostly dry and variable
conditions with very limited rainfall accumulations throughout the
weekend. By Monday, a more uniform area of low-level moisture is
forecast to filter into the region. This will aid in diminishing the
hazy conditions as dust concentrations decrease, promoting a return
to a more typical, scattered shower pattern across the islands.

Regardless of the fluctuations in moisture and Saharan dust,
persistently warm to hot conditions will dominate the entirety of
the long-term period. An elevated heat threat is expected each day,
particularly across urban and coastal areas. Maximum heat index
values will consistently peak between 100 and 108 F across portions
of the north-central coastal plain and southern sectors of Puerto
Rico during the peak daytime heating hours.

&&

.AVIATION...
(06Z TAFS)
Issued at 257 AM AST Mon Jun 29 2026

Mainly VFR conds are expected to prevail across most terminals
today. However, a tropical wave will continue to move across the
region today, promoting the development of SHRA and iso TSTMs,
this will result in VCSH/VCTS across most terminals thru 29/23z.
Mtn tops obscd and BKN cigs near FL030 are expected with the wave
passage. SE winds between 12-16 kt are expected with higher gusts
and sea breeze variations. Winds will become light and variable
at 5-10 kt aft 29/23z.

&&

.MARINE...
Issued at 257 AM AST Mon Jun 29 2026

A tropical wave will move across the US Virgin Islands and Puerto
Rico, bringing gusty winds and lightning, creating localized
hazardous conditions for small craft through at least this evening.
Trailing the tropical wave, a dense Saharan Air Layer will
deteriorate air quality on Tuesday and Wednesday. The surface high
pressure across the Central Atlantic will promote the return of
moderate to locally fresh east to east-southeasterly winds causing
moderate chops or even choppy seas.

&&

.BEACH FORECAST...
Issued at 257 AM AST Mon Jun 29 2026

Most beaches along the east, south, and west coasts of Puerto Rico,
as well as those in Culebra, Vieques, St. John, and St. Thomas, have
a low risk of rip currents. However, beaches in St. Croix and
northern Puerto Rico face a moderate risk of rip currents, which can
be life-threatening. It`s important to note that even at low-risk
beaches, isolated, life-threatening rip currents can still occur,
particularly near jetties, groins, reefs, and piers. This will
prevail through at least the middle of the week.

In addition, a tropical wave will bring thunderstorms across Puerto
Rico and the US Virgin Islands today. If you are at the beach or
participating in outdoor activities, remain alert for lightning.
Remember: If you can hear thunder, you are close enough to be struck
by lightning. Move to a substantial building or a hard-top vehicle
immediately and remain there until 30 minutes after the last rumble
of thunder.

From Tuesday onward, expect hot, humid conditions that may produce
dangerous heat levels at the beaches. Stay hydrated, seek shade
frequently, wear lightweight clothing, and limit prolonged sun
exposure during the hottest part of the day.

&&

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

$$

SHORT TERM...GRS
LONG TERM....LIS
MARINE & BEACH FORECAST...CAM

NWS SJU Office Area Forecast Discussion