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748
FXCA62 TJSJ 301841
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
241 PM AST Thu Jul 30 2026

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

.KEY MESSAGES...
Issued at 240 PM AST Thu Jul 30 2026

- Increasing moisture on Friday and another tropical wave arriving
  Saturday afternoon will bring a higher chance of showers and
  thunderstorms through Sunday, increasing the potential for
  localized flooding, lightning, gusty winds, and reduced
  visibility, which could impact outdoor activities.

- Strengthening easterly winds will continue to build seas and
  create hazardous marine and beach conditions through the week,
  resulting in choppy seas.

- Hot conditions will return on Sunday across Puerto Rico and the
  U.S. Virgin Islands, increasing the risk of heat-related
  illnesses, especially for vulnerable populations, outdoor
  workers, and anyone spending extended periods outside.

&&

.Short Term(This evening through Saturday)...
Issued at 240 PM AST Thu Jul 30 2026

Hazy skies persisted today due to moderate concentrations of
Saharan dust, mostly fair weather conditions prevailed across
Puerto Rico. Around noon, scattered showers due to a streamer
developed near the El Yunque area, where radar estimates indicated
around 0.40 inches of rainfall. Daytime high temperatures ranged
from the upper 80s to the low 90s, with heat indices reaching
between 108 and 113F across north-central, western, and southern
Puerto Rico. An Extreme Heat Warning remains in effect through 5
PM this afternoon. Meanwhile, easterly winds generally ranged
between 15 and 20 mph, with occasional gusts of 23 to 30 mph.

For the remainder of the afternoon, isolated to scattered showers
driven by daytime heating, sea breeze convergence, and local
effects are expected to develop across western Puerto Rico.
Activity should remain limited and localized, with no significant
flooding concerns, as a dry mid-level layer and extensive high
cloud cover associated with an upper-level low suppress rain
development.

Moderate concentrations of Saharan dust will persist through
tonight before gradually decreasing Friday morning. Although dust
concentrations will be less, low concentrations will still remain
present. At the same time, a wind perturbation is expected to
increase low-level moisture. Based on the latest guidance,
precipitable water (PWAT) values are forecast to increase from
around 1.5 inches (below normal, 25th percentile) to between 1.75
and 1.80 inches (near seasonal values, around the 50th percentile).
This will slightly increase the potential for and frequency of
passing showers across windward areas, as well as the coverage of
afternoon convection across western Puerto Rico, where isolated
thunderstorms will be possible. A limited flood risk is being
highlighted for northeastern and metropolitan Puerto Rico due to
the potential for El Yunque streamer formation, as well as across
western sectors where afternoon convection is expected on Friday.

By late Saturday morning onward, moisture associated with a
tropical wave is expected to arrive, accompanied by lighter
southeasterly winds. PWAT values are projected to increase to
seasonal or above-normal levels, with additional moisture
extending into the mid and upper levels, according to the latest
GFS cross-section analysis. The 500-mb temperature is forecast to
cool to around -7C, increasing the potential for thunderstorm
development. However, the development and intensity of rainfall
will also depend on how much upper-level cloud cover develops.
Continue to monitor the forecast as updates become available and
forecast uncertainty decreases.

For the remainder of the short-term forecast period, a limited or
elevated heat risk will likely persist. Residents and visitors
are encouraged to stay hydrated and continue practicing heat
safety measures.

&&

.Long Term(Sunday through Thursday)...
Issued at 340 AM AST Thu Jul 30 2026

Variable conditions should continue in the long-term forecast, with
the best chance of precipitation early next week. As mentioned in
previous discussions, a broad surface high pressure lingering over
the central Atlantic should mainly maintain an ESE-SE wind flow,
with locally breezy conditions. The latest global model solutions
suggest lingering moisture associated with a tropical wave and an
upper-level low located over Hispaniola. Based on the
deterministic guidance of the GFS and ECMWF, PWAT values should
remain between 1.8 and 2.0 inches, with localized areas reaching
2.2 inches, slightly above climatological normal.

Looking at the cross-section, low-level moisture content should
remain seasonal to above-normal (60-80%), while mid-level moisture
content may reach two standard deviations above normal (up to
80%). In terms of instability, the proximity of the upper-level
low should maintain cool mid-level temperatures (500 mb
temperatures around -6 and -7 degrees Celsius), with the best
vorticity and divergence east of the CWA, which should allow cloud
growth and deeper convection. Additionally, the Galvez-Davison
Index (GDI) suggests the potential of isolated to scattered
thunderstorms moving across the local islands during Sunday
morning. These conditions may lead to an advective pattern during
the morning hours, with afternoon convection over portions of
western/northwestern Puerto Rico, including local islands
streamers. Rainfall accumulations could result in ponding of
water over roadways and poorly drained areas, including localized
urban and small stream flooding.

As the upper-level low migrates northwest, the latest guidance
suggests a drier air mass filtering into the region, with low- to
mid-level RH plummeting to below climatological values (between 20
and 40%). Additionally, the NASA GEOS Dust Extinction suggests a
dense plume of Saharan dust moving across the region on Monday
morning, likely to bring hazy skies, reduced visibility, and
deteriorating air quality. Although the combination of daytime
heating, local effects, and available moisture may lead to
afternoon convection over western Puerto Rico, shower activity may
become short-lived with low rainfall accumulations. A similar
pattern is likely on Tuesday, while shower activity should
increase once again on Wednesday, as a trough approaches the CWA.

Under an ESE-SE wind flow, warmer to hotter temperatures can be
expected across the CWA, particularly over urban and low-lying
areas. With periods of high moisture content and the influence of
Saharan dust, maximum temperatures should remain in the low 90s,
while heat indices will likely exceed 100 degrees Fahrenheit.
Therefore, the heat threat will remain elevated throughout the
forecast period.

&&

.AVIATION...
(18Z TAFS)
Issued at 240 PM AST Thu Jul 30 2026

Mainly VFR conditions are expected during this forecast period.
TJBQ may observe -RA/VCSH thru 30/20-21Z. The presence of low to
moderate concentrations of Saharan dust will maintain slight
reductions in visibility and hazy skies. from this afternoon into
the coming days. Another aviation concern will be the winds, with
gusts near 30 kts expected today thru 30/23Z, then around 10 kts
overnight. Winds increasing again after 31/13-14Z.

&&

.MARINE...
Issued at 240 PM AST Thu Jul 30 2026

The surface high pressure over the central Atlantic will continue
to build and strengthen through early next week. This will
promote moderate to fresh trades for the next few days. These
conditions will maintain choppy seas across the regional waters
and passages through at least Saturday. Moderate concentrations of
Saharan dust will continue to cause hazy skies and slightly
reduced visibilities through early Friday.

&&

.BEACH FORECAST...
Issued at 240 PM AST Thu Jul 30 2026

Breezy conditions will support a moderate risk of rip currents
across most of the east, north, and southern beaches of Puerto
Rico, and the U.S. Virgin Islands through Saturday. The risk is
expected to drop along the southern beaches of Puerto Rico,
Vieques, Culebra, and the USVI by Sunday. Nevertheless, beachgoers
should be aware that life-threatening rip currents often occur in
the vicinity of groins, jetties, reefs, and piers. Hazy
conditions will continue through tonight across all the islands
due to Saharan dust.

&&

.FIRE WEATHER...
Issued at 240 PM AST Thu Jul 30 2026

Based on surface observations, minimum relative humidity values
have been near or above critical thresholds today. Similar
conditions are expected tomorrow. Critically dry fuels persist
across southern Puerto Rico and St. Croix, with Keetch-Byram
Drought Index (KBDI) values remaining well above the critical
threshold. East winds are expected to remain above or near the
critical levels through at least tomorrow, slightly which could
promote the rapid spread of any fire that develops.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning until 5 PM AST this afternoon for
     PRZ001>005-007-008-010>013.

VI...Extreme Heat Warning until 5 PM AST this afternoon for VIZ001-
     002.

AM...None.
&&

$$

SHORT TERM/AVIATION/FIRE...YZR
LONG TERM...MNG
MARINE/BEACH...MMC

NWS SJU Office Area Forecast Discussion