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628
FXCA62 TJSJ 181858
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
258 PM AST Sat Jul 18 2026

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

.KEY MESSAGES...
Issued at 245 PM AST Sat Jul 18 2026

* Hot conditions will persist through much of next week. Elevated
  heat indices are expected across urban and coastal areas each
  afternoon, with Heat Advisory conditions possible in some
  locations through the weekend.

* Passing showers will continue to move across the region each
  day, with isolated afternoon showers and thunderstorms
  developing over western Puerto Rico. Widespread flooding is not
  expected, though brief ponding may occur during the heaviest
  showers.

* The breezy easterly winds will persist across most of the
  region through early next week.

* A Saharan Air Layer will bring moderate concentrations
  spreading across the islands from late Sunday night into Monday,
  resulting in hazy skies, reduced air quality, and limited
  visibility. The associated dry and warm air mass may also
  contribute to warmer overnight temperatures and an increased
  heat risk.

&&

.Short Term(This evening through Monday)...
Issued at 245 PM AST Sat Jul 18 2026

Local weather stations across the islands reported maximum
temperatures in the 90s at most urban and coastal locations. Peak
heat index values ranged from 100F to 107F. Winds were generally
from the east at 10 to 20 mph, with higher gusts at times.
Although skies remained mostly clear across much of the region,
clouds are beginning to develop over western Puerto Rico due to
local effects and sea breeze convergence.

A mid-level ridge will remain the dominant weather feature across
the region, promoting dry air aloft and strong subsidence over
the northeastern Caribbean. As a result, a relatively stable
weather pattern is expected to persist through the short-term
forecast period. At the surface, high pressure over the central
Atlantic interacting with the PanamaColombia Low will maintain a
tight local pressure gradient, resulting in breezy conditions.
These winds will continue to transport patches of low-level
moisture across the region from time to time, leading to a few
passing showers over windward areas.

At the surface, high pressure over the central Atlantic will keep
a tropical wave well south of Puerto Rico and the U.S. Virgin
Islands as it moves westward across the southern Caribbean Sea.
Meanwhile, a dense Saharan Air Layer will overspread the region
from late Sunday night into Monday, bringing moderate
concentrations of Saharan dust, reduced air quality, hazy skies,
and locally reduced visibilities. The associated warm and dry air
mass will also contribute to warmer-than-normal overnight
temperatures. Saharan dust concentrations are expected to peak on
Monday across the islands.

&&

.LONG TERM...
Issued at 442 AM AST Sat Jul 18 2026

By Tuesday, Saharan dust concentrations are expected to decrease to
low levels. At the same time, the latest guidance suggests that
environmental conditions will become more favorable for convective
activity due to the influence of a series of upper-level lows and
troughs. Winds will become lighter from the east-northeast. At 500
mb, temperatures are forecast to cool from above-normal values to
near seasonal levels, around -6C to -7C. In addition, lower 250 mb
heights, near-seasonal mid-level relative humidity, and precipitable
water values increasing to around 1.7 to 1.9 inches will support a
more favorable environment for shower and thunderstorm development.

As a result, Tuesday is expected to have the highest rain chances of
the long-term forecast period, particularly during the afternoon
hours. A limited flood risk is highlighted across west-central and
western Puerto Rico due to the potential for ponding of water on
roads and in poorly drained areas, along with a low chance of urban
and small-stream flooding.

By Wednesday, afternoon convection is also expected to develop
across the northwestern quadrant of Puerto Rico as winds gradually
veer to a more southeasterly direction. Another primary concern for
Tuesday and Wednesday will be the heat risk. With the increase in
available moisture, conditions are expected to become and feel
warmer. An elevated heat risk is forecast for Tuesday. By Wednesday,
the combination of light southeasterly flow, seasonal moisture, and
925 mb temperatures around two standard deviations above normal is
expected to result in the warmest day of the week, with probably
elevated or significant heat risk. High temperatures are forecast to
reach the lower to middle 90s across coastal and urban areas during
the early afternoon hours. Heat index values will likely reach
hazardous levels each afternoon, especially across urban and coastal
locations. Heat products will likely be needed on both days.
Residents and visitors are encouraged to continue practicing heat
safety measures to reduce the risk of heat-related illnesses.

Drier air is expected to filter into the region on Thursday, with
PWAT values briefly decreasing into below normal values, resulting
in more limited shower activity. Winds are forecast to strengthen
once again, becoming breezy to locally windy through the weekend.
From Friday into Saturday, the steering flow will continue to favor
passing showers across windward areas during the nighttime and
morning hours, followed by afternoon showers over western Puerto
Rico driven by local effects and seasonal precipitable water values.
A limited heat risk is expected to persist through the end of the
week.

&&

.AVIATION...
(18Z TAFS)
Issued at 245 PM AST Sat Jul 18 2026

VFR conds across all TAF sites throughout the fcst prd. Easterly
winds will continue, btwn 15 - 20 kt, gusty winds up to 30 kt, and
weakening btwn 6 - 12 kt and becoming VRB aft 18/23z. VCSH from time
to time across most terminals aft 19/13z.

&&

.MARINE...
Issued at 245 PM AST Sat Jul 18 2026

A surface high pressure over the central Atlantic interacting with
the PanamaColombia Low will maintain moderate to locally fresh
easterly winds and moderate to locally choppy seas through much of
the forecast period. A tropical wave will remain well south of
Puerto Rico and the U.S. Virgin Islands as it moves westward
across the southern Caribbean from late Sunday into Monday,
resulting in little direct impact to the local waters. Meanwhile,
a dense Saharan Air Layer will overspread the region from late
Sunday night through Monday, leading to hazy skies, reduced air
quality, and locally reduced visibilities, although marine
visibilities are expected to remain above 5 nautical miles.

&&

.BEACH FORECAST...
Issued at 245 PM AST Sat Jul 18 2026

Increasing winds will enhance wave-breaking action along much of
the coastline of Puerto Rico and the U.S. Virgin Islands,
resulting in a moderate risk of life-threatening rip currents
across most surf zones. This moderate risk is expected to persist
through at least Monday at many local beaches. Beachgoers should
swim near lifeguards whenever possible, heed beach warning flags,
and never swim alone.

A limited to elevated risk of excessive heat is also expected at
many local beaches today through the first half of the week. Stay
well hydrated, seek shade whenever possible, and use sunscreen to
reduce the risk of heat-related illness.

&&

.FIRE WEATHER...
Issued at 245 PM AST Sat Jul 18 2026

A Fire Danger Statement (RFD) remains in effect for the local fire
weather zones. Critically dry fuels and significant soil moisture
deficits persist across portions of most PR and the USVI, with
KBDI values remaining above critical thresholds. Any fires that
develop could spread through dry vegetation, particularly across
the southern coastal plains. Residents and visitors should avoid
outdoor burning and exercise caution when using open flames or
other potential ignition sources.

&&

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

$$

MORNING CREW...CAM/MMC
EVENING CREW...MMR/YZR

NWS SJU Office Area Forecast Discussion