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545
FXCA62 TJSJ 191703
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
103 PM AST Sun Jul 19 2026

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

.KEY MESSAGES...
Issued at 103 PM AST Sun Jul 19 2026

* Hot conditions will persist through next week, with a limited to
  elevated risk of excessive heat each afternoon. A slight
  increase in moisture on Monday and above-normal temperatures on
  Wednesday could bring the week`s highest heat risk, with
  possible Heat Advisory conditions or worse.

* Another pulse of moderate Saharan dust will spread across the
  islands late tonight through Monday, resulting in hazy skies,
  reduced air quality, and warmer overnight temperatures that may
  increase heat stress.

* Passing showers will increase on Monday as moisture returns,
  followed by a trade wind perturbation on Tuesday that will
  enhance shower coverage and afternoon thunderstorm development.
  Widespread flooding is not expected, but locally heavy
  downpours may cause ponding and isolated urban and small-stream
  flooding.

* Increasing easterly winds will maintain a moderate risk of life-
  threatening rip currents across many beaches of Puerto Rico
  and the U.S. Virgin Islands through early next week. Beachgoers
  should swim near lifeguards, heed local beach warnings, and
  never swim alone.

&&

.Short Term(This evening through Tuesday)...
Issued at 103 PM AST Sun Jul 19 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 15 to 25 mph, with higher gusts at times.
Although skies remained mostly clear across much of the region,
clouds began to develop over the interior and western Puerto Rico
due to orographic and local effects, as well as sea-breeze
convergence. Also, a streamer was observed forming over and
downwind from St Croix.

Although a tropical wave will move well south of the islands, its
trailing moisture will interact with local topography, daytime
heating, and sea breeze convergence, resulting in afternoon
showers across portions of Puerto Rico. A streamer will possibly
develop downwind of the U.S. Virgin Islands, remaining primarily
over the local waters. At the surface, high pressure over the
central Atlantic will maintain breezy easterly trade winds through
the forecast period. Meanwhile, hot conditions will persist
across most urban and coastal areas of Puerto Rico and the U.S.
Virgin Islands, with a limited risk of excessive heat through late
this afternoon.

A Saharan Air Layer (SAL) will spread across the region through
early this week, resulting in hazy skies, reduced air quality, and
warmer overnight temperatures that may increase heat stress. At
the same time, the trailing moisture associated with today`s
tropical wave will move across the area on Monday, increasing low-
level moisture and potentially elevating the risk of excessive
heat from mid-morning through the afternoon due to higher heat
index values. This additional moisture will also support scattered
showers capable of producing moderate to locally heavy rainfall,
particularly where local effects enhance convection. However, a
mid- to upper-level ridge will continue to promote subsidence
aloft and maintain a trade wind inversion, limiting the vertical
extent of convection despite increased moisture.

Model guidance suggests an induced trade wind perturbation will
move across the region on Tuesday. Some solutions, including the
deterministic GFS, indicate moisture deepening to around 600 mb as
the perturbation weakens the trade wind inversion associated with
the mid-level ridge. This feature, combined with daytime heating
and local island effects, will provide the greatest potential for
afternoon thunderstorm development, especially across the interior
and western portions of Puerto Rico. One or two localized,
stronger thunderstorms could produce ponding across poorly drained
areas and isolated urban and small-stream flooding.

&&

.LONG TERM...
Issued at 452 AM AST Sun Jul 19 2026

During the beginning of the long-term period, the primary weather
feature will continue to be an upper-level low inducing a surface
trough northeast of the region. This pattern will weaken the
Atlantic high pressure system, promoting lighter winds across the
islands. The latest guidance suggests that environmental conditions
will be marginally favorable for convective activity. 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
(PWAT) values remaining around 1.7 to 1.9 inches will support a
more favorable environment for shower and thunderstorm
development. 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.

Additionally, on 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. Heat index values will likely reach hazardous levels each
afternoon, especially across urban and coastal locations. A
significant heat risk is currently highlighted for Wednesday. Heat
products will likely need to be issued.

By Thursday and through the remainder of the forecast period,
slightly drier air is expected to filter into the region, with PWAT
values fluctuating between seasonal and below-normal levels,
resulting in more limited shower activity. Winds are forecast to
strengthen once again, becoming breezy to locally windy through the
weekend. The easterly 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 available moisture. The flood risk is expected
to remain low, although a few isolated thunderstorms will remain
possible each afternoon across western Puerto Rico. In terms of
heat, warm to hot conditions are likely to persist most days. An
elevated heat risk is currently in place for Thursday, while a
limited heat risk is expected on Friday. Continue to monitor the
forecast for updates. Residents and visitors are encouraged to
continue practicing heat safety measures to reduce the risk of heat-
related illnesses.

&&

.AVIATION...
(18Z TAFS)
Issued at 103 PM AST Sun Jul 19 2026

Expect VFR conds across all TAF sites. E winds will continue, btwn
15 - 20 kt, gusty winds up to 30 kt, and weakening btwn 5 - 10 kt.
VCSH from time to time across most terminals aft 20/13z.

&&

.MARINE...
Issued at 103 PM AST Sun Jul 19 2026

A surface high pressure over the central Atlantic interacting with
the PanamaColombia Low will maintain moderate to 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 through Monday. Meanwhile, a dense Saharan Air
Layer will move over the region from the east tonight through
tomorrow, Monday, leading to hazy skies, reduced air quality, and
locally reduced visibilities.

&&

.BEACH FORECAST...
Issued at 103 PM AST Sun Jul 19 2026

Increasing easterly trade winds will enhance wave-breaking action
along many beaches of Puerto Rico and the U.S. Virgin Islands
through much of the week, resulting in a moderate risk of life-
threatening rip currents across numerous surf zones. The moderate
risk is expected to persist throughout much of the week for many
north-, east-, and south-facing beaches, although localized day-
to-day variations are possible. Beachgoers should swim near
lifeguards whenever possible, heed beach warning flags, and never
swim alone.

A limited-to-local elevated risk of excessive heat is also
expected at many local beaches through the first half of the week,
particularly during the late morning and afternoon hours. Stay
well hydrated, take frequent breaks in the shade, and use
sunscreen to reduce the risk of heat-related illnesses.

&&

.FIRE WEATHER...
Issued at 103 PM AST Sun Jul 19 2026

A Fire Danger Statement (RFD) remains in effect for the local fire
weather zones. Observations continue to support RFD conditions
across the southern half of PR and the USVI. At the same time,
critically dry fuels and persistent soil moisture deficits persist
across portions of the islands, with KBDI values remaining above
critical thresholds. Multiple fire incidents have already been
reported across PR today, underscoring the elevated fire danger.
Combined with breezy trade winds, any new fires that develop could
spread rapidly through dry vegetation, particularly across PR`s
southern coastal plains. Residents and visitors are urged to avoid
outdoor burning and exercise extreme caution with open flames,
discarded cigarettes, or any activity capable of producing sparks.

&&

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

$$

MORNING SHIFT...CAM/MMC
EVENING SHIFT...ICP/MRR

NWS SJU Office Area Forecast Discussion