National Weather Service Today's Weather Impact Levels

793
FXCA62 TJSJ 080907
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
507 AM AST Fri Aug 8 2025

.KEY MESSAGES...

* Another warm day is expected across the U.S. Virgin Islands and
  Puerto Rico with highs reaching the upper 80s to low 90s over
  urban and coastal areas.

* Low to moderate concetrations of Saharan dust particles will
  promote hazy skies and deteriorated air quality across the
  region.

* Afternoon showers and thunderstorms are expected each day across
  portions of central and western Puerto Rico.

* The U.S. Virgin Islands can expect a mix of sunshine and passing
  showers, mainly during the morning hours.

&&

.SHORT TERM...Today through Sunday...

Current satellite derived precipitable water (PWAT) values indicate
below normal moisture over the islands (1.34 to 1.51 in) with the
lowest values over the SW quadrant of Puerto Rico and the highest
values over eastern Puerto Rico, including Vieques and Culebra, and
the U.S. Virgin Islands. Since midnight, radar estimated
accumulations over land have been minimal to locally low, mainly
over St. Thomas, St. John, Vieques and north-central to eastern
Puerto Rico. This was due to overnight passing showers under ENE
steering flow. Patches of drier air and low level moisture will
continue to reach the islands during the period, under ENE flow
today and ESE flow on Saturday and Sunday, with most available
moisture remaining below 800 mb. PWAT values over 2 inches will
likely be limited to afternoon convection during the period. Notable
advective patches of moistures (with PWAT values around 1.85 in) are
forecast to arrive by tonight into early tomorrow and by late Sunday
night and into the long term period. An upper low will continue over
the region to end the week, moving away on Sunday, leaving ridging
aloft. In general the diurnal pattern of morning and night passing
showers across windward areas of Puerto Rico and the US Virgin
Islands, and isolated to scattered afternoon convection, mainly over
western Puerto Rico, will continue. Sea breeze convergence, local
effects, and diurnal heating will promote this afternoon shower and
t-storm activity over western PR each afternoon with the risk of
excessive rainfall being limited to elevated. Steering flow during
the period can promote convective activity over more W-SW PR today
and W-NW PR on Saturday and Sunday, with lines of showers also
forming downwind of El Yunque and the USVI. A plume of Saharan Dust
will continue to affect the islands during the next couple of days
bringing up to locally moderate concentrations during the weekend.
This can deteriorate air quality and promote hazy skies.

Maximum temperatures will still reach the upper 80s to low 90s over
urban and coastal areas of the islands, with heat indices surpassing
105F. A Heat Advisory is in effect today from 10 AM to 5 PM AST for
urban and coastal areas of Puerto Rico. A limited heat threat is
also present today for the U.S. Virgin Islands, Vieques and Culebra.
Minimum temperatures will be in the upper 70s and low 80s at coastal
and urban areas, and the upper 50s to low 70s at higher elevations.
Similar heat conditions are forecast for the rest of the short term
period, with a limited to elevated heat risk.

.LONG TERM...Monday through Friday...

The uncertainty for the long term forecast continues regards the
development of a tropical wave, Invest 96L, located over the central
tropical Atlantic with a formation chance of 60% in the next 7 days.
The latest model guidances continues to suggest the passage of the
wave to the northeast of the region and away over the open Atlantic
waters on Monday. However, trailing moisture associated with this
system will reach the islands by early Tuesday. Therefore,
enhancing the potential to observe showers and isolated
thunderstorms across the U.S. Virgin Islands and Puerto Rico.

By Wednesday, a mid-to-upper level ridge will place over the
northeastern Caribbean promoting drier and stable conditions aloft.
A dense Saharan Air Layer (SAL) is expected to arrive into the
region from mid-week onwards, with moderate to high concentrations
of Saharan dust particles. Under the aforementioned conditions,
limited shower activity is anticipated during this period.

The 925 mb temperatures will remain at normal to above-normal
climatological values for next week. Highs will remain in the upper
80s to low 90s along the coastal and urban areas, and from the low
to mid 80s in the higher elevations. Heat indices will continue over
the 100 degrees Fahrenheit each day. Plan accordingly if planning to
do outdoor activities under sun exposure.

By the end of the workweek, model guidances are suggesting a
strong tropical wave to move into the central Atlantic. However,
there is a lot of uncertainty regarding the future of this system
as it is too early to specify possible impacts, if any, to our
region. Residents and visitors are strongly encouraged to stay
informed and monitor future forecasts as we move into next week.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions through the forecast period. Passing SHRA will
continue to move through the region, moving over the VCTY of TIST,
TISX, TJSJ and TJBQ during the morning hours. ENE flow up to 15 to
20 kts with higher gusts will steer these SHRA and promote SHRA/ISOL
TSRA mainly near the vicinity of TJBQ and possibly TJPS at around
08/17z to 08/22z. Winds decreasing after 08/22Z while gradually
veering to become more ESE.

&&

.MARINE...

Mariners can expect a moderate to fresh easterly wind flow
generating moderate chops across the local waters. Afternoon
convective activity will produce showers and thunderstorms across
the Mona Passage each day. An induced surface trough will move near
the region by Saturday or Sunday, increasing the available moisture
and the potential for showers and thunderstorms across the local
waters.

&&

.BEACH FORECAST...

Today, there is a low risk of rip currents at all beaches in
Puerto Rico and the U.S. Virgin Islands. However, it`s important
to note that even with a low risk, life-threatening rip currents
can still occur near groins, jetties, reefs, and piers. This low
risk is expected to continue until early Sunday, when a moderate
risk of rip currents is anticipated to return along the north-
central coast of Puerto Rico.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001>005-007-008-010-011.

VI...None.
AM...None.
&&

$$

MIDNIGHT CREW...MRR/GRS

NWS SJU Office Area Forecast Discussion