317
FXCA62 TJSJ 051735
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
135 PM AST Tue Aug 5 2025

.KEY MESSAGES...

*The risk for urban and small stream flooding is elevated through
  Wednesday across Puerto Rico,but decreasing by the end of the
  work week.

*Temperatures will continue to be warm to hot, with heat indices
  exceeding 100 degrees each day across Puerto Rico and the US
  Virgin Islands.

*A tropical wave over the eastern tropical Atlantic continues to
  have a 50 percent formation chance in the next 7 days. We
  encourage citizens and visitors to continue to monitor updates
  from the National Hurricane Center (TWOAT) and from NWS San
  Juan.

&&

.SHORT TERM...Tonight thru Thu...

Mostly clear to partly cloudy skies prevailed across the local
islands during the morning hours, becoming partly cloudy in the
afternoon. Shower activity has been observed across east Puerto
Rico and the US Virgin Islands as well as the southwest quadrant
of the island. Rainfall totals associated with these showers were
minimal so far. Nevertheless, these showers will continue to
prevail during the next few hours, dissipating by the early
evening hours. Mostly fair weather is expected across the local
islands tonight and overnight with a few passing showers possible
across windward areas.

The short term forecast is still on track. A mid-level ridge pattern
is expected to strengthen by the end of the forecast cycle as
trofiness moves west and away from the local islands. At lower
levels, an induced trough will continue to yield east northeast
winds through at least Wednesday, becoming more easterly Thursday
onwards. In terms of precipitable water, although a decrease in
precipitable water is expected Thursday and Friday as the
trofiness moves away, the trades will continue to bring patches of
moisture from time to time. As a result, Wednesday is expected to
be a transitional day with afternoon showers and thunderstorms
developing across much of central and western Puerto Rico. Once
the drier air mass encompasses the forecast area, expect a
seasonal weather pattern with afternoon showers focused across
west Puerto Rico on Thursday and Friday. Having said this, the
risk for urban and small stream flooding is elevated on Wednesday,
decreasing by the end of the work week. Temperatures will
continue to be warm to hot, with heat indices exceeding 100
degrees each day.

.LONG TERM...Fri thru Tue/Issued 423 AM AST Tue Aug 5 2025

The latest model guidance continues to suggest Friday as the warmest
day of the long-term period with 925 mb temperatures in the 75th
percentile or above climatological normals with heat index values
exceeding 100F. As a result, a limited to elevated heat risk is
expected for coastal and urban areas, especially during peak
afternoon hours. A localized significant heat threat cannot be
ruled out. The 500mb temperatures should remain around -4 to -2
degrees Celsius, and the overall precipitation values below normal
for this time of the year, allowing the stable and fair weather
conditions to prevail.

Heading into the weekend, conditions will gradually become wet and
unstable as a Tropical Upper Tropospheric Trough (TUTT) begins to
establish to the northeast of the forecast area by Saturday. This
feature will enhance moisture and instability, leading to
occasional showers across the windward sectors of Puerto Rico and
the US Virgin Islands, with isolated afternoon showers and
thunderstorms over western Puerto Rico through Sunday.

Looking into early next week, model solutions continue to disagree
regarding the position, development, and timing of the tropical
wave now over the eastern tropical Atlantic. The Global Forecast
System (GFS) depicts a vigorous tropical wave approaching the
northeastern Caribbean, combining with the TUTT to enhance
instability and increase rainfall potential, while the European
Center for Medium Range Weather Forecasts (ECMWF) does not support
tropical development. The National Hurricane Center currently
gives the system a 50% chance of tropical development within the
next 7 days as it moves west-northwestward across the central
Atlantic.

Our forecast currently leans toward the GFS scenario, which
favors a transition to a wetter pattern early next week,
increasing the potential for deteriorating weather and rising
flood threats across Puerto Rico and the US Virgin Islands.
However, uncertainty remains high, and it is still too early to
specify exact impacts. Residents and visitors are strongly
encouraged to stay informed and monitor the latest forecast
updates as forecast confidence is expected to increase in the
coming days.

&&

.AVIATION...
(18z TAFs)

VFR conds will continue to prevail at all TAF sites with VCSH/VCTS
at JPS through about 5/22Z. VCSH likely at JSJ/IST and ISX early
the TAFs forecast cycle. ENE winds 15 to 20 knots to continue with
some sea breeze variations, becoming at 10 to 15 knots overnight.

&&

.MARINE.../Issued 423 AM AST Tue Aug 5 2025

No changes to previous discussion. A surface high pressure over
the central Atlantic will continue to promote gentle to moderate
winds. Winds will turn slightly to the east- northeast on Tuesday
as an induce surface perturbation move into the islands.

&&

.BEACH FORECAST.../Issued 423 AM AST Tue Aug 5 2025

No changes to previous discussion. The risk of rip current should
remain moderate along the northwestern beaches of PR through
tonight. There is a low risk elsewhere. Even if the risk for rip
currents is low, life- threatening rip currents often occur in the
vicinity of groins, jetties, reefs, and piers. Deteriorated air
quality is forecast to continue tonight as a plume of saharan dust
affects the islands.

&&

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

$$

SHORT TERM/AVIATION...OMS
LONG TERM/MARINE/BEACH FORECAST...MMC