271
FXCA62 TJSJ 191800
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
200 PM AST Tue Aug 19 2025

.KEY MESSAGES...

* Hazy skies and reduced visibilities are expected through midweek
  due to the arrival of a Saharan Air Layer.

* Fair weather conditions are expected in general across the
  islands for most of the week. However, passing showers are
  expected from time to time across the USVI. Isolated afternoon
  thunderstorms are possible each day over western PR.

* A tropical wave in the eastern tropical Atlantic with a 60%
  chance of development into a tropical system is expected to
  bring an increase in thunderstorm activity from Friday through
  Saturday.

&&

.SHORT TERM...Rest of today through Thursday...

Sunny to partly cloudy skies prevailed across Puerto Rico and the
U.S. Virgin Islands today. However, high cirrus clouds and early
morning showers associated to an external band from Erin were
noted over portions of the islands. High temperatures were from
the upper 80s to low 90s across the lower elevations of the
islands. The wind was from the south to southeast between 12 to
16 mph with locally higher gusts at times.

A Saharan Air Layer with moderate to high concentrations of
Saharan dust will gradually filter over the region through
Thursday. This will promote hazy skies, reduced visibilities, and
poor air quality across Puerto Rico and the U.S. Virgin Islands.
Also, shower activity will be limited to localized afternoon
showers over portions of western PR each afternoon. Across the
USVI and windward areas of PR, passing showers are possible from
time to time. In addition, the combination of southeasterly winds
with enough shallow moisture content will cause hot temperatures
in general once again on Wednesday, and Heat Advisory conditions
are expected for the lower elevations and urban areas of PR and
the USVI.


.LONG TERM...Friday through Tuesday...

The end of the weekend and early next week will depend mostly on
the evolution of a tropical wave being monitored by the National
Hurricane Center. The wave is expected to reach the northeast
Caribbean Sea by late Friday and linger into Saturday. However,
the global models have been inconsistent in whether the wave will
develop into a tropical cyclone or if the center will move close
to the Virgin Islands and Puerto Rico, or just to the northeast of
the Leeward Islands. For now, the forecast show high probability
of precipitation for this time frame (60-80%), and an elevated
risk of flooding for the entire area of responsibility. The
reasoning is that even if the wave does not develop, enough
moisture will result in the development of showers and
thunderstorms. The users should continue to monitor the progress
of this system and stay tuned for further adjustments to the
forecast.

If the wave moves close enough or just over the islands, then it
is likely that an unsettled weather pattern will persist into
Sunday and Monday, but for now there is not too much confidence
in which scenario will prevail, so the chances of rain are around
40-50%. By Tuesday, drier air will filter in, with some Saharan
dust too. The weather is expected to be fair, although hot, very
hot. Temperatures are expected to be in the low and mid-90s, but
heat indices will surpass 105 degrees in most urban and coastal
area, as well as the valleys of the eastern interior of Puerto
Rico.


&&

.AVIATION...

(18Z TAFs)

Mainly VFR conditions are expected across all terminals during
the next 24 hours. HZ due to Saharan dust will continue to
increase during the next 24-36 hours across the area terminals,
and the VSBY may drop to around 6SM. Southeast winds will continue
between 10-15 kt, bcmg light and variable overnight.


&&

.MARINE...

Light to moderate southeasterly winds will continue through
midweek, becoming ENE from Thursday onward. A strong tropical
wave is expected to enter the eastern Caribbean on Friday,
increasing thunderstorm activity in general through Saturday.
This tropical wave has a medium chance 60% of developing into a
tropical system by the end of the week.


&&

.BEACH FORECAST...

A moderate risk of rip currents will prevail for all the beaches
of northern and western Puerto Rico, Culebra, and St. Thomas
through Wednesday. The risk is expected to increase to high from
Thursday onward as a northerly swell arrives and spreads across
the Atlantic waters and passages.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning until 5 PM AST this afternoon for
     PRZ001>005-007-008-010-011.

     Heat Advisory until 5 PM AST this afternoon for PRZ012-013.

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

AM...None.
&&

$$

SHORT TERM...DSR
LONG TERM....ERG
AVIATION...DSR
MARINE/BEACH...DSR