493
FXCA62 TJSJ 190720
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
320 AM AST Tue Aug 19 2025

.KEY MESSAGES...

* Extreme hot conditions are expected today across Puerto Rico,
  especially along urban and coastal areas, as well as the valleys
  of the eastern interior. This level of heat will affect anyone
  without effective cooling or adequate hydration.

* An elevated heat threat is also expected for the Virgin Islands,
  Vieques and Culebra, impacting those sensible to heat and
  without effective cooling or that are not adequately hydrated.

* Saharan dust will arrive in the Virgin Islands later today, and
  then reaching Puerto Rico. Hazy skies are expected until at
  least early Thursday.

* The National Hurricane Center continues to monitor a tropical
  wave in the middle of the Atlantic Ocean. This wave is expected
  to approach both territories by Friday or Saturday, at least
  increasing the potential for showers and thunderstorms. Stay
  tuned for further updates on this system.

* Marine conditions have improved, but a long-period northerly
  swell is expected this weekend, impacting seas and beaches in
  Puerto Rico and in the Virgin Islands.

&&

.SHORT TERM...Today through Thursday....

Showers and isolated thunderstorms were seen overnight due to
lingering moisture and external bands associated with Hurricane
Erin, now located north of the Turk and Caicos Islands. This
activity mainly affected portions of southern Puerto Rico. Doppler
radar estimated rainfall accumulations were less than 1.0 inch across
Ponce and Juana Diaz. Across the U.S. Virgin Islands, mainly fair
weather conditions prevailed with few passing showers across the
area. It was very warm overnight as well, with lows in the upper
70s to the low 80s along the coastal and urban areas of the
islands.

Today, moderate to high concentrations of Saharan Dust will reach
the local islands, promoting hazy skies, reduced visibilities and
deteriorated air quality through at least early Thursday. With
the anticipated pattern, limited showers are expected today.
However, localized activity is anticipated to occur over central
and western Puerto Rico due to daytime heating and local
orographic effects.

A warm pattern will take over the region for the next few days due
to the combination of southeasterly winds, high temperatures and the
available moisture. Highs are expected to reach the upper 80s to the
low 90s with heat indices above the upper 100 degrees Fahrenheit
along the coastal and urban portions of Puerto Rico and the U.S.
Virgin Islands. Today, a Extreme Heat Warning is in effect from 9 AM
to 5 PM AST for the eastern interior and all coastal areas of Puerto
Rico. In addition, a Heat Advisory is in effect for Culebra, Vieques
and the U.S. Virgin Islands from 9 AM to 5 PM AST. Residents and
visitors plan accordingly if planning to do outdoor activities under
sun exposure.

.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...
(06Z TAFs)

Mainly VFR conds expected across all terminals during the next 24
hrs. SHRA/TSRA will continue today due to lingering moisture and
external bands from Hurricane Erin, particularly over TJPS/TJBQ/TJSJ
aft 19/14Z. Southeasterly winds will prevail btw 10-15 kt, with
higher gusts and sea breeze variations.

&&

.MARINE...
Erin`s outer bands are gradually diminishing over the region, but
some showers and thunderstorms continue across the Caribbean waters
and Mona Passage. Saharan dust will arrive later today, lasting into
early Thursday. This will result in hazy skies and mostly dry
conditions. As Hurricane Erin continues to move into the far north
Atlantic Ocean, a long-period northerly swell will arrive this
weekend, extending into early next week. Additionally, the National
Hurricane Center is monitoring a tropical wave over the central
Atlantic. This wave is expected to be near the region by late Friday
and Saturday, at least increasing the potential for showers and
thunderstorms.

&&

.BEACH FORECAST...
Conditions are gradually improving along the local beaches.
However, there is still a moderate rip current risk for all the
beaches of northern and western Puerto Rico, Culebra, and St.
Thomas. Also, be aware of thunderstorms in the area and seek
shelter immediately if you hear thunder.

Beach conditions are expected to deteriorate again late in the
week and into the weekend as a northerly swell arrives, and as a
tropical disturbance approaches the region.



&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning from 9 AM this morning to 5 PM AST this
     afternoon for PRZ001>005-007-008-010-011.

     Heat Advisory from 9 AM this morning to 5 PM AST this afternoon
     for PRZ012-013.

VI...Heat Advisory from 9 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...GRS
LONG TERM....ERG