Repto Horizonte, Puerto Rico Weather Forecast Discussion

073
FXCA62 TJSJ 101840
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
240 PM AST Wed Sep 10 2025
.KEY MESSAGES...
* Showers and thunderstorms will develop each afternoon,
  particularly across the northwest quadrant of Puerto Rico,
  increasing the risk of flooding rainfall and frequent
  lightning.
* The US Virgin Islands can expect a mixture of sunshine and
  clouds with little to no rain through the rest of the week.
* Moderate concentrations of Saharan dust particles will be
  present in the area from this afternoon through Thursday,
  gradually decreasing on Friday.
* Warm to hot heat indices will persist across urban and coastal
  locations in the US Virgin Islands and Puerto Rico.
* There is a moderate risk of rip currents for the northern and
  east-facing beaches of Puerto Rico and St. Croix tonight and
  Thursday, decreasing to a low risk for the weekend.
&&
.SHORT TERM...Rest of today through Friday...
Radar and satellite imagery showed that mainly fair weather
conditions prevailed this morning across the majority of the
forecast area. From mid-morning onward, cloudiness has been
developing, with some light showers moving into the vicinity of
the USVI and eastern municipalities of Puerto Rico, with no
impacts or significant accumulations. The main weather concern has
been the warm temperatures and high heat indices. Daytime
temperatures have been in the upper 80s to low 90s across urban
and coastal areas and the USVI, and in the upper 70s to low 80s
across the mountains. Heat indices have been ranging above 105
degrees Fahrenheit. A Heat Advisory remains in effect for the
urban and coastal areas of the US Virgin Islands and Puerto Rico,
as well as the valleys of the eastern interior of Puerto Rico.
Remember to stay hydrated and recognize the signs of heat stroke.
A surface high pressure system across the central Atlantic will
promote east to southeast winds over the next few days. The latest
guidance shows precipitable water content between 1.80 and 2.00
inches, associated with the remnants of a weak tropical wave that
will continue to move away this afternoon. Even though rain has
been very limited so far today, high-resolution models still
indicate that some showers will develop across the northwest
quadrant due to the combination of available moisture and diurnal
heating. Also, expect the arrival of moderate concentrations of
Saharan dust across the region from this afternoon onward,
allowing drier air to spread across the forecast area. This should
help limit the coverage of showers. The dust will remain in the
area from this afternoon through Thursday, gradually decreasing on
Friday. Individuals with respiratory problems are advised to take
the necessary precautions.
Regardless of the presence of Saharan dust, showers and some
strong thunderstorms are expected each afternoon tomorrow and
Friday, particularly over portions of western and northwestern
Puerto Rico. These conditions will be enhanced on Friday due to
the influence of a mid-to-upper-level trough lingering northeast
of the USVI. As a result, the flood risk will remain from limited
to elevated across portions of Puerto Rico through at least the
weekend. In contrast, the flooding risk for the U.S. Virgin
Islands will remain lower. Warm to hot heat indices will persist
across urban and coastal locations in the US Virgin Islands and
Puerto Rico over the forecast period.
.LONG TERM...Saturday through Wednesday...
.PREV DISCUSSION... /issued 449 AM AST Wed Sep 10 2025/
Model forecasts indicate that a mid-to-upper-level trough will
remain positioned to the northeast of the US Virgin Islands
(USVI), close to the Leeward Islands. This setup will generate
occasional easterly disturbances that will pass over our region
throughout the weekend. Subsequently, a mid-to-upper-level high-
pressure system is expected to build in from the northeast, likely
between Sunday and Monday. This development will enhance the
trade wind cap and introduce dry air with subsidence aloft.
Late Monday night into Tuesday, a tropical wave is predicted to
move into the Northeast Caribbean, which will increase moisture
levels and stimulate shower and thunderstorm activity.
Additionally, by the middle of next week, a mid-to-upper-level
trough will approach the area, interacting with the lingering
tropical moisture between Wednesday and Thursday.
Under the weather pattern explained above, residents and visitors
in the US Virgin Islands and Puerto Rico can expect excessive heat
that will affect most individuals sensitive to heat, especially
those without effective cooling and/or adequate hydration,
particularly in low-urban and coastal areas, each day through at
least Monday. However, the predominantly wind pattern will bring
occasional surges of moisture arriving on Saturday and early
Sunday. Then, by Sunday and Monday, a stable weather pattern and a
somewhat drier air mass will limit rain activity. Meanwhile,
strong afternoon convection will form each day across the interior
and western sections. The best chance to observe widespread
convective activity is between Tuesday and Thursday, associated
with Tuesday`s tropical wave, followed by the lingering mid to
upper-level trough interacting with abundant tropical moisture on
Wednesday and Thursday.
&&
.AVIATION...
(18Z TAFs)
Mainly VFR conditions across all TAF sites over the forecast
period. VCTS/-RA may result in brief periods of MVFR conds at TJBQ
in the next few hours. VCSH are possible during the overnight
period across USVI and TJPS TAF sites. Surface E winds around 8-12
kt with sea breeze variations, becoming lighter tonight.
SHRA/TSRA may result in brief periods of MVFR conds at TJSJ/TJBQ
tomorrow around 11/17Z onward.
&&
.MARINE...
A surface high pressure across the central Atlantic will promote light
to moderate east to southeast winds through the end of the week. A
weak tropical wave moving near the region can produce a few showers
and isolated thunderstorms across the regional waters this afternoon.
Moderate concentrations of Saharan dust particles will be present
in the area through Thursday slightly decreasing visibilities.
&&
.BEACH FORECAST...
Beachgoers, there is a moderate risk of rip currents for the
northern and east-facing beaches of Puerto Rico and St. Croix this
afternoon, tonight, and Thursday. Additionally, isolated
thunderstorms may develop each afternoon. If you hear thunder,
please move to a safer place indoors.
The risk is expected to decrease to low by Friday and into the
weekend. Although the risk of rip currents will be low, life-
threatening currents can still occur near groins, jetties, reefs,
and piers, so exercise caution. The risk is expected to increase
to moderate again early next week.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.
VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.
AM...None.
&&
$$
SHORT TERM/AVIATION...YZR
LONG TERM...CAM
PUBLIC...LIS

NWS SJU Office Area Forecast Discussion