Escuela Theodore Roosevelt, Puerto Rico Weather Forecast Discussion

828
FXCA62 TJSJ 091853
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
253 PM AST Tue Sep 9 2025
.KEY MESSAGES...
* An unstable weather pattern will prevail tonight into
   Wednesday along the islands due to a surface trough moving
   across the CWA.
* A warm trend is forecast due to the east-southeasterly winds
   along the islands, triggering an elevated heat threat along
   the islands.
* The rip current risk will increase to moderate for the
   northern coastal areas on Wednesday.
* For the U.S. Virgin Islands, for tonight into tomorrow the
   islands can expect mostly a variable pattern with light to
   moderate showers diminish by Thursday.
&&
.SHORT TERM...Tonight through Thursday...
The morning remained relatively quiet and stable, with no shower
activity across the islands and only some cloudiness mainly
affecting the U.S. Virgin Islands. Conditions rapidly changed as a
plume of moisture from a surface trough moved westward into the
region, increasing shower activity over St. Croix and the El
Yunque area in the northeast corner of Puerto Rico. Showers and
thunderstorms eventually developed across the San Juan
metropolitan area. This activity became intense around Trujillo
Alto and Gurabo, later spreading into Carolina and San Juan.
Additional showers extended across the Cordillera Central,
affecting interior municipalities like Orocovis and Barranquitas
with nearly two inches of rain. Warmer conditions were also
observed during the day, with heat indices reaching 108 to 110
degrees along the north-central coast of Puerto Rico and the
southern coastal plains.
For the rest of the afternoon and into the evening, instability
and cloudiness will persist due to the influence of the
approaching surface trough. As a result, residents can expect an
unsettled night with periods of light to moderate showers,
especially across the eastern windward sections of the islands.
Tomorrow, global model guidance suggests the arrival of a tropical
wave, maintaining a surge of tropical moisture across the region.
Given the evolving pattern, another round of variable weather is
forecast, with morning cloudiness followed by afternoon convection
developing over the Cordillera Central and moving into
northwestern Puerto Rico. On Thursday, winds will continue from
the east-southeast. Under this pattern, the islands will
experience patches of shallow moisture along with Saharan dust
particles, resulting in brief hazy skies and periods of light to
moderate showers, particularly over the western interior.
Additionally, the presence of abundant tropical moisture combined
with variable morning conditions will sustain warmer-than-normal
temperatures. Consequently, an elevated heat threat remains in
place for the short-term forecast.
.LONG TERM...Friday through Tuesday... from previous discussion
issued at 425 AM AST Tue Sep 9 2025...
Model guidance continues to suggest the mid-to-upper-level trough
lingering off to the northeast of the USVI, near the Leeward
Islands, inducing occasional easterly perturbations that will
arrive across our region through at least Saturday. Then, a mid-
to-upper-level high-pressure system will build from the northeast
into our islands between Sunday and early next week, strengthening
the trade wind cap and promoting dry air with subsidence aloft.
Monday and Tuesday, tropical moisture from easterly perturbations
will be moving across the Northeast Caribbean, enhancing shower
and thunderstorm activity.
Residents and visitors of the USVI and PR should prepare for more
frequent surges of moisture arriving on Friday and Saturday. This
will be followed by a more stable weather pattern from Sunday to
Monday morning. After that, a tropical wave is expected to
increase shower and thunderstorm activity, particularly during the
afternoon and evening hours on Monday and Tuesday.
Some factors that could promote strong afternoon convection,
particularly in the western regions of Puerto Rico and downwind
from the US Virgin Islands, are the excessive heating that we are
forecasting, as well as the lingering Saharan Air Layer with low
to locally higher concentrations in the area (especially on
Friday). Additionally, the nighttime cool air advection over the
above-normal sea surface temperatures will lead to scattered to
numerous showers, especially during the latter part of the week.
Once again, warmer-than-normal maximum and minimum temperatures
could extend the potential to observe excessive heating each day,
with heat indices potentially exceeding 100 degrees Fahrenheit,
attributed to the existing east-southeast wind patterns.
Consequently, the risk associated with heat will remain elevated
throughout the forecast period.
&&
.AVIATION...
SHRA to TSRA will enhance briefing MVFR conditions along the
Puerto Rico TAF sites for the upcoming hours until 09/23Z. For the
rest of the area, lower ceilings are possible, especially across
the mountains, due to the most vigorous shower activity. Winds
will continue from the east-southeast, diminishing at around
09/23Z, increasing again at 10/15Z. VCSH is forecast for TIST &
TISX from 10/00-10/12Z.
&&
.MARINE...
No significant changes to the actual forecast. The combination of
the surface high pressure across the central Atlantic and a front
over the western Atlantic will promote light to moderate east to
southeast winds through the end of the week. Localized hazardous
marine conditions are forecast for tonight into tomorrow morning
as the surface trough continues to result in moderate to strong
showers across, resulting in localized higher seas. Mariners are
urged to exercise caution near the thunderstorms for the rest of
the afternoon into the evening hours.
&&
.BEACH FORECAST...
There is a low risk of rip currents across all the local exposed
beaches along the Puerto Rico islands, and a moderate risk of rip
currents for St. Croix. The risk of rip current will increase to
moderate along the northern coastal areas of Puerto Rico on
Wednesday, prevailing at least until Thursday night. Residents and
visitors are urged to stay tuned to the non-designated swim areas.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>005-007-
     008-010>013.
VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.
AM...None.
&&
$$
SHORT TERM & AVIATION... MORNING CREW
LONG TERM.... MIDNIGHT CREW
AVIATION...LIS

NWS SJU Office Area Forecast Discussion