655
FXCA62 TJSJ 131808
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
208 PM AST Wed Aug 13 2025

.KEY MESSAGES...

 * The Saharan dust particles will linger across the islands
   until early tomorrow morning.

 * An increase in showers is forecast from late Thursday morning across
   eastern Puerto Rico and the U.S. Virgin Islands, associated
   with moisture from an easterly perturbation.

 * Tropical Storm Erin is forecast to move near the islands by
   late Saturday. As a result, residents can expect hazardous
   marine and coastal conditions from late Saturday through
   Monday. Please stay tuned for further weather updates on this
   tropical system.

 * For the U.S. Virgin Islands, residents and visitors should
   expect an increase in light to moderate showers tomorrow
   morning.

&&

.SHORT TERM... Tonight through Friday...

Variable weather conditions remained across most of the local
islands during the early morning hours, when showers moved across
northeastern sections of Puerto Rico, resulting in hazardous
driving conditions. Shower activity diminished at around 10 AM,
leaving the islands mostly under cloudy skies. At around 1 PM,
shower activity developed across interior sections moving
southward into the southwestern municipalities and Cabo Rojo.
Daytime temperatures were in the upper 80s and lower 90s across
most of the local coastal areas and in the urban sites. Heat
indices today were quite impressive, especially across northern
coastal areas, the San Juan Metro area, and the southwestern
coastal areas of Puerto Rico, with values approaching 110 to 112
degrees. Winds remained from the east-northeast at 10 to 15 mph
with gusty winds.

For the rest of the afternoon and into the night, conditions
should remain quite variable with the presence of afternoon
showers diminishing at around 7 PM AST. Passing showers from cold
advection are still forecast across the Atlantic waters tonight,
streaming along some northern coastal areas. For Thursday morning,
a slight area of dry air will move in; however, it will not last
long due to an easterly disturbance moving across the islands. At
the surface, winds will shift more from the east, resulting in a
showery pattern across eastern PR and focusing the afternoon
showers along the western interior section of Puerto Rico.
Conditions for Friday will depend significantly on the trajectory
and intensification of the now tropical storm Erin. As the system
approaches the Caribbean area, global models suggest an increase
in the presence of abundant tropical moisture. Given the potential
changes that may arise, discrepancies from this forecast could be
identified in the future. For now, however, the forecast calls
for a variable day with periods of cloudiness and moisture, as
outer bands associated with Erin move in and out of the region.
Therefore, residents can expect showers during the day,
particularly across northern Puerto Rico.


.LONG TERM...Saturday through Wednesday... from previous
discussion...

Based on the latest NHC`s trajectory and intensity forecast for
Erin, its center should move off to the northeast of the Northeast
Caribbean around early Sunday morning. However, Erin`s external
rain bands could arrive as early as Saturday morning and most
likely around Saturday evening. Our readers should be made aware
that the NHC track forecast has an average error of 150-215
statute miles at 4 and 5 days, so we expect future adjustments to
the forecast. Thus, we encourage everyone in Puerto Rico and the
U.S. Virgin Islands to keep an eye on Erin over the next few days,
as the intensity and track forecast will undergo changes, and our
weather conditions depend on its progress. That said, this
forecast will bring squally weather, especially for the US Virgin
Islands and the windward locations of PR, on Saturday.

As Erin follows the NHC track forecast, winds will shift from the
south to southwest around Sunday, pooling plenty of tropical
moisture over the islands, increasing the potential to observe
urban flooding, landslides, and river flooding, as well as
mudslides along steep terrains. The areas where the most active
weather will remain possible will be the US Virgin Islands, the
southeastern slopes, the northeast, and the northeast interior
portion of PR. Keep in mind this is tied to the final behavior of
Erin, so the level of uncertainty is still high. The unsettled
weather pattern could extend even into Monday or Tuesday due to
the southerly wind flow that Erin could promote over the region.
Additionally, this wind flow combined with the plenty of tropical
moisture will likely promote a warm to hot spell, especially
between mid-morning and the afternoon.

Model guidance suggests the arrival of another tropical wave as
the winds reestablish from the east late Tuesday night into
Wednesday.

&&

.AVIATION...

Brief MVFR conditions are possible across TJPS until 13/20Z. VCSH
and TSRA will persist along the mountains, resulting in lower
ceilings and a reduction in VIS. At 13/23Z, winds will diminish,
becoming less than 10 kts, increasing again at 14/15Z from the
east. VCSH to -RA is forecast for all eastern TAF sites tomorrow
morning as cloudiness moves in.

&&

.MARINE...

No changes to the actual forecast. Moderate easterlies will
promote moderate chops across the regional waters through at least
Friday. NHC`s trajectory and intensity forecast moves Erin off to
the northeast of the Northeast Caribbean by early Sunday morning.
Based on this forecast, the external bands of Erin could impact
the region as early as early Saturday morning and most likely
around Saturday evening. Under this weather pattern, marine
conditions will deteriorate by the upcoming weekend. We encourage
mariners and visitors to monitor the evolution of Erin actively.

&&

.BEACH FORECAST...

No changes to the actual forecast.There is currently a moderate
risk of rip currents across the north and east-facing beaches in
Puerto Rico and the US Virgin Islands. Thunderstorms will develop
across the local waters due to an easterly perturbation and may
approach some coastal areas. Please exercise caution.

IMPORTANT: Erin`s swell action could deteriorate marine and
coastal conditions, creating life-threatening rip currents for
this upcoming weekend. Residents and visitors are urge to avoid
the coastal areas from Saturday afternoon trough Monday.

&&

.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...LIS
LONG TERM & MARINE....CAM