603
FXCA62 TJSJ 180928
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
528 AM AST Mon Aug 18 2025

.KEY MESSAGES...


* Major Hurricane Erin moving NW into the Western Atlantic will
  lead to southerly winds and external feeder bands that are
  resulting in showers, thunderstorms, and gusty winds. The Flash
  Flood Watch remains in effect through this evening.

* Shower interruptions are expected across the U.S. Virgin Islands
  throughout the day, with mostly ponding of water over roadways
  and poorly drained areas.

* Deteriorated marine and coastal conditions remain, with seas up
  to 10 feet mostly in the Atlantic waters, gradually improving
  throughout the day.

* Hazy skies and reduced visibility are expected by late Tuesday
  into Wednesday due a Saharan Dust Layer approaching the local
  islands, lingering through Friday.

* The National Hurricane Center currently monitors a tropical wave
  with 50% chance of formation in the next seven days. Interest in
  Puerto Rico and the U.S. Virgin Islands should continue
  monitoring this system.

&&

.SHORT TERM...Today through Wednesday...

High clouds from an outer band of Major Hurricane Erin kept the
skies cloudy through the night. Scattered showers popped up in the
Caribbean Sea, reaching the Virgin Islands, Vieques, Culebra and the
southern, eastern, and interior of Puerto Rico during the night
hours. Rainfall accumulations was heavy in some areas of the south
central and interior, with rainfall accumulations over an
inch.

For today, as Erin continues to move away from the region, the winds
will stay mostly from the south, bringing additional showers into
the region. These showers will affect mostly the southern portions
of Puerto Rico, and the municipalities of the Cordillera Central.
The risk of flooding will be elevated, with the potential for urban
and small stream flooding and rapid river rises in some areas. Gusty
winds and lightning are also expected too. For the Virgin Islands,
Vieques and Culebra, additional lines will move in at times, but the
rain should not be as conditions as it was during the weekend.
Some ponding of water on roadways can be observed. The temperature
forecast is tricky, mostly because of the cloud coverage. With
cloudy skies, it is unlikely that areas of widespread heat indices
above 105 degrees could develop, but if there is a break in the
cloud deck, then it could become hotter, probably requiring a Heat
Advisory for the region.

Conditions will dry out for Tuesday and Wednesday, with moisture
decreasing in the mid-levels. The trade winds will recover, coming
out of the southeast at 10 to 15 kts. With less clouds in the area,
temperatures will soar, with very hot conditions expected to
develop. Additionally, Saharan dust will move in late on Tuesday and
into Wednesday, resulting in hazy skies. Rainfall will be limited to
passing showers reaching the Virgin Islands and eastern Puerto Rico
at times, followed by afternoon convection in the northwest.

&&

.LONG TERM...Thursday through Monday...

Variable conditions are still expected over the long-term forecast.
Southeasterly winds are expected to gradually increase from Thursday
onwards as a surface high pressure over the Central Atlantic
migrates westward and lingers northeast of the CWA. PWAT values are
expected to drop to below and seasonal climatological normals (1.3 -
1.5 inches, with the 75th percentile reaching 1.75 inches). From the
latest GEOS-5/GMAO Dust Extinction product, pulses of a Saharan Dust
Layer (SAL) are likely to move over the region through Friday.
Although an upper-level low moving north of the islands is likely to
cool mid-level temperatures (around -7.5 degrees Celsius), deep
convection activity should be limited.

The National Hurricane Center continues monitoring a tropical wave
with a 50% chance of formation in the next seven days. From the
latest Tropical Weather Outlook (TWO), environmental conditions
are looking favorable for the gradual development of the system,
likely to become a tropical depression by the end of the week. As
mentioned in previous discussions, global models show this system
approaching the Caribbean Basin this weekend, although the time of
arrival and trajectory continue to differ. Based on the latest
deterministic guidance, the GFS suggests the system could arrive
by Friday night, while the ECMWF solution shows it approaching
the local area early Saturday. Nevertheless, ensemble models are
now tending to higher PWAT values on Saturday and Sunday (2.1 -
2.3 inches), increasing confidence. Although uncertainty remains
high, we could expect wet conditions by the upcoming weekend.
Resident and visitors should continue to monitor the development
of this system and stay tuned to the latest updates from the NHC.
By Monday, weather conditions should gradually improve across the
islands as a drier air mass may filter into the region.

Under a southeasterly wind flow, warmer temperatures, and available
moisture, heat indexes are likely to exceed 100 degrees Fahrenheit
and even meet Heat Advisory Criteria by the end of the workweek. Due
to the uncertainty regarding the weather conditions of the upcoming
weekend, the heat risk may undergo changes.

&&

.AVIATION...

(06Z TAFS)

SHRA/TSRA will be gradually decreasing, but still frequently
reaching TJPS today. These will cause periods of reduced VIS and low
ceilings, as well as stronger gusty winds. The wind flow is from the
south south at speeds around 10 to 12 kts in PR terminals, and
stronger for the USVI terminals, with speeds around 15 kts, gusting
22-28 kts. Wind speeds will begin to slow down after 22Z.

&&

.MARINE...

Erin`s outer bands are gradually diminishing over the region. However,
abundant moisture will persist, supporting periods of heavy showers,
strong thunderstorms and gusty wind conditions across the local
waters, though activity is expected to be less widespread than
earlier. Despite its continued northward movement, Erin will continue
to produce hazardous swell action that will impact the Atlantic and
Caribbean passages, but seas should continue to improve today. The
National Hurricane Center is also monitoring another tropical wave
with a medium chance of development in the next seven days, which
could be impacting the regional waters by the end of the workweek
into the weekend.

&&

.BEACH FORECAST...

High surf conditions are diminishing across the western, northern,
and eastern beaches of Puerto Rico and the U.S. Virgin Islands.
However, life- threatening rip currents are expected to continue
across eastern, northern, and western beaches of Puerto Rico
through at least this evening. Beachgoers are urged to avoid these
beaches. The risk of rip currents has lowered to moderate for the
beaches at the U.S. Virgin Islands, nevertheless, beachgoers
should exercise caution. The risk of rip currents should remain
moderate across the islands for the next few days, likely to
increase by the upcoming weekend.

Please refer to the latest Coastal Hazards Message (CFWSJU) and Surf
Zone Forecast (SRFSJU) for more information.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Flood Watch through this evening for PRZ001>013.

     High Rip Current Risk through this afternoon for PRZ001-002-005-
     008-010.

     High Surf Advisory until 6 AM AST early this morning for PRZ001-
     002-005-008-010-012-013.

     High Rip Current Risk until 6 AM AST early this morning for
     PRZ012-013.

VI...Flood Watch through this evening for VIZ001-002.

     High Surf Advisory until 6 AM AST early this morning for VIZ001-
     002.

     High Rip Current Risk until 6 AM AST early this morning for
     VIZ001-002.

AM...Small Craft Advisory until midnight AST tonight for AMZ711.

     Small Craft Advisory until 6 PM AST this evening for AMZ712-741-
     742-745.

&&

$$

SHORT TERM/AVIATION...ERG
LONG TERM...MNG