967
FXCA62 TJSJ 230752
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
352 AM AST Sat Aug 23 2025

.KEY MESSAGES...

* Abundant tropical moisture from a passing tropical wave and a
  approaching trough will result in showers and thunderstorms
  across the islands. This activity may result in localized
  flooding and frequent lightning.

* Marine conditions will continue to deteriorate today as swells
  from distant former Tropical Cyclone Erin reaches the region,
  promoting life- threatening rip currents, rough surf conditions,
  and Small Craft Advisory conditions through early next week.

* Weather conditions will improve from Sunday onward with the
  arrival of a drier airmass and a Saharan Air Layer. Limited
  showers, hazy skies and reduced visibilities are expected
  through mid-week.

* For the U.S. Virgin Islands, passing showers and isolated
  thunderstorms are possible today, particularly during the
  morning hours. Therefore, there is a limited risk of heat,
  excessive rainfall and lightning today.


&&

.SHORT TERM...Today through Monday...

Overnight, a tropical wave brought thunderstorms and cloudiness
mainly offshore, leaving minimal rainfall over land. Coastal low
temperatures stayed in the low 80s, likely a reflection of warmer-
than-normal sea surface temperatures (8586F) in the region, and
winds remained light and variable.

Hazardous weather is expected today across Puerto Rico and the US
Virgin Islands as abundant tropical moisture from a passing tropical
wave combines with favorable upper-level conditions from an
approaching trough. Precipitable water values will peak near 2.2
inches, while mid-level temperatures drop below -7C, creating a
highly conducive environment for showers and thunderstorms. Activity
will continue this morning over the USVI, Vieques, and southeastern
Puerto Rico, followed by a more intense round later today, mainly
across the interior and northern Puerto Rico, including the San Juan
metro area. Southeasterly winds will steer storms capable of
producing heavy rainfall, frequent lightning, and strong wind gusts.
The most significant risk is expected in northwestern Puerto Rico,
where urban and small-stream flooding is likely, and localized flash
flooding is possible.

Conditions will change significantly from tonight into early next
week as a mid-level ridge builds and both systems move away,
bringing much drier, more stable, and sunnier weather. Moderate to
fresh easterly trade winds will develop, transporting a Saharan Air
Layer across the region. As a result, precipitable water values will
fall well below normal, mid-level temperatures will warm, and a
trade wind cap will form. These factors will lead to limited shower
activity, hazier skies, reduced visibility, and poorer air quality.

For today, the primary weather concerns will be flooding, lightning,
and excessive heat. In fact, a Heat Advisory is in effect for 58
municipalities in the urban and coastal areas of Puerto Rico, with a
limited heat risk for Vieques, Culebra, and the USVI. Looking ahead
to Sunday, the risks of heat and localized lightning will persist,
while a risk of strong, non-thunderstorm winds will develop along
exposed coastal areas. By Monday, the weather will further
stabilize, with the primary concerns narrowing to just the
persistent heat and the coastal wind risk.


.LONG TERM...Tuesday through Saturday...

A dry weather pattern is expected for most of the long-term period
with the arrival of drier airmass and a Saharan Air Layer into the
region with moderate concetrations of Saharan dust. From Tuesday
into Wednesday a tropical wave is expected to pass south of the
area, enhancing the potential for shower development across the
local Caribbean waters and western Puerto Rico.

A strong surface high pressure in the central Atlantic will promote
easterly winds through mid-week. Then winds will shift from the
south-southeast in response to a long wave polar trough exiting
the US east coast. From Wednesday into the end of the week,
tropical moisture will be lifted from the warm Caribbean waters.
The latest precipitable water guidance has values of 1.60 to 1.70
inches, suggesting the potential for typical summer showers and
isolated thunderstorms across the region, in particular over the
northern and northwestern municipalities of Puerto Rico. During
this period, the U.S. Virgin Islands can expect mainly fair
weather condition and passing showers from time to time.

Hot temperatures are expected each day across Puerto Rico and the
U.S. Virgin Islands. Above-than-normal temperatures will persist
with highs in the upper 80s to low 90s along the coastal and urban
areas of the islands, to the low 80s in the higher elevations.
Residents and visitors are advised to monitor the weather updates
and plan accordingly if having outdoor activities under sun
exposure this weekend.

&&

.AVIATION...
(06Z TAFs)

VFR conditions will likely give way to MVFR, and briefly to IFR, as
SHRA/TSRA associated with a passing tropical wave moved inland this
morning and develop over land later this afternoon. For PR
terminals, these impacts are possible throughout the entire forecast
period, while the threat will continue through 23/23Z for USVI
terminals. Light and variable winds increasing to 10-15 knots with
occasional stronger gusts after 23/13Z, before diminishing again
after 23/22Z.

&&

.MARINE...

A tropical wave moving south of the area and a will promote showers
and thunderstorms today, mainly across the Caribbean waters and
local passages under a east southeast wind flow. A long period
northerly swell from distant Hurricane Erin will spread across the
islands from now onward, resulting in hazardous seas for the Atlantic
waters and Caribbean passages through early next week.

&&

.BEACH FORECAST...

Long period swells from distant former Tropical Cyclone Erin will
gradually fill across the Atlantic coastlines of the islands for
the next few days. This will promote life-threatening rip currents
and rough surf conditions across the northern exposed beaches of
the islands through Tuesday.

A High Rip Current Risk is in effect for the northern, eastern and
western beaches of PR, Culebra and the northern U.S. Virgin
Islands. A High Surf Advisory is possible for Sunday, or later
today if conditions warrant.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Monday afternoon for PRZ001-002-
     005-008-010-012.

VI...High Rip Current Risk through Monday afternoon for VIZ001.

AM...Small Craft Advisory from noon today to 6 PM AST Monday for
     AMZ711.

     Small Craft Advisory from 6 PM this evening to 6 PM AST Monday
     for AMZ712.

     Small Craft Advisory from noon Sunday to 6 PM AST Monday for
     AMZ716-723-741-742.

&&

$$

ICP/GRS