578
FXUS66 KSGX 311550
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
850 AM PDT Sun Aug 31 2025

.SYNOPSIS...
Warm and dry today and tomorrow, with monsoonal moisture
increasing by Monday evening. Showers and thunderstorms possible
most of the day Tuesday and each afternoon in the mountains through
Thursday. Slightly cooler temperatures and a lesser chance for
storms in the mountains to end the week, with this pattern
prevailing into the weekend.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

.UPDATE...
Many locations this morning are already fairly warm despite the
return of a patchy marine layer, with above-normal temperatures
expected to persist nearly everywhere into Tuesday. Temperatures
peak on Monday before monsoonal moisture pushes up early Tuesday.
A slight uptick in rain shower/storm chances for Tuesday morning,
especially across the inland areas and coastal terrain, which may
help limit both afternoon high temperatures and thunderstorm
chances in the mountains/deserts for Tuesday. Otherwise, status
quo for the end of the week with a gradual cooling trend and
lesser chances of storms in the mountains each afternoon through
Friday.

&&

.PREVIOUS DISCUSSION FROM 247 AM...
Today through tomorrow...

Currently, there are low clouds beginning to form within the inner
waters of the SoCal bight, and some of these clouds are beginning to
penetrate into the coastal areas. This will continue to be the case
through the early morning hours, with some of the clouds making it
into the inland areas. There will likely also be some patchy fog,
especially along the coastal foothills. Patchy fog will also be
possible out over the open waters. This will all begin to dissipate
and break out with mostly clear skies expected for most locations by
shortly after sunrise. There are also some mid level clouds skirting
across the CWA this morning, which is an indication that some of the
monsoonal moisture in the mid levels is being advected in from the
southeast. Given this, there will be a very slight chance of an
isolated shower or possibly even a storm developing over the
mountains later this afternoon. Temperatures today under a roughly
595 dm high centered over northern Arizona will be above average
again, especially for the inland areas. By tomorrow, the ridge is
going to begin to expand further westward and allow for highs to be
even warmer tomorrow, with highs likely topping out above the 100
degree mark for most locations within the Inland Empire (IE). For
this reason, a Heat Advisory is in place tomorrow for all of the
inland areas, including Orange and San Diego counties. There will
also be an ample amount of mid-level monsoonal moisture moving over
tomorrow, which may allow for showers and isolated thunderstorms to
even make their way over some of the inland areas. This could also
help to hold down temperatures a bit for the desert areas, so likely
there will not be any need for an Excessive Heat Watch or Warning
for these areas.

Tomorrow night through the upcoming weekend...

There will be mid-level monsoonal moisture being advected in over
the region from the southeast by later in the evening tomorrow and
into Tuesday, which will allow for a chance of showers and/or
thunderstorms, even for some of the inland areas and even a slight
chance all the way down to the coastal areas during the earlier
hours of the morning on Tuesday. This could also hinder some of the
inland areas from getting quite as hot, although with the higher
humidity values, heat indices will still be high enough to warrant
the Heat Advisory continuing into Tuesday as well for the inland
areas. There could also be a few storms developing over some of the
inland areas by later in the day as well, although mid-level
steering flow will be rather weak, and it is more likely that a
majority of the showers and storms that form later in the day will
remain mostly confined to the mountains and deserts. Again, the
relatively elevated levels of near-surface moisture in the deserts
will keep them relatively cooler. Monsoonal moisture will remain in
place through Wednesday. By Thursday, there will more of a
southwesterly flow in the mid-levels, which translates to
relatively drier air being advected in and likely cutting off the
moisture source, with decreasing chances of thunderstorm activity
throughout the rest of the week and into the following weekend.
Temperatures will begin to gradually cool going into the following
weekend as well, as the ridge begins to slowly breakdown and
allow for more influence by the troughing upstream, although
remain slightly above average for most locations. The marine layer
will also become more persistent throughout the latter half of
the week as the onshore flow becomes more enhanced.

&&

.AVIATION...
311530Z...Low clouds near 400-700ft MSL will continue to dissipate
this morning off the coast. BKN low clouds with similar bases,
coverage and inland extent will build into the area after 08Z Mon.
This will be accompanied by areas of vis 1-3 sm with clearing near
15-17Z Mon.

Otherwise...VFR conditions for mountains and deserts with FEW-SCT
mid-level clouds developing over the mountains AOA 10,000 ft MSL
during the afternoons.

&&

.MARINE...
No hazardous marine conditions are expected through Thursday.

&&

.BEACHES...
A long-period (15-16 sec) southerly swell (180-200 degrees) will
bring elevated surf through Tuesday, gradually subsiding
thereafter. Surf of 3-6 feet with occasional sets to 7 feet for
south-facing beaches. Longshore currents along west-facing beaches
with a high rip current risk for all beaches. Beach Hazard
Statement in effect through late Monday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Monday evening for Orange County
     Coastal Areas-San Diego County Coastal Areas.

     Heat Advisory from 10 AM Monday to 6 PM PDT Tuesday for Orange
     County Inland Areas-San Bernardino and Riverside County
     Valleys-The Inland Empire-San Diego County Valleys-Santa
     Ana Mountains and Foothills.

PZ...None.

&&

$$

PUBLIC...Zuber
AVIATION/MARINE/BEACHES...APR