FXUS66 KMTR 040056
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
556 PM PDT Thu Sep 3 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1147 AM PDT Thu Sep 3 2026
- Well below normal temperatures with beneficial rain Thursday
- Hazardous beach conditions at Pacific Coast beaches Friday
through Monday
- Below normal temperatures through the weekend, gradual warming
and drying trend Monday through Wednesday
&&
.SHORT TERM...
Issued at 1147 AM PDT Thu Sep 3 2026
(Thursday through Thursday night)
Cloud cover will increase through the day as a cold front approaches
from the northwest. FROPA will occur this afternoon into this
evening from northwest to southeast. The standard wind shift from
southeasterly to northwesterly will occur pre and post-frontal,
respectively, with gusts up to 25 mph to be expected. Gusts of 30-40
mph are expected through terrain favored gaps and passes such as The
Delta, Altamont Pass, and Pacheco Pass, as well as down the Salinas
Valley. For the North Bay, rainfall totals up to 0.25" with locally
higher amounts up to 0.75" in the higher terrain are expected. South
of the Golden Gate Bridge, less than 0.10" is expected with
accumulation favoring the coast and higher terrain with the help of
orographic lift. Overperformance is still a possibility with the
struggles of guidance/models in the early season. While rainfall is
expected to be beneficial, wet roadways will create slick driving
conditions and increase stopping distance. With ample low-level
moisture and post-frontal clearing, the marine layer will try to
reform tonight. As a result, patchy fog/stratus will be possible for
the Friday morning commute.
&&
.LONG TERM...
Issued at 1147 AM PDT Thu Sep 3 2026
(Friday through Wednesday)
The most impactful weather phenomenon Friday through Monday will be
hazardous conditions at Pacific Coast beaches. Two sets of long
period southerly swell from distant Hurricane Karina and Hurricane
Marie will result in an increased risk for sneaker waves and strong
rip currents with breaking waves up to 10 feet. With pleasant
sensible weather expected, these are the type of days that are most
deadly; with it being the Labor Day holiday weekend, that will
likely only make matters worse. If you want an outdoor activity this
weekend, hit the trails instead of the beach. There's good agreement
through the weekend that there will be an upper-level low over the
Pacific Northwest which will keep our region under the influence of
troughing. As such, expect below normal temperatures and onshore
flow to continue with the return of the marine layer. The forecast
is now dry this weekend with the farther west track of Marie and dry
air filtering in from the northwest. Uncertainty arrives Monday in
terms of low versus trough, but global ensemble clusters are in
agreement that the pattern becomes progressive again as the low
begins to fill and move east. This will allow for ridging to build
in from the Desert Southwest, kicking off the gradual warming and
drying trend. It is now looking likely that at least some of Marie's
remnant moisture will eventually be brought into our area as soon as
Tuesday. Whether this transpires as clouds or rainfall will be
dependent on the reinforcing low/trough and the strength of the
flanking ridges. Right now, the official forecast has light rainfall
Tuesday through Thursday favoring the Central Coast.
&&
.AVIATION...
(00Z TAFS)
Issued at 556 PM PDT Thu Sep 3 2026
The front is slowly meandering across northern CA this evening, with
light to moderate rain being observed across the North Bay. Chances
for rain will gradually decrease through the evening hours for
terminals up there, while chances increase slightly for the rest of
the Bay Area terminals this evening. The front begins to fizzle out
as it advances towards the Central Coast, so lower cigs and perhaps
some virga might be all we get. Behind the front, northwest winds
usher in drier air. This makes any sort of fog/stratus forecast
tough for tonight. Opted to keep the trends from the previous met,
and have them arriving during the early overnight hours for most
sites. But that could be too optimistic and we'll need to re-
evaluate with the 6Z package.
Vicinity of SFO...SFO has bewildered us today with the low clouds
being quite pesky, and if you didn't guess it, that remains the
forecast challenge this evening. As the front passes, expect periods
of reduced cigs and perhaps some VCSH. VCSH should come to an end
between 03Z-05Z which may bring us a break in the periodic MVFR
cigs. After that, the HREF, HRRR, and NAM show moisture lingering
around KSFO all night and into tomorrow morning. The question will
be, do we get socked in with MVFR cigs or to we clear out a bit?
Opted to keep the pessimistic forecast for the time being with
conditions improving around or shortly after sunrise. Any low clouds
that linger should erode by mid to late morning. Breezy onshore
winds return for the afternoon and early evening hours, with
sustained speeds around 12-15kt with gusts up to 22-25kt possible.
Low to medium confidence in the low cloud forecast through sunrise.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...The front will slowly approach the region
tonight, bringing with it some mid and high level clouds. Ahead of
it, some stratus has formed on the northern side of the Monterey
Bay, while KSNS and KMRY remain cloud free. Models show the chance
for stratus building in between 01-04Z, with the front arriving
later. Looking at MVFR to IFR cigs tonight around the region, with
skies gradually clearing Friday morning.
&&
.MARINE...
(Tonight through next Wednesday)
Issued at 556 PM PDT Thu Sep 3 2026
Rain chances diminish over the northern waters through the night.
Gentle to moderate northwesterly breezes will persist across the
waters in wake of a weak frontal passage. However, diurnal fresh
to strong gusts return within the Monterey Bay and along the Big
Sur Coast Friday into the weekend. More widespread fresh to strong
gusts return by early next week across the coastal waters. Long
period southerly swell associated with tropical activity well to
our south will reach the coastal waters Friday and continue into
early next week.
&&
.BEACHES...
Issued at 1010 PM PDT Wed Sep 2 2026
A Beach Hazards Statement is in effect Friday-Monday as the swell
from both Hurricane Marie and Hurricane Karina reaches the coast.
As these hurricane whip up the ocean, the waves travel over 1,000
miles in all directions, gradually flattening out to low
amplitude, but long period swell. These waves aren't very
intimidating if you're on a boat in the open ocean, but the long
period allows them to push much farther up the beach. Long period
swell always increases the chance for sneaker waves, but that's
particularly true this weekend since there are 2 different sets of
southerly swell, and their energy will periodically combine. In
addition to sneaker waves, expect strong rip currents and
breaking waves up to 10 ft. As this is a holiday weekend and the
weather is otherwise pretty nice, the exposure to the risk is
high. Avoid the water if you're not an expert swimmer. If caught
in a rip current, swim parallel to shore until you stop feeling
the pull. Even on the beach, be prepared for sneaker waves this
weekend and never turn your back on the ocean.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from Friday morning through Monday
evening for CAZ006-505-509-529-530.
PZ...None.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...KR
MARINE...RGass
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Prepared by Boulder-Creek.com Weather at: Thu Sep 3 20:30:03 PDT 2026
From the National Weather Service
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