Marine Weather and Tide Forecast for Piedmont, CA

SHORT TERM
Issued at 1152 PM PDT Fri Oct 9 2026 (Tonight through Sunday)

Much cooler air quickly flowed inland Friday with about equally weighted northerly ACV-SFO and onshore SFO-SAC pressure gradients supporting northwest winds. Current 24 hour temperature trends remain sharply lower by up to double digits Fahrenheit across higher elevations and inland. Surface temperatures across the highly varied terrain in our forecast area show only a few places left at highest elevation that are still relatively mild from the mid 60s to lower 70s. Due to a pattern shift with upper level troughing forecast to dominate our weather through the weekend, the lower level temperature inversion is already steadily weakening and lifting. The marine layer depth continues to increase, currently between ~ 1700 and 2500 feet. Cooling applied to the marine layer with upsloping winds will produce light patchy drizzle from San Francisco southward to the Big Sur coastline, including the East Bay hills tonight and Saturday morning.

Cold air advection continues through Saturday greatly weakening the lower level temperature inversion that's capping the marine stratus. Expect plentiful vertical mixing with drier air and daytime surface heating to mix out the stratus by early afternoon.

Highs and lows Saturday and Sunday will be below to much below normal for the time of year. Highs in the 60s/70s, warmest inland.
Lows in the 40s/30s, coldest far inland valleys, except near 50 along the immediate coastline and bays.

LONG TERM
Issued at 1152 PM PDT Fri Oct 9 2026 (Sunday night through next Friday)

500 mb troughing will prevail with mainly drier air flowing southward across our forecast area early to mid next week. There may be a little light measurable shower activity in the southernmost forecast area later Sunday and Monday. However, recent NBM has trended drier to less than 0.10" liquid precipitation. 500 mb ridging will advance eastward over our forecast area mid to late next week, bringing a return to warmer daytime temperatures.

AVIATION
(12Z TAFS)
Issued at 412 AM PDT Sat Oct 10 2026

Primarily a mix of MVFR and VFR with a marine layer at ~2500ft from the 12z KOAK balloon. Drier air associated with a cold front currently pushing south through our area can be seen gradually eroding stratus both onshore and offshore early this Saturday morning. Current condition's should only improve from this point until clearing leads to VFR by mid-morning for the North Bay and Bay Area terminals, late morning for Monterey Bay sites.

Vicinity of SFO...VFR conditions are expected through the TAF period however MVFR cigs will persist in vicinity of terminals through mid-morning with gusty winds this afternoon and tonight in the wake of the cold front pushing through our area currently.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals.. MVFR ceilings will persist until late morning with VFR expected throughout the remainder of the TAF period. Breezy onshore flow will develop behind the advancing cold front later today and tonight.

MARINE
(Today through Thursday)
Issued at 412 AM PDT Sat Oct 10 2026

Dangerous conditions remain in place across our coastal waters this weekend. Strong northwest winds have begun to spread south as a cold front moves through. Expect frequent gale force gusts in exposed waters along with rough to very rough seas building in response to the strong winds. On top of the hazardous winds and rough wind waves, two sets of swell haver arrived, from both the south and west. The significant wave height will reach 16 feet in the northern outer waters.

BEACHES
Issued at 446 AM PDT Fri Oct 9 2026

Hazardous beach conditions will be present at Pacific Coast beaches Saturday through Monday. Long period southerly swell from distant Tropical Storm Rachel will build in height through the weekend, bringing an increased risk of sneaker waves and strong rip currents.
Long period westerly swell from a gale force low in the Central North Pacific will arrive Sunday, bringing breaking waves up to 16 feet. The large tidal swings will also result in coastal erosion as water and waves are brought farther up the beach than normal, especially during high tide. Remain off jetties, piers, rocks, and other waterside infrastructure as waves can sweep across the shoreline without warning, pulling people into the sea. Remain out of the water to avoid hazardous surf and strong rip currents and never turn your back on the ocean!

Sarment

MTR WATCHES/WARNINGS/ADVISORIES
CA...Coastal Flood Advisory until 3 PM PDT Tuesday for CAZ006-508-529- 530.

Beach Hazards Statement through Monday evening for CAZ006-505- 509-529-530.

Coastal Flood Advisory until 4 PM PDT Wednesday for CAZ506.

PZ...Small Craft Advisory until 3 PM PDT Sunday for Pigeon Pt to Pt Pinos 10-60 NM-SF Bay N of Bay Bridge.

Small Craft Advisory from 9 AM this morning to 9 AM PDT Sunday for Mry Bay.

Gale Warning until 9 PM PDT this evening for Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory until 9 AM PDT Sunday for Pt Reyes to Pigeon Pt 0-10 nm.

Small Craft Advisory from 9 AM this morning to 3 PM PDT Sunday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

Gale Warning until 9 AM PDT Sunday for Pt Arena to Pt Reyes 10- 60 NM.