A flash flood warning is in effect for Willow Brook Creek in Penngrove, near Petaluma, until 12:15 p.m., National Weather Service officials said.
Flash flood warnings mean that flooding is either occurring or is imminent. Authorities advise residents to avoid crossing swiftly flowing water of unknown depth, to move to higher ground if flooding is observed, and to report flooding to the nearest law enforcement agency.
The creek’s water level is expected to rise over the course of the morning and may lead to flooding further downstream in Petaluma, according to the National Weather Service.
The weather service has also issued urban and small stream flood advisories for Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, and Sonoma counties.
Streams and creeks may rise but property damage should be minimal, National Weather Service officials said.
“The heaviest rain is in Marin, Napa and Sonoma counties with up to a quarter-inch per hour,” National Weather Service forecaster Steve Anderson said.
Anderson said there have been reports of small hail and lightning in the Point Reyes National Seashore.
The weather service has also issued a high-surf advisory for areas along the coast including the Point Reyes National Seashore, the San Francisco Peninsula coast, northern and southern Monterey Bay and Big Sur coast.
The advisory will be in effect until 3 p.m. due to dangerous conditions related to tidal cycles, high winds onshore, and swells of up to 15 feet, according to the weather service.
“It’s slowly moving south,” Anderson said of the storm system.
“The greater Bay Area will start to see some of that heavy rain by midday.”
The greatest effects will be on the roadways, Anderson said.
The California Highway Patrol is alerting motorists of flooded roadways and road closures.
State Highway 29 is closed indefinitely due to snow between Bradford Road in Lake County and Tubbs Lane in Napa County, CHP officer Mark Thomas said.
The closure came about after the CHP responded to multiple crashes in that area.
“We’ve run out of patrol cars to get to them, so it’s closed indefinitely,” Thomas said.
Frei Road is closed at Graton Road in Sonoma County due to flooding, Thomas said.
The CHP is also warning motorists of flooding on southbound U.S. Highway 101 at Wilfred Avenue in Rohnert Park, U.S. Highway 101 at Highway 116 in Cotati, and state Highway 1 at Tomales Petaluma Road in Marin County.
Valley Ford Road at Bloomfield Road in Sonoma County is also flooded, with 3 to 4 inches of water on the roadway.
The CHP is urging drivers to use caution today.
“If people can leave a little extra space and use headlights it really helps,” Thomas said.
Wind advisories have been issued for the Richmond-San Rafael Bridge, the San Mateo-Hayward Bridge and the Bay Bridge, Thomas said. The advisories were issued Wednesday night and will stay in effect indefinitely.