A series of storms that began Saturday night and are anticipated to stretch into Friday will bring "moderate to heavy" rain and strong winds, National Weather Service forecaster Bob Benjamin said.
"One will lead right into the other, and each individual storm will be accompanied by periods of heavy rain and higher winds," he said.
"To have this progression, this number of systems, is not unheard of but it's not usual. If it progresses as anticipated, at the end, we will probably have to go back 10 years or more to find a system of equal rainfall and intensity," Benjamin said.
Residents should prepare for the rainfall and expect rivers and other bodies of water to rise, he said.
The San Francisco Public Utilities Commission and Department of Public Works issued a flood risk alert Sunday.
Residents and businesses in low-lying flood-prone areas are encouraged to prepare for potential flooding, and the city has put critical departments and storm weather responders on standby in anticipation of the storms, public utilities commission officials said.
The Department of Public Works is providing up to 10 free sandbags, filled or unfilled, to residents. The sandbags can be picked up at the DPW Operations Yard at 2323 Cesar Chavez Blvd. between 7 a.m. and 4 p.m. Monday through Sunday. Residents must show proof of residency.
Residents can call 311, the city's customer service center, for more information about sandbags or to report clogged storm drains, catch basins, flooding emergencies and sewer backups.
A wind advisory was also issued for the Bay Bridge Sunday, a California Highway Patrol officer said.
The advisory went into effect at about 4:55 p.m., CHP Officer Nicole Pacheco said.
She did not know when the wind advisory will be canceled. Drivers are urged to use caution when driving in high winds.