The public works agencies in Marin County say they are monitoring the storm and feel as prepared as they can be.
LIVE VIDEO: Track the rain on Live Doppler 7 radar
But, towns like San Anselmo have been overwhelmed in the past by an unpredictable river.
Pictures hanging on the walls of the old town hall show the catastrophic flooding from 1982 and 2005.
"They had to shut down for a month or two. Some of them went out of business. It was a huge economic impact on the downtown," said Scott Schneider, Assistant Director for the San Anselmo Public Works Dept.
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Mary Edwards had just opened her real estate office about a month before the New Year's Eve flood in 2004.
Her building sits on the edge of the River. She lost everything.
"It went up about four feet into the building so everything got swept away."
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Most businesses along the avenue are ready for the coming storm.
Their flood gates, they hope, will protect them.
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