Forecaster Steve Anderson said a major storm will likely move into the Bay Area late today.
About half an inch of rain is expected by early Friday, Anderson said.
The rain comes after a warm period, which is typical in the Bay Area this time of year -- especially in San Francisco, which sees its warmest two months in September and October, Anderson said.
The brunt of the storm will hit Saturday, with about 2 inches of rain expected in the North Bay and Santa Cruz Mountains, and 1 inch in the rest of the Bay Area, he said.
"We'll see the outer fringes of it tonight and Friday, and the main cold front on Saturday," he said.
On Sunday a "cool, showery pattern" is expected, with light showers on and off throughout the day, Anderson said.
Light rain is expected Monday and Tuesday, he said.
A wind advisory will be in effect from 1 p.m. through midnight today, since winds are expected to increase as the storm approaches.
Gusts of up to 40 mph are expected while the advisory is in effect, with stronger winds along the coast, Anderson said.