They are the result of a powerful El Nino, creating warmer than usual Pacific Ocean waters that generate thunderstorms packing heavy precipitation and high winds.
The weather service recently upgraded this year's El Nino from mild to strong.
"And as the ground becomes saturated, the winds begin to blow the trees, they begin to fall, power lines go down so people should prepare for power outages, to be prepared for hazardous driving conditions because there's going to be lowland flooding potentially," said David Reynolds from the National Weather Service.
One of the most powerful El Ninos that produced devastating storms plowed into the Bay Area during the winter of 1998.
