As the Bay Area endures its wettest January in 15 years, yet another winter storm with predicted significant rainfalls and high winds with the potential to take down trees and power lines is expected to hit the region Saturday night into Sunday, according to the National Weather Service. Steady rain could begin as early 8 p.m., with the heaviest downfalls expected between 2 and 4 a.m. as the storm comes in from the north, said Brian Garcia, a forecaster in the service’s Monterey office, on Saturday.