BAY AREA — A brief but powerful storm was expected to hit the Bay Area Tuesday afternoon, which was forecast to grow heavier as night descends, accompanied by powerful gusts of wind.the storm, expected to arrive by around 4 p.m., could drop as much as 4 inches of rain in some North Bay locations and bring wind gusts as strong as 55 mph in some coastal areas and at higher elevations.because of the heavy rain, which could come down at a rate of an inch per hour, the weather service has issued a flash flood watch for Marin, Sonoma and Napa counties.the flash flood watch, which begins at 6 p.m., is expected to remain in effect until 4 a.m. Wednesday, when the most severe part of the storm will have moved out of the region, Cross said.Southerly winds of 20 to 30 mph were expected Tuesday night, with gusts of 45 to 55 mph possible on the coast and at elevations above 1,000 feet. the strongest winds are expected to subside by early Wednesday, according to the weather service.To help residents prevent flood damage, the city of Napa opened a self-service sandbag station Tuesday morning. People seeking sandbags should bring their own shovels and gloves and be prepared to fill and transport the bags.the sandbag station is located in the parking lot on the west side of Freeway Drive at First Street, city officials said.Drier weather was expected Wednesday, with mostly cloudy to partly cloudy skies, although scattered showers are also in the mix. Highs around 50 and northwest winds of 20 to 30 mph were anticipated.