 Powerful surf rolled onto beaches on the west coast and Hawaii on Thursday is a big swell generated by the stormy Pacific Ocean pushed toward shorelines, causing localized flooding forecasters urged people to stay off rocks and jetties, and to not turn their backs to the ocean because of the danger of sneaker waves, occasional much bigger waves that can run far up the sand and wash someone off a beach.A high surf warning for parts of Northern California said waves would range from 28 to 33. Feet and up to 40 feet at some locations, the National Weather Service said, adding that there were reports of flooding in low-lying coastal areas.