Powerful surf is rolling onto beaches on the West Coast and Hawaii as a big swell generated by the stormy Pacific Ocean pushes toward shorelines. Forecasters are urging people to stay off rocks and jetties Thursday, and to not turn their backs to the ocean because of the danger of “sneaker waves.” A high surf warning for parts of Northern California says waves will range from 28 to 33 feet and up to 40 feet at some locations. With high astronomical tides contributing to the problem, some low-lying coastal areas are experiencing localized flooding.