A surprisingly strong storm swept through San Diego County on Tuesday, causing scores of traffic accidents, leaving thousands without power, shuttering beaches and sinking at least one boat. While property damage and flooding were limited, the downpour flushed sewage-tainted pollution from Tijuana into South Bay beaches as far north as Coronado. The first major storm of season brought more than 2 inches of precipitation and winds up to 55 mph along parts of the coast and as much as 4 inches in the mountains with 70 mph gusts.