An unseasonably late northwest swell will be arriving on the North and West Shores of the Hawaiian Islands. This is resulting in a high surf warning for Niihau, Kauai, Oahu and Molokai. For Maui, the surf will be just one foot under the threshold for a high surf warning resulting in a high surf advisory. On north shores, wave heights should 20 to 24 feet later today and tonight. A swell of this size is pretty rare for Hawaii at this time of year. An extra large swell of this magnitude hit the islands in Easter of 1999. With light trade winds, it should be ideal conditions for big wave windsurfers. More casual ocean goers should exercise caution around the water as waves and currents will create dangerous conditions.