Swells as large as 18 feet, with wave faces much larger, repeatedly washed up to the vegetation line at beaches along the coast, said Lt. Pat Kelly, a city lifeguard with the North Shore station.

People were being advised to only go to beaches with lifeguards, because the surf this large can be unpredictable and dangerous, he said.

State Transportation Department spokeswoman Marilyn Kali said waves washed rocks and debris onto roads at Kea'au Beach Park in Makaha and at Ka'a'awa, but that the roads were passable and crews were dispatched to clear the debris.

The National Weather Service predicted this morning that the surf would gradually decrease through the day.