The northwest swell that brought 30-foot waves to some shores Sunday is expected to continue through tonight.

The National Weather Service extended the high surf warning to 6 p.m. Tuesday for north shores of all islands except Lanai and Hawaii island, and west shores of Niihau, Kauai, Oahu and Molokai. A high surf advisory for Hawaii island’s west shore will also be in effect.

Waves up to 30 feet along north-facing shores and 15 to 20 feet along west-facing shores are expected, forecasters say.

Oahu lifeguards were busy Sunday, rescuing 17 people and taking 4,155 preventive actions at North Shore and Leeward Coast beaches, officials said.

Beachgoers are urged to stay out of the water and away from the shore break because of dangerous wave action and strong rip currents.

A small craft advisory also remains in effect until 6 p.m. Wednesday for Kauai northwest waters, with northeast winds expected to reach up to 23 mph tonight. The channels will see a northwest swell of 14 feet with scattered showers.

The wind speed is expected to increase to 29 mph Tuesday.