One swell is declining, but a new swell is expected to push waves on north shores to 18 to 24 feet Wednesday, prompting the National Weather Service to extend a high surf advisory until 6 p.m. Wednesday.

The current swell is expected to diminish to 8 to 12 feet on north shores and 5 to 8 feet on west shores today. But the new northwest swell should start filling in tonight, forecasters say.

The advisory affects north shores of Oahu, Kauai County, Maui and Molokai and west shores of Kauai County and Oahu.

West shores should see 12 to 18 foot wave faces by Wednesday.

Forecasters say beachgoers can expect strong breaking waves, shore break and dangerous currents.