The National Weather Service says "very large and dangerous surf" is expected tomorrow and Friday on Oahu.

A large northwest swell will arrive in force sometime tomorrow, the weather service said.

A high surf advisory is in effect until 6 a.m. tomorrow but that is expected to be upgraded to a high surf warning for northern and western shorelines from 6 a.m. tomorrow until 6 p.m. Saturday.

The swell will first hit Niihau and Kauai and then move east along the island chain.

Surf should increase from the 12 to 16 foot level tonight to more than 20 feet by tomorrow.

Surf should rise rapidly reaching levels of 30 to 40 feet on northern shores by tomorrow night and the morning of Christmas Day, the weather service said.

Oahu's western shores may see 15 to 20 foot surf by tomorrow night and even higher surf is possible on western shores Christmas day.

A high surf warning means dangerous, battering waves will pound shorelines. This causes extremely dangerous swimming conditions with deadly rip currents.