A tsunami watch for Hawai'i was canceled last night, but Civil Defense officials said they were concerned about a possibly dangerous combination of high surf, tides and currents on O'ahu's North Shore and Leeward Coast.

Waves of up to 22 feet were expected overnight and could combine with residual effects of an earthquake-generated surge to create dangerous conditions in coastal areas from Ko Olina to Kahuku, O'ahu Civil Defense spokesman John Cummings said.

The Pacific Tsunami Warning Center issued a tsunami watch after 5:30 p.m., when an 8.3-magnitude earthquake struck off Japan, prompting county and state Civil Defense officials to open emergency operating centers. The watch was canceled about four hours later when it became certain the earthquake had not generated any destructive waves, Cummings said.

But officials said they would remain on alert throughout the night to monitor high surf and strong currents.

The most dangerous time, when a high tide could combine with small tsunami-related surges, was expected shortly after midnight.

A high-surf warning was expected to remain in effect for the north and west shores of all islands through tomorrow.

Reach Mike Leidemann at mleidemann@honoluluadvertiser.com.