Federal experts have now issued a tsunami advisory for possible dangerous currents in coastal areas of California and Oregon following a magnitude-8 earthquake in the Pacific Ocean near Samoa.

The National Oceanic and Atmospheric Administration's West Coast and Alaska Tsunami Warning Center says an advisory means that a tsunami capable of producing strong currents or waves dangerous to persons in or very near the water is imminent or expected.

The center says widespread inundation is not expected.

The initial wave arrivals will begin about 9 p.m. Tuesday and build toward the most hazardous period early Wednesday morning.

Warning center official Guy Urban says a tsunami of 12 inches to 26 inches has been measured since the earthquake. Urban says it would be dangerous to people swimming or on beaches near the water.