Tsunami advisory issued for Sonoma County, West Coast

A volcanic eruption in the Tonga Islands has triggered a tsunami advisory affecting the entire West Coast, with officials warning that waves are expected to hit the Sonoma Coast shortly after 8 a.m.

Although widespread inundation is not expected, residents are advised to stay off beaches, harbor docks and piers, according to an alert from the Sonoma County Sheriff’s Office, which also warned residents against traveling to the coast to view the event.

Triggered by the Hunga Tonga-Hunga Ha’apai volcanic eruption nearly 6,000 miles away, incoming waves are expected to be 1-2 feet high, officials say.

Those waves are capable of producing strong currents that may be hazardous to swimmers, boats and coastal structures, according to the Sonoma County Sheriff’s Office alert.

Further, officials warn that the incoming waves, emanating from the south Pacific, could last for hours.

“Tsunamis often arrive as a series of waves or surges which could be dangerous for many hours after the first wave arrival,” according to the Sheriff’s Office alert. “The first tsunami wave or surge may not be the highest in the series.”

The waves were expected to impact the Monterey Coast by 7:30 a.m., and hit San Francisco and the North Bay starting at 8:10 a.m.

By 7:20 a.m., Cal Fire had posted video to its Twitter account of surging waves at Miramar Beach in Half Moon Bay.

Shortly before 7 a.m., the National Weather Service Tsunami Alerts Twitter account detailed impacts to Hawaii, saying that the volcano-sparked waves had pushed boats up onto docks, but that no widespread inundation had occured.

About 8 a.m., Crescent City was on alert. The coastal community in Del Norte County is particularly prone to tsunamis, thanks in part to an underwater ridge offshore that helps intensify the surf before it reaches the coast.

The city has endured 32 tsunamis since 1933, including five damaging waves. The most recent, in 2011, destroyed more than a dozen boats.

By 8 a.m. Saturday, a publicly available live cam showed boats, bathed in golden morning sunlight, shuttling out of the harbor.

Inside bays and harbors, the effects are expected to be similar to king tides, which can flood low-lying areas but do not typically cause major damage.