With another winter storm bearing down on the Bay Area, the National Weather Service issued an updated set of warnings and advisories this morning.

A high surf advisory was upgraded to a high surf warning for Bay Area coastlines at 4 a.m., weather forecaster Matt Mehle said, meaning bigger waves than have been seen so far this week are likely.

“With a surf warning, the waves need to be in excess of 20 feet,” Mehle said. He said wave measurements at buoys 10 to 12 miles off the San Francisco coast were already at 21 to 25 feet as of 4 a.m.

A wind advisory went into effect at 5 a.m. Mehle predicted the incoming system will include sustained winds of up to 30 mph.

The wind advisory is set to become a high-wind watch tonight, with sustained winds of 40 mph expected and gusts of up to 58 mph a possibility.

The storm, which is expected to bring more rain and possibly thunderstorms and hail, has also prompted the weather service to issue a coastal flood watch for creeks, streams and other inland waterways, Mehle said.

The flood watch is set to take effect late tonight, and includes the Russian River watershed.

The U.S. Coast Guard recommends that people avoid beaches and low-lying coastal areas while storm conditions persist. Boaters are advised to avoid taking to the water over the next couple of days.

Any mariners who do venture out should leave a float plan with someone on land and check that all safety equipment is in working condition before departure.

Please make sure your comment adheres to our comment policy. If it doesn't, it may be deleted. Repeat violations may cause us to revoke your commenting privileges. No one wants that!