If you're heading out to the coast on this warm weekend, be aware of sneaker waves and rip currents that can drag unwary beach-goers out to sea, the National Weather Service warns.

A coastal hazard message has been issued for Sunday morning through Sunday evening from Marin and Sonoma counties to Monterey County. What is called "a long period northwest swell" heightens the risk for dangerous conditions on the beaches.

"It's not that the waves are going to be so high," said the National Weather Service's Bob Benjamin. "But the periods are so lengthy between waves that it frequently leads to sneaker waves and rip tides. If you wade in the surf up to your knees and the waves are just crashing up to your waist, all of a sudden a 10-foot wave can come in, crash over your head and drag you in. These are the kinds of situations when the sea might look relatively benign, but yet it's not."

Contact Paul Liberatore via email at liberatore@marinij.com