Big waves rolling in

A large south swell caused by a storm in Tahiti could pound Newport Beach with waves up to 20 feet high later this week and into the weekend, forecasters predict.

Rolling in on Thursday afternoon, the swell should bring 5- to 8-foot surf through Saturday throughout Southern California, with south-facing beaches such as the Newport Peninsula drawing at least 10- to 12-foot waves.

The Wedge, at the mouth of the harbor, might get waves more than 20 feet high, said Sean Collins, the chief forecaster for Surfline.com, an industry leader in surf forecasting.

“This will be a very, very dangerous large swell. On Thursday, there will be very long lull periods of small or no waves, but then suddenly a series of very large waves will sweep over previously dry areas. This situation poses an extreme danger to unsuspecting people that may be walking over exposed rocky areas, exploring tide pools, or fishing from jetties or break walls,” Collins said in an e-mail.

The Wedge is unusual because of its extreme exposure to south swells and its unique wave shape.

As a wave comes in, it ricochets off the jetty that guards the harbor mouth, rejoining and reinforcing waves coming straight in and forming towering peaks.

It can also be especially dangerous because the waves break close to shore, with little water to cushion the falls of body surfers and board riders before they hit the sand.

Newport Beach lifeguards are already up to full staff for the summer, with all towers full. If the Wedge turns out to be as big as Surfline expects it to be, then another guard might be sent out to prevent people from going in the water, and the jetty will be closed for walking and fishing, said lifeguard officer Gary Conwell.

Along with the high surf, Collins is expecting a strong riptide. The lifeguards don’t do their own surf forecasting but say that Surfline is often reliable.

“They seem to be right about a lot of things, but then again, it is the weather,” Conwell said.