Unusually high surf will batter south shores through tonight, bringing wave heights between 10 and 15 feet and keeping lifeguards from Ala Moana to Hanauma Bay on alert.

A National Weather Service high surf warning for south-facing shores posted yesterday said the swell would generate "battering waves" and "deadly rip currents." Swimmers and novice surfers were urged to stay out of the water or evaluate conditions before going in.

Weather service meteorologist John Bravender said the swell peaked late yesterday afternoon, and would slowly subside through tomorrow. The big waves will likely not affect homes along the water, but officials are warning boaters about possible harbor surges and say there is also the possibility of severe beach erosion.

South shore swells this late in the year are rare, Bravender said.

The last big autumn swell was two years ago.

Though there were no serious injuries, yesterday's waves kept lifeguards busy. At Waikiki, lifeguards helped more than 100 swimmers and 200 surfers back to shore after they got into trouble.

Lifeguards say they are hoping for more wet weather today to keep many out of the water. "The ocean is very ugly right now," which means most are choosing to steer clear of the water, said Jim Howe, operations chief for the city Ocean Safety and Lifeguard Division. Still, plenty of surfers are expected to come out today.

"We are prepared for whatever happens," Howe said, adding officials will survey the waves today to see whether more lifeguards should be put on beaches along the south shore.

As the surf rose yesterday, surfers clamored to sample the waves — despite the wet weather. "It is actually a pretty good swell," said Ernesto Valentin, of Kapahulu.

Valentin was in waters off Diamond Head by 9 a.m., and left around noon.

By then, a steady stream of surfers had turned out to check out the surf. At Diamond Head, about two dozen people were in the water, making the most of the waves through choppy conditions and intermittent heavy rain.

Sheldon Fujishige, 50, was smiling as he prepared to get into the water.

The Kaimuki resident, who often surfs at Diamond Head, said it was about time the south shores saw some big waves after a long summer of disappointing swells.

"It's a welcome sight," he said, with a laugh.

Christine McNulty and Cyrus Ikegami surfed Diamond Head yesterday morning, and said the waves were very choppy at first, but got better as the day wore on.

"It wasn't perfect," Ikegami said.

The high surf warning extends to all Islands through 6 p.m. today.

The weather service said the swell was generated by a storm over New Zealand about a week ago.

Reach Mary Vorsino at mvorsino@honoluluadvertiser.com.