Lifeguards noticed an unusual surf pattern at Waimea Bay that featured long intervals of calm, glassy water interrupted by 8- to 12-foot waves, said Jim Howe, chief of operations for the city's Ocean Safety Division.

"The ocean becomes completely flat, like a swimming pool, and everyone jumps into the water," Howe said. "Then all of a sudden, big waves show up, and consequently there were seven rescues at Waimea Bay."

One of the swimmers, a 48-year-old man, complained of back pain and was airlifted to The Queen's Medical Center as a precaution, said North Shore lifeguard Lt. John Hoogsteden.

Most of the seven people rescued were tourists, Hoogsteden said.

Howe said such surf conditions are normally are seen early in the winter surf season in September or October. Sometimes the unusual conditions don't occur at all, Howe said. Lifeguards will post warning signs tomorrow if dangerous conditions persist, Howe said.

Waves are expected in the 6- to 10-foot range tomorrow on the North Shore, and Hoogsteden said lifeguards want beachgoers to be aware of conditions as they make plans for the three-day President's Day weekend.

"When people come to the beach they should check with a lifeguard," Hoogsteden said. "That's the best advice we can give."