Beachgoers are being urged to stay out of the water because of surf that could reach 14 feet this week along the south shores of all Islands.

The National Weather Service yesterday issued a high-surf advisory for south-facing shores beginning today and lasting through Friday. The surf is expected to begin rising today and reach heights of 8 feet by 2 p.m. today.

The surf will continue to build, and by tomorrow afternoon waves of 10 to 14 feet are expected to begin pounding normally tranquil south-shore beaches. The high surf will continue Thursday and begin to diminish on Friday, said Jeff Powell, National Weather Service lead forecaster.

Surf heights are measured on the face, or front, of the waves.

Powell said a storm in the southern hemisphere generated the surf that's just reaching the Islands. He said high surf on the south shores is "not unheard of" during the summer months, while big surf during the winter normally hits the north shores.

Powell said large surf can cause property damage, but the main concern is that people stay away from the water.

"The usual hazards with high surf, of course, is you've got big waves crashing down. You've also got undertow and rip currents that could cause problems," he said.

Waikiki lifeguard Tony Ho said the city Ocean Safety Division will likely increase staffing along the south shores to prepare for the high surf. He said signs will be posted along the beaches and that lifeguards will be using megaphones to warn beachgoers.

"You hope and pray that they heed what we say or recommend," Ho said. "It's going to be tough, but we've had a couple, and we've weathered the storm."

Reach Curtis Lum at culum@honoluluadvertiser.com.