The third swell of the fledgling big-wave season rolled across the North Shore yesterday with average peak heights of 10 feet, but it was enough action to give Kapu Ping an early taste of the monster waves to come.

"It was a nice way to start the early winter," Ping, 19, of Wahiawa, said after emerging from the morning lineup at Waimea Bay. "It was a treat."

City lifeguards reported average wave heights of 6 to 10 feet along the North Shore and 3 to 5 feet on the Leeward Coast yesterday. By midday they had made three North Shore rescues.

They posted red warning flags all along the North Shore after forecasters issued a high-surf advisory and predicted waves with faces of 14 to 18 feet.

Lifeguards were also busy issuing 185 "preventative actions" along the North Shore by warning novice surfers and tourists to stay out of the water, as arriving sets of waves quickly reached inland, soaking unprepared visitors.

The west-northwest swell that arrived Monday night is expected to diminish today and linger through tomorrow and Friday, giving way to another north-northwest swell this weekend, the National Weather Service said.

The weather service continued yesterday to forecast rip currents and wave heights of 14 to 18 feet peaking last night. A high-surf advisory remains in effect until 6 a.m. today, with waves expected to reach 8 to 12 feet.

Kaz Sano videotaped North Shore surfers for his surf website, novusswell.com, and estimated that the biggest waves to hit Waimea yesterday morning about 6:30 a.m. had faces of 14 feet.

"It’s not like epic Waimea," Sano said.

But the waves were big enough to impress Jimbo Trusty, 21, who moved to Kaimuki last month from Virginia and drove out to the North Shore yesterday with a skimboard.

"Nothing gets this big on the East Coast, not even when there’s a hurricane," Trusty said.

Ping and his buddy Derek Wong, 20, of Kalihi could not agree on how big the waves were at Waimea yesterday. Ping estimated that the biggest waves were 10 feet high when measured "Hawaiian style" from the back, while Wong gave them a "solid 6 — Hawaiian style."

Wong and Ping then set off to check out the surf at Sunset Beach and Haleiwa before Wong needed to head back to town to attend an acting class at Kapiolani Community College.

Asked when he needed to be seated in class, Wong said, "10:45 or maybe 11."

Brittany Beaudoin-Canne chose to bring her sociology homework from Leeward Community College to the beach, where she lay on a blanket in the shade.

"I wanted to see the waves, but it’s kind of calmed down," Beaudoin-Canne said.

They were still big enough to bring out Alberto Maldonado, 48, of Kailua and his friend Dominic Perron, 23.

Perron had never surfed Waimea before yesterday and wanted to get a session in before he ships off to Navy Officer Candidate School on Oct. 23.

Even though monster waves never appeared yesterday, Maldonado was not disappointed.

Instead of working, Maldonado had another idea of what to do: "Surf all day," he said.