The North Shore is expected to get pounded by the biggest waves of the season tomorrow morning, with wave faces reaching the 20- to 30-foot level, according to the National Weather Service.

"We hope everybody will be safe," said forecaster Robert Ballard. "Please enjoy the show, but don't get too close. It will be a dangerous situation."

The weather service issued the high-surf advisory at 4 p.m. yesterday and urged people going to the North Shore to be wary while watching the show.

"It's so easy to be fooled," said Ballard. "People who are new to the Islands will go down to the beach and think they are in a safe spot, and all of a sudden they are in trouble. It's very deceptive."

North Shore waves can be deceptive even when they appear to be relatively calm, as they were on Oct. 18 when a visiting bodysurfer drowned off Sunset Beach.

Capt. Bodo Van Der Leeden of the city's Ocean Safety/Lifeguard Division said North Shore lifeguards will be posting "strong current" and "dangerous shore break" signs along the beaches.

They also may string yellow "hazard" tape at certain sites, such as Sharks Cove, Three Tables, or Chun's Reef, "where people try to get too close to the water," he said.

"If people see the yellow tape at the right of ways or at unguarded beaches, they should respect it. There's a danger of them getting swept off the ledges."

Van Der Leeden said when waves reach extreme heights predicted by the weather service, lifeguards take extra precautions.

"At that size it's possible that we could close a beach, depending on how the swell hits the shoreline," he said.

The North Shore's monster wave season officially rolled in Oct. 13, after the weather service issued its first high-surf advisory of the season. But that swell produced only 18- to 20-foot wave faces.

Weather service lead forecaster Victor Proton said the high surf will be preceded by high wind that should peak this afternoon with gusts to 40 mph.

"We have two components — a large storm system in the Gulf of Alaska that created a pretty good swell that's moving down, plus some brisk trade winds," said Proton.

While the winds will diminish as the day wears on, the waves will build up, with 8- to 12-foot faces this morning, reaching the 15- to 20-foot level by this afternoon, he said.

The waves should continue to build overnight, culminating in the largest waves arriving at around daybreak, he said.

Although the huge wave sets will stick around for a while tomorrow morning, they will rapidly diminish by tomorrow afternoon, he said.

Proton said the high-surf advisory also includes O'ahu's east shores, although those waves won't approach the heights of those along the North Shore.

North Shore wave faces will diminish to from 15 feet to 18 feet on Monday, and continue to drop to around 10 feet by Tuesday, said Proton.

Reach Will Hoover at whoover@honoluluadvertiser.com.