It will happen quickly, forecasters say.

Surf conditions around the Islands, including O'ahu's famous surf mecca on the North Shore, will likely remain relatively stable this morning. By this afternoon, they will steadily accelerate to the biggest waves of the season.

"It looks like the waves will be building throughout the afternoon, peaking at 25- to 35-foot faces," said National Weather Service lead forecaster Tom Birchard. "The heights might dip a little on Thursday, but come back up again on Friday to 25 to 35 feet again."

But the surf — while big — might not be good for wave riding due to west winds that aren't conducive to North Shore surfing.

And potentially powerful, damaging winds are expected tomorrow and Friday

But as for the big waves, the city's Ocean Safety Division said it's prepared for whatever comes.

"We know how to do the North Shore thing," said Jim Howe, chief of operations for the Ocean Safety Division of the Honolulu Emergency Services Department. "We have been doing this for a long time.

"Our system is designed to help folks understand the extreme hazard of the high surf situation. And we will be doing all of the things we do to help everybody stay safe."

Bryan Cheplic, spokesman for Ocean Safety and Emergency Medical Services, said it is vital for people to understand what those hazards are.

"We're really asking people to check with the lifeguards before going into the water," said Cheplic, who said that includes experienced swimmers. "If you're inexperienced, avoid going into the ocean.

"We're also asking for the public's cooperation in heeding all warning signs."

Similar caution was being advised on Kaua'i.

Kaua'i Civil Defense has warned coastal residents and businesses of the impending high surf, said director Mark Marshall.

Kaua'i lifeguards expect to discourage any swimming on north shore beaches or at Kekaha on the island's west side today, said Kalani Vierra, water safety supervising officer for Kaua'i's Ocean Safety Bureau.

Mark Cunningham, surfer and retired O'ahu North Shore lifeguard said he will not be going into the water today.

"Heck no — I don't go anywhere near waves that big," Cunningham said. "I'm very much a spectator."

Cunningham predicted that even seasoned surfers will be joining him on the sidelines.

"From the forecasts that I've looked at, we've got pretty darn strong west winds blowing," he said. "And that is just not favorable surfing conditions for the North Shore."

NOAA surf forecaster Pat Caldwell, who said the big waves should last from this afternoon all the way through the weekend, agreed with Cunningham's analysis.

"It doesn't look like the timing is good for the surf conditions on the North Shore with the wind issue," he said.

It was the wind forecast for tomorrow and Friday that most bothered those monitoring Mother Nature.

"There's more to our forecast than just a high surf warning," Birchard said. "We've issued a special weather statement. We're expecting gusting southwest winds on Thursday and Friday. The potential for damaging wind gusts exists, especially in those areas where the winds accelerate down the slopes."

Howe said: "They're talking gale force winds with gusts of up to 60 miles per hour. These southwesterlies funnel down through the valleys on the Windward side. And they blow like a hurricane."

Boaters and kayakers on the Windward Coast who are used to gentle trades moving toward the shoreline can be caught off guard by these rare strong winds blowing out to sea, Howe said.

"The one I remember when this happened was three people got a little inflatable at Kualoa, just to take a little paddle out to Chinaman's Hat — never to be seen again."