Ocean safety officials are preparing for a massive incoming swell.
Surf is high now, and expected to get even bigger over the next several days.
Waves could get as high as 40 feet and erosion continues to be a concern.
Warning level surf should reach Kauai by early Thursday afternoon, spread down the island chain, and peak Thursday night.
Surf will then gradually decline Friday, staying near advisory levels before an extremely large, long-period northwest swell builds Friday night and peaks Saturday evening.
The city Ocean Safety and Lifeguard Services Division says it will be fully staffed and lifeguards will start their shifts an hour earlier.
Twenty-eight lifeguards will be on hand this weekend, and rescue watercraft will be on patrol.
Despite warnings, beach goers are still taking their chances.
On Thursday, ocean safety officials say a visitor from Canada got hurt at Waimea Bay and was rushed to the hospital in serious condition.
This is the third serious accident this week. Professional surfer Dusty Payne is still recovering after a major wipeout, and on the same day, another visitor died at Rocky Point.
Lifeguards are reminding the public that the water is unpredictable.
"It can be quite a long stressful day for lifeguards. Everyone out here in District 3 is a seasoned veteran. This is what we prepare for and train for," said Lt. Kerry Atwood. "If you are planning on coming to North Shore, make it a no-swim day, no recreational swimming. We want to warn everyone, it's important to stay off wet rocks, sand. Abide warning signs. Don't cross caution tape, and listen to lifeguards. Carelessness costs lives."
A high surf warning is in effect until 6 a.m. Friday for north- and west-facing shores of Niihau, Kauai, Oahu, and Molokai, and north-facing shores of Maui.
A high surf advisory is in effect for north-facing shores of Hawaii island.