The second large swell on the North Shore this week began building Wednesday afternoon, ushering in hope that the surf would be good enough to run the Quiksilver in Memory of Eddie Aikau surf contest and bringing worry to residents whose homes were being undermined by erosion.

The National Weather Service forecast calls for surf of 40 to 50 feet on the north shores from Niihau to Maui and surf about half as large on west Oahu and Molokai and on the north shore of Hawaii island. A high surf warning was set to expire at 6 a.m. Friday.

The weather service warned of possible impacts including ocean surges sweeping over beaches and roadways as well as damage to coastal properties. Also, large waves could affect harbor entrances and damage boats, ramps, piers and docks.

Organizers of the Eddie surf contest were cautiously optimistic that the competition will go today. They said Wednesday afternoon that they expected to have a better idea after later reviewing off-shore buoy reports. They will make the final call at about 6 a.m.

At a news conference Wednesday in Honolulu, previous Eddie winner Keone Downing said, “There was a reason there was a saying: ‘The bay calls the day.’” He added, “When we show up in the morning and we check our buoy reports … it gives us a real good idea. But until those solid, concrete pieces come in place, it’s always up in the air.”

Officials were making preparations to handle an anticipated turnout of thousands of spectators for the event at Waimea Bay, which could get underway at 8 a.m. Additional police, funded by Quiksilver, will deploy for the event, Honolulu Mayor Kirk Caldwell said.

Barriers and signs pertaining to parking restrictions along Kamehameha Highway near Waimea Bay were expected to be in place starting at 10 p.m. Wednesday.

The city has added eight Route 52 bus departures this morning, with four leaving from Ala Moana Center on Kona Street and four departing from Alapai Transit Center.

The added Ala Moana Center departures are set for 5 a.m., 5:30 a.m., 5:45 a.m. and 6:20 a.m. The added departures from Alapai Transit Center: 5:10 a.m., 5:40 a.m., 5:55 a.m. and 6:30 a.m.

In addition, the city has added a 5:15 a.m. departure from Ala Moana Center for Route 55, which travels to Haleiwa via Kaneohe.

Some 15,000 to 18,000 people arrived at Waimea Bay two weeks ago when the Eddie almost went, event director Glen Moncata said Wednesday. Some of those spectators were able to park along Kamehameha Highway despite the parking restrictions — and many were ticketed.

This time around, parking barriers will make parking on the side of the highway difficult to impossible, Honolulu Police Department Maj. Kerry Inouye said.

City lifeguards will work longer hours watching the shores today, from 7:30 a.m. to 6:30 p.m., although city officials strongly advised that the public stay out of North Shore waters during the swell.

As preparations were being made to the judging stage at Waimea Bay, beachgoers were excited to see the surf already coming up.

For Dennis Lippert of Makakilo, today’s event marks his second attempt to catch the Eddie. The first was two weeks ago when the contest was called off because the required big waves failed to materialize.

On Wednesday, he arrived at Waimea Bay with his wife and two daughters about 1:30 p.m. to get a parking spot close to the bay. His family planned to stay in the car overnight and be at the gate when it opens at 5 a.m., at which time, he said, they will grab their chairs and run to the beach to secure a coveted spot.

North Shore surfer Sunny Garcia, who is still recovering from a broken bone in his right forearm — the result of a December mountain biking accident — said he plans to surf in the Eddie if it is held. He said the waves have to be worthy of honoring Aikau, the legendary waterman after which the event was named.

“If it’s on, we’ll surf,” Garcia said. “It’s the Eddie. It’s the most prestigious big-wave event in the world.”

He said the Eddie also serves as an opportunity for big-wave surfers to meet or reunite after not seeing one another for long stretches.

Meanwhile, dozens of volunteers gathered at a house on Farrington Highway near Alligator Rock throughout the afternoon Wednesday to make emergency preparations to save a home on the verge of collapsing before the big surf came in.

Ralph Gray said that about 20 feet of his neighbor’s home was extended over a sinkhole carved out by the ocean.

The surf undermined a rock wall that was supposed to protect the home from erosion and part of the wall collapsed recently, allowing the ocean to wash away part of the ground. He said support posts were added beneath the home, and volunteers were stopping by to fill sandbags to shore up the foundation.

“It’s bad,” said Jarvis Gray, another neighbor helping the homeowner. “I see the worst,” he said, adding that the house could fall today. “You can’t stop the ocean.”