One of the largest swells to hit the North Shore in 20 years backed off a bit Tuesday, giving many oceanfront properties a respite from erosion and a few surfers a shot at catching a wave.

And while the waves were expected to subside even more today, the next big swell is on its way — scheduled to arrive Thursday.

On Tuesday, following the unsurfable 55-foot-plus swells that pounded Waimea Bay on Monday, dozens of surfers were riding waves with faces up to 40 feet while workers on shore were assembling the stands for Thursday’s possible running of the Quiksilver in Memory of Eddie Aikau surfing contest.

Organizers have called a green alert for Thursday, meaning if conditions are right, the contest will go on. A decision whether to run it will be made at the beach that morning.

National Weather Service forecasters are predicting surf of 12 to 18 feet today but building tonight into Eddie-size, 40- to 50-foot waves Thursday.

Up and down the North Shore on Tuesday, owners of some of the homes that were hardest hit by Monday’s surf appeared to be preparing their properties for Thursday’s swell, in some cases shoring up property with sandbags.

A Kamehameha Highway home at Alligator Beach continued to teeter precariously after the property lost a seawall and part of its foundation Monday. A nearby home also lost its seawall, leaving it vulnerable.

A nearby oceanfront homeowner who spent a hectic day trying to help his neighbors Monday said he wasn’t going to clean up his property covered with sand because it was just going to happen again.

“We’ve got Thursday coming and I’m not happy about it,” he said, declining to give his name.

Another neighbor who lives up the hill, Paul Dunn, ventured to the beach Monday to pitch in.

“It was an exciting day in a sense,” Dunn said Tuesday. “But it was kind of sad along the coastline.”

Dunn, a 40-year resident of the North Shore, said he appreciated the city shutting down the road Monday — something that used to occur in the 1970s. The action helped homeowners who were trying to save their homes, allowing them to quickly retrieve supplies.

As for Thursday, he said, “I’m praying for all my neighbors.”

Two doors down, visitors Kyle Ferguson and Sam Butterfield from Edmonton, Alberta, said they felt safe and secure in their oceanfront rental, just steps away from the waves.

They said ocean spray reached their second-story lanai Monday, but it didn’t bother them. On the contrary, they said the sound of the surf was hypnotic, helping to put them to sleep.

“We’d rather have an avalanche of water than an avalanche of snow,” Butterfield said, enjoying an afternoon beer. “We’re fortunate to see something like that. It’s pretty neat.”

On Tuesday signs of Monday’s epic surf were everywhere — sand in parking lots and roadways. There was no shortage of yellow tape blocking off danger zones. Laniakea Beach was practically missing, with waves lapping up to the rocks that form the foundation of Kamehameha Highway.

At Waimea, Victor De Sousa and his family, from Toronto, were watching the surfers catch the big waves. They were on the beach while being careful to stay behind yellow tape keeping spectators well back of the surf’s run-up.

“That’s awesome,” he said, adding that the surfers are brave to challenge the mountains of water. “It’s stunning. The vista’s stunning. I absolutely see why they do it.”

Few surfers attempted the agitated monsters that came ashore Monday, but Tuesday was a different story. The city reported that lifeguards rescued 20 surfers and two bodysurfers at Waimea. There were also several broken boards and leashes.

At Chun’s Reef the city moved the lifeguard tower away from the surf. Lifeguards will patrol the beach on an ATV until it is safe to move the tower back near the shoreline, said Shayne Enright, spokeswoman for the Honolulu Emergency Services Department.

At Sharks Cove, Adam Fields of the Gold Coast of Queensland, Australia, was photographing the waves crashing on the rocks.

“They’re amazing,” he said. “We never see anything like it.”

Bryan Suratt, owner of Sunset Suratt Surf Academy, said Monday’s monster swell prompted him to cancel all of his surfing classes. But Tuesday he was back at it, teaching at the sandbar in Haleiwa Harbor, a relatively protected surf spot known as Chocolates.

“Today was perfect,” said Suratt, who coaches pro surfer Makua Rothman and teenage stand-up surfing champion Izzi Gomez. “Yesterday was so bad. Others were out there teaching, and I was thinking, ‘You gotta be kidding me.’ It was crazy.”