Thursday morning on the Long Island coast sure didn’t look like a surfer’s paradise. It was chilly, misty and gray, and the sea looked fussy. Pedestrians along the boardwalk huddled in windbreakers and sweatshirts.

Then, a sudden movement on the ocean: Among the dozens of figures in neoprene suits in the choppy water, bobbing up and down, a lone surfer erupted in a fierce paddle. He popped up to his feet, dropped down the face of what looked to be an eight-foot wave — huge for an August day on Long Island — slid into the barrel and was spit out triumphantly.

This is the kind of wave that New York surfers dream of catching all year long.

As Hurricane Erin moved up the East Coast, surfers in and around New York City, who are known to put on hooded wet suits in February to chase decent waves, are enjoying the rarity of the best waves of the season on a summer day.

Before most Long Islanders had even had their coffee, there were more than 50 surfers in the water off Long Beach.

“This is what they get excited for; this is what amps them up,” said Adrien Gallo, a surfer dad armed with camera gear. He was there with his wife, Kyle Ferrara, watching their three children, Charlie, 14, Palmer, 13, and Wilds, 11, deftly surf waves most adults shouldn’t attempt.

Hurricane season usually brings big waves to New York, but rarely are they as surfable as the ones breaking this week on Long Island and the beaches of New York City.

Hurricane Erin is the fifth named storm to form in the Atlantic this year. There has been damage from the storm already: Some central roads in the Outer Banks of North Carolina were impassable on Thursday morning, and the National Hurricane Center said that the storm surge presented a “life-threatening situation” in Duck, N.C. The Hurricane Center warned that Erin would continue to produce dangerous surf and rip currents on beaches from the Bahamas to Canada for the next several days.

Swimming was banned on beaches in New Jersey and Delaware on Tuesday, and beaches in New York City were closed on Wednesday and Thursday. An exception was made for surfing.

“The rule is: Only surfers allowed,” said Kiante Liaping, 31, a security guard for the city’s parks department who was stationed at Rockaway Beach on Wednesday. The water was high but messy, with big waves and little ones appearing by surprise and crashing at random. In the break zone, about a dozen surfers bobbed on their boards. A few managed short rides before the wind and chop blew them off.

The only time Mr. Liaping blew his whistle was when a photographer wandered too deep trying to get a shot of the action in the waves. “The surfers know what they’re doing,” he said.

Even the most experienced surfers in the Rockaways agreed that this week’s waves were something special. Sofia Grunwald is a surf instructor at her home in Chile. After a visit to New York, she had planned to fly to El Salvador in mid-August for some good surfing.

When she heard about Hurricane Erin, she postponed her flight and waited more than a week for the predicted great waves to arrive. On Wednesday morning, she climbed the stairs to the boardwalk at Beach 94th Street in the Rockaways, her surfboard tucked under her right arm.

The moment she saw the water, she smiled and started to run. She caught the first wave she met, riding it all the way into the sandy shallows, laughing and pumping her fist in the air.

“When I was here two weeks ago, it was flat,” said Ms. Grunwald, 27. “So I just waited. This is pretty fun.”

Around the Rockaways this week, people in the surfing community were divided over how much experience was necessary to tackle these waves. Even as the nearby beach filled with surfers on Wednesday, Boarders Surf Shop, which rents surfboards on Beach 92nd Street, was empty. Most beginners were put off by the rain, wind and tall waves, said Paige Stathis, whose grandfather opened the shop in 2004.

“Once the waves get to four or five feet, we stop renting the big foam boards,” Ms. Stathis said.

A mile away, at Breakwater Surf Co., the manager, Anthony Ayala, was less concerned. He had rented out five boards that day, he said, after sussing out the skill level of each surfer and spending nearly an hour surfing the breaks himself.

With the storm predicted to intensify on Thursday, however, Mr. Ayala said he planned to suspend all rentals moving forward.

“We rented today because the waves are big but mushy, so they’re not so powerful,” he said. “Tomorrow? Probably no. If the forecasts are right, it’ll be too strong for beginners.”

That was definitely the case on Long Beach on Thursday morning. But 11-year-old Wilds was no beginner. Nearly the moment he hit the sand, he unzipped his board bag, flung his sweatshirt off and sprinted to the water. His board bag was almost lost to the wind; a few spectators chased it down as the young surfer took his first strokes in the ocean.

His sisters were still waxing their boards as he raced back to shore, his short board under his arm and his dyed blonde hair spiked skyward. He couldn’t get the words out quickly enough.

“It’s so good out there, Dad!” he exclaimed. “It’s like, a set showed up and we all were like” — he let out an expletive that made his father flinch.

“Dude, you can’t swear, you’re 11,” Mr. Gallo responded, laughing. The Gallo children were joined by surfers of all ages, but all seemed incredibly experienced.

The currents were strong, multiple surfers said, and navigating the tides was more difficult than actually surfing the waves. “It’s big and fun,” Charlie, Wilds’s older sister, said, “but it’s not safe for people that can’t surf.”

Even by early morning, waves were building to heights of more than 10 feet. By the evening, they were projected to reach close to 20 feet, conditions that would be considered “a once in a decade” occurrence, said Will Skudin, the co-founder of Skudin Surf, a surf school with locations in New York and New Jersey.

Mr. Skudin, an accomplished big wave surfer in his own right, shut down his lessons and camps until the storm passed. (The waves were expected to peak in size overnight into Friday and return to average heights by Saturday.)

“You can’t teach people how to surf in a hurricane,” he said.

Aidan Lyons didn’t ask anyone for instructions. He simply arrived at Rockaway Beach on Wednesday morning, rented a foam longboard and jumped into the water. It was his first day of surfing in his life. What ensued was several hours of trying to stand up, and failing.

“It isn’t very smart, I guess,” Mr. Lyons, a 21-year-old musician who lives in Bushwick, said of learning to surf in the outer reaches of a hurricane. “But I love it.”