A powerful nor’easter pummeled Long Island throughout Saturday, forcing an emergency travel ban, flooding some coastal areas and burying the region under wind-whipped snowdrifts.

A blizzard warning remained in effect until 7 a.m. Sunday, when Gov. Andrew M. Cuomo planned to reopen highways and local roads. Forecasts called for an end to snow showers in the morning, followed by welcome sunshine and above-freezing temperatures by midday.

“This has been a storm worse than predicted,” Suffolk County Executive Steve Bellone said late Saturday afternoon. “It is a really significant storm.”

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The storm dropped more than 20 inches of snow in areas of Long Island and New York City, and packed sustained winds of 20 to 40 mph with gusts up to 65 mph.

Despite the ferocity of the storm, power outages on the Island were relatively modest and there were few major traffic wrecks reported in Suffolk and Nassau counties.

Snowfall was expected to slacken after midnight, said Faye Barthold, meteorologist with the National Weather Service in Upton.

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Lingering winds at 10 to 15 mph could blow drifts around Sunday morning, creating the illusion of more snowfall, but “by the time people wake up . . . the snow should have moved out,” she said.

With snow still falling at about 8 p.m. Saturday, there were 23.7 inches in Islip and 22.9 inches in Wantagh, according to the Weather Service.

Long Island MacArthur Airport in Islip reported 22 inches at 7 p.m. The record of 27.8 inches was set in February 2013. The Weather Service began keeping records there in 1984.

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Cuomo declared a state of emergency for Long Island, New York City and downstate counties Saturday morning, including a ban on travel on all state and local roads on Long Island and in the city.

Gary Puetzer, 54, a heavy-equipment operator for the city of Glen Cove, said the storm is among the most treacherous he’s experienced in 15 years of driving snowplows.

“As far as visibility, it’s the worst I’ve ever seen,” he said. “This morning, I couldn’t see anything.”

The travel ban was largely successful, local officials said, with motorists mostly heeding the call to stay off the roads.

Five area storm-related deaths were reported by police, with two on Long Island.

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A 94-year-old Smithtown man died after being found collapsed outside at about noon next to a snowblower. The other victim was a 61-year-old man who went into cardiac arrest while shoveling snow in West Hempstead at 4 p.m.

The other three deaths were in New York City and linked to shoveling snow, the NYPD said.

The Long Island Rail Road, exterior subway lines in New York and bus service in the region also halted service.

Cuomo said Saturday night that he planned to lift the travel ban at 7 a.m. Sunday, and added he would make a decision on mass transit, including the LIRR, at 6 a.m.

During the storm, the highest snowfall rate came between 7 and 8 a.m. in Islip, which saw 3 inches per hour come down, according to Barthold. Rates of 1 to 2 inches per hour in other areas were common, she said.

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Wind gusts throughout the storm were above 35 mph, although it was still too early Saturday night to officially declare the storm a blizzard, Barthold said.

There must be sustained or frequent gusts above 35 mph for three or more hours, with “considerable falling and/or blowing snow,” for a blizzard to be declared, according to the agency.

“Some areas of Long Island will approach totals that we had in the blizzard of 2015,” said News 12 Long Island meteorologist Rich Hoffman.

The Weather Service said a snow band that tracked north with a developing low brought the heaviest precipitation to the area. The snow also started falling earlier than originally anticipated, boosting the totals.

Late Saturday night, local officials were bracing for the storm’s final punch: a potential for additional coastal flooding during high tide.

The combination of the storm’s fury and a full moon caused flooding along the Atlantic Ocean shorelines, with high winds driving higher-than-usual tides and swells onto land, meteorologists said.

Nassau County Executive Edward Mangano had issued a call for residents in flood-prone areas to leave the area before the travel ban took effect Saturday afternoon.

John Murray, meteorologist with the Weather Service in Upton, said it was likely Saturday night’s flooding would be the same minor-to-moderate coastal flooding that occurred Saturday morning.

On Saturday, police closed Asharoken Avenue, the only access road in the Village of Asharoken, after water washed over it — a common occurrence during storms, according to Huntington Town spokesman A.J. Carter.

Parts of Bayville Road and Bayville Avenue were closed in the afternoon, Bayville Mayor Paul Rupp said.

“There’s flooding on the street,” he said. “We’re waiting for the tide to drain it out.”

Flooding was as deep as 6 inches, although there were no reports of damage, Rupp said just before 1 p.m.

“The most dangerous hit from Mother Nature is the flooding,” Cuomo said at a news conference in Melville Saturday afternoon.

Long Island towns had difficulty keeping pace with the heavy snowfall.

Huntington Town Highway Superintendent Peter Gunther said whiteout conditions and drifting snow proved a challenge to road crews.

Strong winds were blowing snow back onto already plowed streets, forcing workers to repeatedly clear the same roads, he said.

“Definitely a problem with the drifting and stuff, and just trying to plow with the whiteout conditions,” Gunther said Saturday night. “You know how the wipers are. They get iced, it presents a visibility problem. You can’t go as fast as you like. You really have to go slow.”

Gilbert Hanse, director of emergency management for the Town of Babylon, said while the main roads were mostly passable, smaller cars with a lower clearance were getting stuck.

“That’s the problem — there’s a lot of snow, and people think they can drive their Prius out here, and it doesn’t work,” he said.

There were 62 motor-vehicle crashes in Suffolk — five of those with relatively minor injuries, Deputy Police Commissioner Tim Sini said Saturday evening.

Nassau police reported 74 crashes by Saturday afternoon, with icy roads and high winds causing “minor accidents and spinouts.”

Hospitals on Long Island saw some snow-related injuries, including Stony Brook University Hospital, where a man was treated for injuries after he fell off a ladder while trying to stormproof his house.

“We set up for it but fortunately, I think after all the bad weather we’ve had . . . people have really started to listen to news advisories, and we haven’t had as much bad stuff,” said Dr. James A. Vosswinkel, the hospital’s chief of trauma surgery.

Most flights out of Kennedy and LaGuardia airports were canceled, Port Authority executive director Patrick Foye said. Southwest Airlines canceled its flights at MacArthur until Monday morning, while American Airlines canceled its flights until 5:59 p.m. Sunday.

In New York City, all Broadway shows were canceled Saturday, while Mayor Bill de Blasio urged stores and restaurants to close and send employees home lest they get stranded in the snow.

He also requested that anyone traveling to the city earlier in the day return home.

“Anybody who’s come into the city from the suburbs should turn around and go back,” de Blasio said at a news conference.

Thousands of people and trucks, from the National Guard to Suffolk police in high-axle vehicles, waited in the wings to zoom to any trouble spots, authorities said. PSEG Long Island faced sporadic outages throughout the storm but largely avoided the widespread outages feared.

The company will have about 340 off-Island workers joining about 1,000 PSEG field workers and on-Island contractors to respond to any outages, he said.

Power outages were relatively modest, peaking in the morning with nearly 14,000 customers affected.

The Coast Guard, noting that seas could swell as high as 18 feet, urged boaters to seek safe harbor until the storm passes. A high-surf advisory was in effect until 6 p.m. Sunday.