Just when you thought it was safe to go back  in the water!

The Big Apple had deceptively perfect beach weather Friday with sunny highs in the low 80s — but many city swimming spots were closed due to dangerous conditions from Hurricane Erin’s aftermath.

Hotspots including Rockaway Beach, Coney Island and Manhattan Beach were shuttered Friday as massive waves and strong rip tides threatened suck away swimmers and surfers. State-run Long Island Beaches were closed just for swimming.

The storm could also put a damper on New Yorkers hoping to take a dip in the ocean over the weekend, when the weather will also be sunny and warm, said FOX Weather Meteorologist Cody Braud.

“Saturday will be a nice clear day but that doesn’t mean beaches will be safe,” said Braud said. “If you’re going to the beach, be on high alert. It’s not something you should take lightly.”

Beach-goers should check for high surf warnings, flags and possible closures on Saturday, when the rip tide threat is forecast as “high.”

The threat is expected to move into the moderate category by Sunday, he said.

“I would not assume the conditions are calm. It takes some time for the waters to reset after a storm like this,” Braud said.

While the city beaches were totally closed, Gov. Kathy Houchul on Friday banned swimming at state-run beaches on Long Island such as Jones Beach State Park and  Robert Moses State Park  due to “flooding and rough surf.”

“We must ensure that beachgoers aren’t put in harm’s way,” Governor Hochul said in a press release.

Gorge Gorman, a regional director of state parks, said officials will “analyze surf conditions” Saturday morning and then make the call about whether to close beaches.

“We’re looking at wave height, intensity of the wave, rip currents and strong undercurrents,” Gorman told The Post. “We’re looking at all of it.”

On Saturday, the weather is expected to be sunny in the low 80s in New York City, and  Sunday is forecast to be mostly clear and slightly hotter in the high 80s.

“It’s gonna be great —  there may not even be a cloud in the sky Saturday,” he said. “It was a very hot summer to start here and now we’re turning a page.”

Parts of the New Jersey shore were flooded Thursday night and Friday morning — prompting rescues, road closures and evacuations — as Hurricane Erin churned north.

More than 10 people were evacuated from storm-threatened homes in Atlantic City, where there were multiple beach rescues,  Scott Evans, the city’s emergency management coordinator, told the Philadelphia Inquirer.

Road closures were also reported in Burlington County and Cape May County, which put a flood warning in effect until 2 a.m. Saturday.

“While it existed, while it happened, [it] was less than we were fearing. Not surprisingly, coastal flooding was the big concern,” New Jersey Gov. Phil Murphy, who had declared a state of emergency, said at a press conference Friday. “Cape May County probably got hit the hardest.”

Coastal flood warnings, including on the New Jersey shore and parts of Long Island, are expected to be lifted Saturday, Braud said.