City beaches in the two boroughs — along with the National Park Service’s Jacob Riis Beach in the Rockaways — were closed to swimmers over fears of six-foot swells and “life-threatening rip currents,” City Hall announced late Friday.

“Our primary focus is keeping New Yorkers safe,” Mayor Adams said.

“New Yorkers should know the ocean is more powerful than you are, particularly this weekend.”

Lifeguards and parks officials will patrol to enforce the ban at the beaches, which all face the ocean.

“We strongly urge all New Yorkers not to risk their lives by ignoring this directive,” said NYC Parks Commissioner Sue Donoghue.

Ernesto rocked Bermuda with maximum sustained winds of 100 mph early Saturday and is forecast to travel northeast.

Although it will be 500 miles offshore the coast, it is still expected to still batter the region with powerful winds, towering waves and life-threatening rip currents.

Swells are expected to reach 6 feet in NYC and 9 feet on Long Island, according to the National Weather Service.

Wind gusts are forecast to reach 16 mph in the Big Apple.

The dangerous currents occur as increasing waves carry more water to the shore than can escape before the next wave arrives. The water then returns to the deeper areas through narrow channels, creating rip currents.

Swimmers stuck in one should not to fight it but either swim parallel to the shore or float until it subsides to avoid exhaustion, experts told AcuWeather.

Rip current warnings are also in effect along the Jersey Shore this weekend, where 30-mph winds are possible.

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Rip current warnings are also in effect along the Jersey Shore this weekend, where 30-mph winds are possible.