All New York City beaches will be closed to swimming starting Sunday, as tropical storm Hermine is expected to stall offshore and generate the most dangerous riptides New York City has seen in a decade or more, Mayor de Blasio announced at a press conference on Friday. The city is also preparing for coastal flooding and high winds, and residual downed trees and power lines.

"The number one concern is riptides right now," de Blasio said. "This is a very unusual situation. We could see some of the most intense riptides in literally ten or fifteen years. The phrase used by the National Weather Service is 'extremely dangerous' riptides… once the riptide grabs you, you can no get out in many, many cases."

"Do not even put your foot in the water on Sunday, and most likely several days after," he added. Beaches will be open to foot traffic, but beach goers can expect signage and warning flags at the water's edge, as well as Parks enforcement telling people in a "very direct and powerful way" not to go in.

New Yorkers can also anticipate possible bridge closures if winds exceed 40 miles per hour. The Department of Buildings has confirmed a no-work order, effective from 3:00 p.m. Saturday, to make sure that cranes are secured. Labor Day weekend events planned for non-coastal NYC neighborhoods, including the West Indian Day Parade and J'Ouvert, are not likely to be canceled as of Friday (though the Sanitation Department is dispatching extra workers to Eastern Parkway in case of fallen trees).

Last night Hermine became the first hurricane in eleven years to make landfall in Florida. And while the storm is expected to lose its tropical characteristics by late Saturday, the National Weather Service is predicting an "extratropical storm" over the western Atlantic. It's the offshore stall that has Mayor de Blasio particularly worried.

"The deeper fears of an ever-increasing storm have not been realized so far," he said. "What is different, is the phenomenon of this storm coming up the coast and stalling, really for four days, and that's really unusual."

"Be vigilant all the way to Wednesday, because this one's going to hang around for a while," he added.

Coastal areas are likely to experience flooding and heavy wind and rains Sunday and for four days following, according to the city: Coney Island and Gerritsen Beach in Brooklyn; The Rockaways, parts of Broad Channel, and Howard Beach in Queens; Midland Beach and Oakwood Beach in Staten Island; Throggs Neck and Edgewater in the Bronx.

There are no evacuation plans in effect as of Friday, but coastal New Yorkers are encouraged to prep go bags, and stock up on plywood, plastic sheeting and sandbags. Anything that could turn into a projectile in heavy winds should be secured. If winds get severe, "Get inside," de Blasio said. "Do not go driving, walking, or jogging."

Minutes before Mayor de Blasio's Hermine press conference, Governor Cuomo—not to be outdone—announced a "state emergency operations center" to launch Sunday at noon. This means the National Guard is on alert, with 100 soldiers and airmen, 45 vehicles (including high axel trucks stocked with blankets, lights, inflatable boats), and dump trucks and Bob Cats. There are also two emergency equipment stockpiles: in Brentwood, and at JFK airport. These include generators, light towers, water, ready-to-eat meals (97,104 standard, 19,200 Kosher), pumps and sandbags.

"While there is still uncertainty as to how far west the storm will track as it approaches New York State, we stand ready and prepared to respond with emergency equipment, supplies and personnel," Governor Cuomo stated.

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