Only 700 water pumps keep the tunnels dry, pumping 13 million gallons of water out of the subway on a daily basis. But the pumps may not be able to handle the amount of water that could flood the tunnels during the storm, according to the hydraulics team head of New York City's Metropolitan Transportation Authority.
High rise residents who live in Manhattan skyscrapers are warned to stay away from windows. The wind picks up above the 10th story and the risk of breaking glass is greater the higher you go.
Once winds reach 60 miles per hour, the city's beaches, the bridges in and out of Manhattan, and major highways will be closed.
In New Jersey, Atlantic City has closed its casinos, and New Jersey Gov. Chris Christie ordered everyone off the beach in his trademark blunt style.
"Get the hell off the beach in Asbury Park and get out. You're done. You've maximized your tan," Christie said. "Get off the beach."
Columbia University and New York University, two of New York City's largest private colleges, have rescheduled their freshmen move-in day from Sunday to Monday.
"Doing it in the middle of a hurricane would probably not be the best experience," Bloomberg said.
For more on how Hurricane Irene is affecting New York and the surrounding tri-state area, go to ABC News affiliate WABC-TV.