Escape Route #1: Bike out
What to do: Pedal uptown on the Western side of the island toward the George Washington Bridge and head across one of the pedestrian walkways. The entrance to the South sidewalk is at 177th Street and Cabrini Boulevard. If you take the North sidewalk, closed to pedestrians in 2008, at near the corner of West 179th Street and Cabrini Boulevard, you'll have to carry the bike up flights of stairs, but you'll deal with fewer panicky citizens.
If the GWB is inaccessible, bike up to the northernmost end of Manhattan, and cross the Broadway Bridge into Marble Hill and on toward upstate New York. It's a longer ride, but also likely safer not to have to deal with the potential high winds on the bridge.
Likelihood of success: Strong if you leave early tomorrow. Not-so-strong if you don't have an end destination you're biking to. Given you won't have any safety from the storm in your Speedo bike gear, this is really only suggested if, say, your car breaks down in the city, Bloomberg has shut down mass transit and you need to get to your home in Ryebrook. Douche-y financial district I-bankers, I'm looking at you.
Escape Route #2: Buy/procure a scooter
What to do: Slap down a credit card (if the approval network connection is still up and running), or otherwise procure a Vespa scooter from Vespa Soho and make a mad, lane-splitting dash uptown to Westchester County, using the same network of roads and bridges you'd use for the bike path.
Likelihood of success: Strong. But again, only if you have an end destination in mind. Vespas don't provide the best help when you're exposed to the elements. Also, they're not allowed on the George Washington Bridge. At all.
Escape Route #3: Swim for it
What to do: Hopefully you've been working out, because swimming is hard work, especially if you're aiming to swim almost a mile to Hoboken. But people have swam the span from nearby Weehawken on a whim, so you can too. Although not a problem now, if your escape from New York is occurring in the winter, your first stop should be to liberate a wetsuit from the SBR Triathlon Store on 58th St.
Likelihood of success: Slim. Riptides are already a problem in New York's waterways even by early tomorrow morning.
Escape Route #4: Commandeer a kayak
What to do: If you can't swim, get a personal paddlecraft — either a kayak, or a stand-up paddleboard (SUP) from Manhattan Kayak and start paddling across the mighty Hudson. (This guy does it every day.)
Likelihood of success: With a kayak, a little bit better than swimming. Stand up paddleboard? Not a chance. The winds and water will already likely be whipping up something fierce.
Escape Route #5: Get to the 79th Street Boat Basin
What to do: Naturally, this is where most of the city's private-owned pleasure boats are, and where you'll have the greatest chance of finding someone willing to sail or motor you across the river. Make sure to bring something to trade on, like provisions, foul-weather gear or batteries.
Likelihood of success: A quick sprint across the Hudson might be doable depending on what time of day you make the voyage tomorrow. The earlier the better. I'd say survivability's pretty good with this one.
Escape Route #6: Sneak through the North River Tunnel
What to do: The 14,575-foot-long North River Tunnels, completed in 1910, originally ran trains from the Pennsylvania Railroad to reach Manhattan. Now they carry Amtrak's Northeast Corridor and New Jersey Transit trains between Weehawken, New Jersey and New York's Penn Station. There are two tubes; trains ordinarily travel west (to New Jersey) through the north tube and east (to Manhattan) through the south. The tunnel openings here in Manhattan is at the east edge of 10th Avenue at 32nd St in Manhattan, hidden beneath the big tan building on the east side of 10th Avenue. Just watch out for that third rail and the overhead lines. They're positively electrifying.
Likelihood of success: This route's really dangerous. With the electric power running through the third rail and overhead lines, not to mention the likelihood of plague-carrying rats making their own Mickey Mouse Plissken dash for freedom, this one's not the smartest idea. Also, once the rain starts you don't want to be anywhere near a tunnel for fear of serious flooding.
Escape Route #7: Hang glide off a building
What to do: Considering a hang glider's typical 12:1 glide ratio (a hang glider can travel 12 meters forward in smooth air for every 1 meter of altitude lost), you'll have to get yourself and your gear to the top of a 400-foot tall building to make the one mile (1,609 meters) crossing. You'll have plenty of choices; among the tallest buildings in Manhattan, number 90 (Times Square Plaza, at 11 Times Square) is 600 feet tall. You'll also need to fabricate some sort of ramp, so you can get the whole glider, tail and all, clear of the building's edge, so you don't nosedive into the street.
Likelihood of success: Ha. Not a chance in hell. Don't even think of trying this one for Hurricane Irene.