"The good news is that [a hurricane] would have to make something of a bank shot, as Hurricane Agnes did in 1972, in order to pass directly over New York City."

"It is intrinsically fairly hard for a storm to make landfall upon New York City itself rather than somewhere else along the Atlantic," explains Nate Silver.

A considerably more likely scenario is that a hurricane-strength storm would come ashore on central Long Island. That would still be extremely bad: a weak Category 2 storm with an eye that passed about 50 miles from Manhattan would result in about $10 billion in damage, according to the model.

Although highly unlikely to be experienced in the case of Hurricane Irene, it is theoretically possible that an even stronger storm might hit the city at some point in the future. A Category 3 hurricane, one with wind speeds of 111 miles per hour or higher, could plausibly produce an economic impact in excess of $100 billion if its eye were to pass directly over Manhattan, according to the model. A stronger Category 3 storm, passing immediately over Manhattan, could rival or exceed the roughly $235 billion in economic damage estimated to have been caused by the Japanese earthquake and tsunami.

And more than a Category 3? Directly hitting NYC? It's never happened. "[I]in recorded history, no storm has made landfall in the Northeastern United States while stronger than a Category 3." But if it did — and Silver says maybe with global warming it might — the economic impact would hit the trillions.

Keep in mind that New York’s annual gross domestic product is estimated to be about $1.4 trillion — about one-tenth of the nation’s gross domestic product — so if much of the city were to become dysfunctional for months or more, the damage to the global and domestic economies would be almost incalculable. The property value of New York City real estate, meanwhile, is estimated to be about $800 billion, and property damage represents only a portion of the overall economic loss that might be incurred from a catastrophic hurricane.

Where would the people go? What would happen to them?