i think the key issue .. is what the authorities tell the residents of Manhatan. if the authorities tell people that the crisis is manageable, and most people decide to stay in their homes, then your character MIGHT make it out. Maybe.

But if there is widespread fear and panic, then your character has ZERO chance of evacuating ... because millions of other New Yorkers will jam all of the escape routes.

In my opinion, NO large US city, and probably no large city in the world, can be evacuated in a short period of time. Few people seem to realize this .. but it's a nasty reality.

Therefore ...

1. Your character must have an extremely unusual way to get out. for example, a person with a helicopter.

2. or alternatively, your character never makes it out, and fights a running battle for survival inside the city.

Either option is good for your story.

Please see ..

a. Real accounts of what happened when authorities tried to evacuate Houston before Hurricane Rita. It was a huge mess.

b. The scenes of evacuation in the movie "War Of The Worlds" with Tom Cruise.

c. What happened in New Orleans during Hurricane Katrina. Even to this day, there are residents of that city who are still bitter about the emergency response by the Government.

Human beings don't handle panic very well. it turns into very ugly behavior.

Your character is going to have to be an exceptional human being, or they really might not make it.

Good luck with your story.

Pete