All residents of New York City who live in low-lying areas must evacuate their neighborhoods by 5 p.m. ET Saturday because Hurricane Irene is headed their way, Mayor Michael Bloomberg just announced.
Reuters says an estimated 250,000 people are affected. The city is opening shelters. Bloomberg said this has never been done before.
There's a pdf of "New York City Hurricane Evacuation Zones" posted here. And there is a page where you can find out if your address is in one of the zones online here.
In addition, the city is shutting down its transportation system on Saturday.