From the NYC.GOV Severe Weather site:
Mandatory Evacuation Issued for NYC Coastal Areas
Due to the approach of Hurricane Irene, the City has issued a mandatory evacuation order for New Yorkers who live in the low-lying Zone “A” coastal areas across all five boroughs and the Rockaways. These areas include: Coney Island, Manhattan Beach, Far Rockaway, Beach Channel, South Beach, Midland Beach, and Battery Park City. People should be out of these areas by 5 pm on Saturday.
Residents who live in Zone A are strongly encouraged to stay with friends or family outside an evacuation zone. Evacuation Centers are open for residents who have no alternative shelter.
MTA service including subways, buses, and railroads will begin to shut down at noon tomorrow, so please prepare to evacuate immediately.