Hurricane Katrina
With 
 likely to strike the city of New Orleans, its mayor, along with the governor of Louisiana, has officially enforced a mandatory evacuation for the city. All citizens, with the exception of a few individuals essential to the operation of a handful of organizations (such as hotels and the media), should immediately leave the city and head for higher ground. The mayor has stated that rising waters from the Category 5 storm are likely to overtake the city's system of levees, which are designed to prevent flooding in the city. Later predictions by NOAA downgraded the hurricane to a strong Category 4 at the time of landfall.
Mandatory evacuation declared in New Orleans, US