This article covers the details of the Preparations for Hurricane Katrina, a major category 5 hurricane that devastated parts of Louisiana, Mississippi, and Alabama.
By August 26 2005, the possibility of unprecedented cataclysm was already being considered.
Some computer models were putting the city of New Orleans right in the center of their track probabilities, and the chances of a direct hit were forecast at 17% (with strike probability rising to 29% by August 28).
This scenario was considered a potential catastrophe because 80% of the New Orleans metropolitan area is below sea level along Lake Pontchartrain.
Since the storm surge produced by the hurricane's right-front quadrant (containing the strongest winds) was more than 20 ft (6 m) near Biloxi, emergency management officials in New Orleans feared that the storm surge could go over the tops of levees protecting the city, causing major flooding.
This risk of devastation had been known for some time; previous studies by FEMA and the Army Corps of Engineers had warned that a direct hurricane strike on New Orleans could lead to massive flooding, which would lead to thousands of drowning deaths, as well as many more suffering from disease and dehydration, as the flood waters slowly receded from the city.
At a news conference 10:00 AM on August 28, shortly after Katrina was upgraded to a Category 5 storm, New Orleans mayor Ray Nagin ordered the first ever mandatory evacuation of the city, calling Katrina, "a storm that most of us have long feared".