Hurricane Katrina, Tropical cyclone that struck the U.S. in 2005. The storm that became Hurricane Katrina was one of the most powerful Atlantic storms on record, with winds in excess of 170 mi (about 275 km) per hour. On August 29, 2005, the hurricane struck the Gulf Coast and caused massive destruction in Louisiana and Mississippi. The levee system in New Orleans failed, and, by August 30, about 80 percent of the city was underwater. A public-health emergency ensued, and some neighborhoods experienced substantial amounts of looting and civil disorder. A military presence was established in the city on September 2. Ultimately, the storm and its aftermath claimed nearly 1,400 lives and caused more than $125 billion (about $200 billion in 2024 dollars) in damage. It is the costliest natural disaster in U.S. history.