Hurricane Katrina was a large Category 5 Atlantic hurricane that caused over 1,800 deaths and $125 billion in damage in late August 2005, particularly in the city of New Orleans and the surrounding areas. It was at the time the costliest tropical cyclone on record and is now tied with 2017's Hurricane Harvey. The storm was the twelfth tropical cyclone, the fifth hurricane, and the third major hurricane of the 2005 Atlantic hurricane season, as well as the fourth-most intense Atlantic hurricane on record to make landfall in the contiguous United States.
Katrina originated on August 23, 2005, as a tropical depression from the merger of a tropical wave and the remnants of Tropical Depression Ten. Early the following day, the depression intensified into a tropical storm as it headed generally westward toward Florida, strengthening into a hurricane two hours before making landfall at Hallandale Beach on August 25. After briefly weakening to tropical storm strength over southern Florida, Katrina emerged into the Gulf of Mexico on August 26 and began to rapidly intensify.