Hurricane Katrina was a large Category 5 Atlantic hurricane which caused over 1,800 deaths and $125 billion in damage in 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. The storm strengthened into a Category 5 hurricane over the warm waters of the Gulf of Mexico before weakening to Category 3 strength at its second landfall on August 29 over southeast Louisiana and Mississippi.
Flooding, caused largely as a result of fatal engineering flaws in the flood protection system known as levees around the city of New Orleans, precipitated most of the loss of lives. Eventually, 80% of the city, as well as large tracts of neighboring parishes, were inundated for weeks. The flooding also destroyed most of New Orleans' transportation and communication facilities, leaving tens of thousands of people who had not evacuated the city prior to landfall stranded with little access to food, shelter or basic necessities. The scale of the disaster in New Orleans provoked massive national and international response efforts; federal, local and private rescue operations evacuated displaced persons out of the city over the following weeks. Multiple investigations in the aftermath of the storm concluded that the U.S. Army Corps of Engineers, which had designed and built the region's levees decades earlier, was responsible for the failure of the flood-control systems, though federal courts later ruled that the Corps could not be held financially liable because of sovereign immunity in the Flood Control Act of 1928.The emergency response from federal, state and local governments was widely criticized, resulting in the resignations of Federal Emergency Management Agency (FEMA) director Michael D. Brown and New Orleans Police Department (NOPD) Superintendent Eddie Compass. Many other government officials were criticized for their responses, especially New Orleans Mayor Ray Nagin, Louisiana Governor Kathleen Blanco, and President George W. Bush, while several agencies, including the United States Coast Guard (USCG), National Hurricane Center (NHC), and National Weather Service (NWS), were commended for their actions. The NHC was especially applauded for providing accurate forecasts well in advance. Katrina was the earliest 11th named storm on record before being surpassed by Tropical Storm Kyle on August 14, 2020.