Hurricane Katrina was a devastating and deadly tropical cyclone that caused 1,392 fatalities and damages estimated at $186.3 billion (2022 USD) in late August 2005, particularly in the city of New Orleans and its surrounding area. Katrina was the twelfth tropical cyclone, the fifth hurricane, and the third major hurricane of the 2005 Atlantic hurricane season. It was also the fourth-most intense Atlantic hurricane to make landfall in the contiguous United States, gauged by barometric pressure.

Katrina formed on August 23, 2005, with the merger of a tropical wave and the remnants of Tropical Depression Ten. Early the following day, the depression intensified into a tropical storm and headed generally westward toward Florida. On August 25, two hours before making landfall at Hallandale Beach, it strengthened into a hurricane. After briefly weakening to tropical storm strength over southern Florida, Katrina entered the Gulf of Mexico on August 26 and rapidly intensified. The storm strengthened into a Category 5 hurricane over the warm waters of the Gulf of Mexico before weakening to a high-end Category 3 hurricane at its second landfall on August 29 over southeast Louisiana and Mississippi.

The largest loss of life in Hurricane Katrina was due to flooding caused by engineering flaws in the flood protection system, particularly the levees around the city of New Orleans. Eventually, 80% of the city, as well as large areas in neighboring parishes, were flooded for weeks.