Hurricane Katrina, tropical cyclone that struck the southeastern United States in late August 2005. The hurricane and its aftermath claimed more than 1,800 lives, and it ranked as the costliest natural disaster in U.S. history. The storm that would later become Hurricane Katrina surfaced on August 23, 2005, as a tropical depression over the Bahamas, approximately 350 miles (560 km) east of Miami. Over the next two days the weather system gathered strength, earning the designation Tropical Storm Katrina, and it made landfall between Miami and Fort Lauderdale, Florida, as a category 1 hurricane—a storm that, on the Saffir-Simpson scale,