Hurricane Katrina, the tropical cyclone that struck the Gulf Coast in August 2005, was the third-strongest hurricane to hit the United States in its history at the time. With maximum sustained winds of 175 mph, the storm killed a total of 1,833 people and left millions homeless in New Orleans and along the Gulf Coast of Louisiana, Mississippi and Alabama.

The heavy death toll of the hurricane and the subsequent flooding it caused drew international attention, along with widespread and lasting criticism of how local, state and federal authorities handled the storm and its aftermath.

The storm initially formed as a tropical depression southeast of the Bahamas on August 23. By the evening of August 25, when it made landfall north of the Broward-Miami-Dade county line, it had intensified into a category 1 hurricane. With top winds of around 80 mph, the storm was relatively weak, but enough to knock out power for about 1 million and cause $630 million of damage.

After passing over Florida, Katrina again weakened, and was reclassified as a tropical storm. But over the Gulf of Mexico, some 165 miles west of Key West, the storm gathered strength above the warmer waters of the gulf. On August 28, the storm was upgraded to a category 5 hurricane, with steady winds of 160 mph.

On the morning of August 29, 2005, Katrina made landfall around 60 miles southeast of New Orleans. Within an hour, nearly every building in lower Plaquemines Parish would be destroyed. Though downgraded to a category 3, the storm’s relatively slow forward movement (around 12 mph) covered the region with far more rain than a fast-moving storm would have. Winds of 125 mph and storm surges of 28 feet devastated much of Biloxi and Gulfport, Mississippi.

At 5 a.m. on August 29, the U.S. Army Corps of Engineers, which administered the levees, received a report that water had broken through the concrete flood wall between the 17th Street Canal and the city. The Industrial Canal was later breached as well, flooding the neighborhood known as the Lower Ninth Ward.

By late afternoon, the breaching of the London Avenue Canal levees had left 80 percent of New Orleans underwater. In some areas, floodwaters reached depths of 10 to 15 feet, and didn’t recede for weeks. Although New Orleans’ levees and flood walls had been designed to withstand a category 3 hurricane, half of the network gave way to the waters.

By some estimates, between 80 and 90 percent of New Orleans’ population was able to evacuate the city prior to Katrina. Still, about 100,000 people were trapped in the city when the storm hit, and many took last-ditch refuge in the New Orleans Superdome and the Ernest J. Morial Convention Center as the storm approached. Some 25,000 crowded into the convention center, while more than 25,000 filled the Superdome.

As Katrina moved inland over Mississippi, it weakened to a Category 1 hurricane and later to a tropical storm. By 11 a.m. on August 30, Katrina had dwindled to heavy rainfall and winds of about 35 mph. Meanwhile, flooding continued to worsen in New Orleans.

The arrival of 13,000 U.S. National Guard troops and 7,000 U.S. military troops deployed by President George W. Bush helped with evacuations and resupplying food and water to those stranded at the Superdome and convention center, all of whom were finally evacuated on September 3. Many Katrina evacuees made it to Houston, Texas, where they were housed in the Astrodome and other shelters.

Katrina’s death toll is the fourth highest of any hurricane in U.S. history, after the Galveston Hurricane of 1900, which killed between 8,000 and 12,000 people; Hurricane Maria, which killed more than 4,600 people in Puerto Rico in 2017; and the Okeechobee Hurricane, which hit Florida in 1928 and killed as many as 3,000.

In Louisiana, where more than 1,500 people are believed to have died due to Katrina’s impact, drowning (40 percent), injury and trauma (25 percent), and heart conditions (11 percent) were the major causes of death, according to a report published in 2008 by the American Medical Association.

The Data Center, a New Orleans-based research organization, estimated that the storm and subsequent flooding displaced more than 1 million people, leaving hundreds of thousands of people homeless. It damaged more than a million housing units in the region. According to the National Oceanic and Atmospheric Administration (NOAA), Katrina is the costliest U.S. hurricane on record, inflicting some $170 billion in total damages.

Widespread criticism of the federal response to Katrina led to the resignation of Michael D. Brown, director of the Federal Emergency Management Agency (FEMA), and did lasting damage to the reputation of President Bush, who was nearing the end of a month-long vacation at his ranch in Crawford, Texas when Katrina struck.

In 2006, the U.S. Army Corps of Engineers, which was responsible for the design of the levee system in New Orleans, acknowledged that outdated and faulty engineering practices used to build the levees led to most of the flooding that occurred due to Katrina. On the state and local level, Louisiana Gov. Kathleen Blanco and New Orleans Mayor Ray Nagin were criticized for not ordering mandatory evacuations sooner. Blanco declined to seek reelection in 2007, and died in 2019. Nagin left office in 2010, and was later convicted on charges of bribery, fraud and money laundering committed while in office.

The mass exodus from the Gulf Coast and New Orleans during and after Katrina represented one of the largest and most sudden relocations of people in U.S. history. Some 1.2 million Louisianans were displaced for months or even years, and thousands never returned.

In April 2000, according to the Data Center, the population of New Orleans was 484,674; by July 2006, not quite a year after Katrina, it had dropped by more than 250,000, to some 230,172. Some of those who left later returned, and by 2020 the population reached just over 390,000, or about 80 percent of its pre-Katrina population.