Why Hurricane Katrina was so uniquely catastrophic — and remains America’s most devastating storm, 20 years later

On Aug. 29, 2005 — exactly 20 years ago today — Hurricane Katrina made landfall in Louisiana. America hasn’t suffered a storm as devastating since.

Katrina’s winds, rains, floodwaters and aftereffects killed nearly 1,400 people across the South; more than 600 went missing. Only the Galveston, Texas, hurricane of 1900 and the Lake Okeechobee, Fla., hurricane of 1928 are known to have claimed more lives.

Total damages from Katrina surpassed $125 billion, making it the costliest natural disaster in U.S. history. Entire coastal communities were obliterated, and some of the lowest-lying — and poorest — New Orleans neighborhoods were wiped out by a storm surge that reached as high as 28 feet.

A botched government response — on the federal, state and local level — only made matters worse.

Two decades later, here’s a look back at why Hurricane Katrina was so uniquely catastrophic.

The tropical depression that ultimately became Katrina formed over the southeastern Bahamas on Aug. 23, 2005. By the following morning, it had become a tropical storm. The next day, it crossed over South Florida as a Category 1 hurricane.

The real trouble started, however, when Katrina reached the unusually warm waters of the Gulf of Mexico, where it started to rapidly intensify. By Aug. 27, Katrina was a Category 3 storm; that same day, a meteorological phenomenon known as an eyewall replacement cycle caused it to nearly double in size. Within just nine hours, Katrina had strengthened from a Category 3 to Category 5, with maximum sustained winds of 175 miles per hour.

At the time, it was the strongest hurricane ever recorded in the Gulf.

When Katrina made landfall in Louisiana on Aug. 29, it had weakened slightly to a Category 3. But it was still generating sustained gusts of 120 miles per hour, with hurricane-force winds extending outward for 120 miles. Underscoring its raw power, Katrina wasn’t downgraded to a tropical storm until it had traveled 150 miles inland.

Initially, forecasters expected Katrina to turn north and hit the Florida Panhandle. But it looped toward New Orleans instead. As it churned across the Gulf, the storm pushed a wall of water ahead of it. On Aug. 28, New Orleans Mayor Ray Nagin ordered the first-ever mandatory evacuation of the city, calling Katrina the “storm that most of us have long feared.” An estimated 1.3 million people complied, but many refused. The same day, the National Weather Service’s New Orleans/Baton Rouge office predicted that the area would be “uninhabitable for weeks” after “devastating damage.”

Much of the city of New Orleans and the surrounding metro area sits below sea level. Existing federally built levees offered 23 feet of protection — but they were no match for Katrina’s storm surge. When it struck on Aug. 29, the water breached various flood protection structures in 53 places, submerging 80% of the city. Poor design and construction were partly to blame: short, inadequate sheet pilings and weak foundation materials like sand and clay.

Lower-income, predominantly Black neighborhoods such as the Lower Ninth Ward were hardest hit; homes were swept off their foundations. Hurricane-force winds blew out windows and ripped part of the roof off the Superdome, where approximately 26,000 people were sheltering. Eight to 15 inches of rain fell across Louisiana in a matter of hours. The coasts of Mississippi and Alabama were decimated as well.

In the aftermath of Katrina, national attention turned toward the government’s disaster response — and the officials who had been in charge of leading it.

In Louisiana alone, 900,000 people had lost power; major roads into and out of New Orleans were impassable; communications were cut off. With corpses still floating in the streets, some survivors struggled to find food and fresh water. Nagin was criticized for delaying his evacuation order until less than a day before landfall and failing to implement a flood plan. The Federal Emergency Management Agency was slammed for its slow, insufficient response; FEMA head Michael Brown was soon forced to resign. President George W. Bush came under fire as well, and his political standing never recovered.

The controversy came to be known as Katrinagate.

In the end, more than 200,000 New Orleans homes were damaged or destroyed, and more than 800,000 residents were displaced — the greatest displacement in the U.S. since the Dust Bowl of the 1930s. Reconstruction and repopulation efforts took years. Even now, two decades later, the city of New Orleans still bears the scars of Hurricane Katrina.