As New Orleans battened down its hatches Sunday, evacuations were ordered, the Superdome was turned into a shelter, and emergency plans swung into effect against a flood threat the below-sea-level city has long dreaded.
The danger is also real in Alabama and Mississippi, where many in coastal areas rushed Sunday to get out of harm's way and onto higher ground.
The storm might spare New Orleans a direct hit, while posing a greater danger to the coastal Mississippi cities of Gulfport and Biloxi.
Three residents of a Louisiana nursing home died late Sunday while trying to get out of the path of the storm, according to CBS News Affiliate WWL-TV, which reports the three people were killed in an incident involving a school bus in the Baton Rouge area.
Click here for live Webcast coverage of Hurricane Katrina, from CBS News Affiliate WWL-TV in New Orleans.
Because of its size, with hurricane-force winds extend up to 105 miles from the center, and its potential to spawn tornadoes - even areas far from the landfall could be devastated.
"It's capable of causing catastrophic damage," said Max Mayfield, director of the National Hurricane Center, referring to the danger for New Orleans. "Even well-built structures will have tremendous damage. Of course, what we're really worried about is the loss of lives... New Orleans may never be the same."
Much of coastal Alabama was evacuated Sunday as emergency officials warned that Hurricane Katrina could bring historic flood levels to Mobile's downtown riverfront and leave bayou and beachfront roads under a sea of water. Mobile Mayor Michael Dow said the possible flooding could be worse than the 9-foot surge that soaked downtown and turned a key interstate connector into a lake during Hurricane Georges in 1998.
Evacuations were also ordered in coastal Mississippi, as the many floating casinos in the area packed up their chips and closed.
Hundreds of thousands in the three states heeded official advice Sunday to evacuate, some heading to shelters and others clogging the roads as they tried to reach friends, relatives and motels on higher ground.
"Have God on your side, definitely have God on your side," Nancy Noble said as she sat with her puppy and three friends in six lanes of one-way traffic on gridlocked Interstate 10 in Louisiana. "It's very frightening."
"I'm really scared," said Linda Young as she filled her gas tank near New Orleans. "I've been through hurricanes, but this one scares me. I think everybody needs to get out."
Because much of New Orleans is below sea level in a basin, a complex levee system is New Orleans' only protection from major flooding. Chief Joseph Matthews of the Office of Emergency Preparedness tells CBS News that if the levees wind up underwater, the resulting floods could take as long as two weeks to drain.
Dr. Walter Monsour, director of emergency management in the New Orleans area, says the city is "going to experience a significant tidal surge" and is asking evacuees to stay out of town until well after the storm - to give authorities time to assess the expected damage.
Rain began falling on southeastern Louisiana at midday Sunday, the first hints of a storm with a potential surge of 18 to 28 feet, topped with even higher waves, tornadoes and as much as 15 inches of rain.
"We are facing a storm that most of us have long feared," Mayor Ray Nagin said in ordering the mandatory evacuation for his city of 485,000 people, surrounded by suburbs of a million more. "The storm surge will most likely topple our levee system."
"This is very serious, of the highest nature," said Nagin. "This is a once-in-a-lifetime event."
President Bush, as he readied the federal government for a massive relief effort, on Sundayto forget anything but their safety and move to higher ground as instructed.
New Orleans hasn't been this concerned about a storm since Hurricane Betsy blasted the Gulf Coast in 1965. Flooding approached 20 feet deep in some areas, fishing villages were flattened, and the storm surge left almost half of New Orleans under water and 60,000 residents homeless. Seventy-four people died in Louisiana, Mississippi and Florida.
For years, forecasters have warned of the
Estimates have been made of flooding that could overrun levees with the potential to turn many neighborhoods in New Orleans into a 30-foot-deep toxic lake filled with chemicals and petroleum from refineries, and waste from ruined septic systems.
Despite the dire predictions, a group of residents in a poor neighborhood of central New Orleans sat on a porch with no car, no way out and, surprisingly, no fear.
"We're not evacuating," said 57-year-old Julie Paul. "None of us have any place to go. We're counting on the Superdome. That's our lifesaver."
The Superdome, the 70,000-seat home of football's Saints and the New Year's Sugar Bowl, opened at daybreak Sunday, giving first priority to frail, elderly people on walkers, some with oxygen tanks. They were told to bring enough food, water and medicine to last up to five days.
In the French Quarter, most bars that stayed open through the threat of past hurricanes were boarded up and the few people on the streets were battening down their businesses and getting out.
Sasha Gayer tried to get a train out of town but couldn't. So she walked back to the French Quarter, buying supplies on the way, and then stopped at one of the few bars open on Bourbon Street.
"This is a lot more fun than sitting at home listening to apocalyptic media reports," she said. "This is how you know it's a serious hurricane. You can't find a slice of white bread in the city, but you can still buy beer."
Katrina is "unmitigated bad news" for motorists across the nation because it shut down offshore production of at least 1 million barrels of oil daily and threatened refinery and import operations around New Orleans.