''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. ''It's very frightening.''
Three nursing home patients died during the evacuation, authorities said.
Katrina intensified into a Category 5 giant over the warm water of the Gulf of Mexico, reaching top winds of 175 mph before weakening slightly on a path to hit New Orleans after sunrise today. It would be New Orleans' first direct hit in 40 years and the most powerful storm ever to slam the city.
Hurricane force winds were expected to reach Grand Isle, 60 miles south of New Orleans, by 1 a.m., and the eye of the hurricane was forecast to hit the barrier island around 8 a.m.
Forecasters warned that Mississippi and Alabama were also in danger because Katrina was such a big storm. Its hurricane-force winds extended up to 105 miles from the center and the storm packed the potential for a surge of 18 to 28 feet, 30-foot waves and as much as 15 inches of rain.
''The conditions have to be absolutely perfect to have a hurricane become this strong,'' National Hurricane Center Director Max Mayfield, noting that Katrina may yet be more powerful than the last Category 5 storm, 1992's Hurricane Andrew, which at 165 mph leveled parts of South Florida, killed 43 people and caused $31 billion in damage.
''It's capable of causing catastrophic damage,'' Mayfield said. ''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.''
By evening, the first squalls, driving rains and lightning began hitting New Orleans. A grim Mayor C. Ray Nagin earlier ordered the mandatory evacuation for his city of 485,000, conceding Katrina's storm surge pushing up the Mississippi River would swamp the city's system of levees, flooding the bowl-shaped city and causing potentially months of misery.
''We are facing a storm that most of us have long feared,'' he said. ''This is a once-in-a-lifetime event.''
As many as 100,000 inner-city residents didn't have the means to leave and an untold number of tourists were stranded by the closing of the airport, so the city arranged buses to take people to 10 last-resort shelters, including the Superdome.
For years, forecasters have warned of the nightmare flooding a big storm could bring to New Orleans, a bowl-shaped city bounded by the half-mile-wide Mississippi River and massive Lake Pontchartrain.
As much as 10 feet below sea level in spots, the city is as the mercy of a network of levees, canals and pumps to keep dry.
Scientists predicted Katrina could easily overtake that levee system, swamping the city under a 30-feet cesspool of toxic chemicals, human waste and even coffins that could leave more than 1 million people homeless.
''All indications are that this is absolutely worst-case scenario,'' Ivor van Heerden, deputy director of the Louisiana State University Hurricane Center, said Sunday afternoon.
Jefferson Parish President Aaron Broussard said some who have ridden out previous storms in the New Orleans area may not be so lucky this time.
''I'm expecting that some people who are die-hards will die hard,'' he said.
For those who were evacuated, it wasn't an easy trip. Traffic was backed up bumper-to-bumper on many highways.
Three nursing home patients being bused to a Baton Rouge church died, one aboard the bus, another at the church and the third at a hospital, the local coroner said Sunday. ''These folks are pretty fragile when they're put on these buses,'' said Don Moreau, of the East Baton Rouge Parish Coroner's Office.
Katrina was a Category 1 storm with 80-mph wind when it hit South Florida with a soggy punch Thursday that flooded neighborhoods and left nine people dead. It strengthened rapidly in the Gulf of Mexico as it headed for New Orleans.
Despite the dire warnings, 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 Julie Paul, 57. ''None of us have any place to go. We're counting on the Superdome. That's our lifesaver.''
The 70,000-seat Superdome, the home of football's Saints, 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.
''They told us not to stay in our houses because it wasn't safe,'' said Victoria Young, 76, who sat amid plastic bags and a metal walker. ''It's not safe anywhere when you're in the shape we're in.''
Fitter residents waited for hours in the muggy heat and then pouring rain to get in, clutching meager belongings and crying children. By nightfall, at least 8,000 refugees were safely inside, seated in the stands because of fears the field could flood.
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. But a few stragglers remained.
Tony Peterson leaned over a balcony above Bourbon Street, festooned with gold, purple and green wreathes as Katrina's first rains pelted his shaved head.
''I was going to the Superdome and then I saw the two-mile line,'' the 42-year-old musician said. ''I figure if I'm going to die, I'm going to die with cold beer and my best buds.''
