Gustav howled into Cuba's Isla de Juventud as a monstrous Category 4 hurricane on Saturday while both Cubans and Americans scrambled to flee the path of the fast-growing storm.
Forecasters said it was just short of becoming a top-scale Category 5 hurricane as it powered its way toward the Gulf of Mexico on Sunday, before weakening a little ahead of a likely collision as early as Monday with the U.S. coast.
Gustav had already killed more than 80 people in the Caribbean, and if current forecasts hold up, it would make landfall early Tuesday morning along Louisiana's central coast, sparing New Orleans a direct hit.
But forecasters warned it was still too soon to say exactly where the storm will hit, and residents weren't taking any chances judging by the bumper-to-bumper traffic pouring from the city. Gas stations along interstate highways were running out of fuel, and phone circuits were jammed.
A mandatory evacuation order was expected as early as Saturday night. Hotels closed, and the New Orleans airport prepared to follow suit. Mayor Ray Nagin, saying the danger to the city was growing, told tourists to leave.
As part of the evacuation plan New Orleans developed after Hurricane Katrina, residents who had no other way to get out of the city waited on a line that snaked for more than a mile through the parking lot of the city's Union Passenger Terminal. From there, they were to board motor coaches bound for shelters in north Louisiana.
"I don't like it," said Joseph Jones Jr., 61, who draped a towel over his head to block the blazing sun. "Going someplace you don't know, people you don't know. And then when you come back, is your house going to be OK?"
Jones had been in line for 2 1/2 hours, but he wasn't complaining. During Katrina, he'd been stranded on a highway overpass.
Others led children or pushed strollers with one hand and pulled luggage with the other. Volunteers handed out bottled water, and medics were nearby in case people became sick from the heat.
Unlike Katrina, when thousands took refuge inside the Superdome, there will be no "last resort" shelter, and those who stay behind accept "all responsibility for themselves and their loved ones," said the city's emergency preparedness director, Jerry Sneed.
Yet the presence of 2,000 National Guard troops that were expected to join 1,400 New Orleans police officers patrolling the streets following the evacuation -- along with Gov. Bobby Jindal's request to neighboring states for rescue teams - suggested officials were expecting stragglers.
Many residents said the evacuation was more orderly than Katrina, although a plan to electronically log and track evacuees with a bar code system failed and was aborted to keep the buses moving. Officials said information on evacuees would be taken when they reached their destinations.
Advocates criticized the decision not to establish a shelter, warning that day laborers and the poorest residents will fall through the cracks.
Authorities in Mississippi, also battered by Katrina, had already begun evacuating the mentally ill and aged from facilities along the coast, and East Texas counties were making arrangements to do the same.
National Guard soldiers on Mississippi's coast were going door-to-door to alert thousands of families in FEMA trailers and cottages that they should be prepared to evacuate Sunday.
In Alabama, shelters were opened and 3,000 National Guard personnel assembled to help evacuees from Mississippi and Louisiana.