MIAMI, Florida (CNN) -- Gustav's passage over Cuba took a toll on its wind speed, but it was heading over warmer Gulf waters, which are expected to reinvigorate the storm, according to the National Hurricane Center in Miami, Florida.
The storm's passage over Cuba shaved just 15 mph off the top wind speeds reported by the hurricane center before it made landfall on the island. Forecasters believe Gustav will quickly regain that power and more, likely growing to Category 4 status on Sunday.
Hurricane warnings were posted for the northern Gulf Coast from Cameron, Louisiana, eastward to the Alabama-Florida border, including the city of New Orleans, Louisiana and Lake Pontchartrain.
"It is important not to focus on the exact track of Gustav as this is a large hurricane and significant impacts are likely to occur well away from the center," according tothe hurricane center's 5 a.m. ET discussion.
A landfall around southern Louisiana is expected by Monday afternoon, theNational Hurricane Center said.
New Orleans Mayor Ray Nagin called Gustav "the mother of all storms," saying its destruction could outstrip that from Katrina, which flooded much of his city.
"You need to be scared," Nagin said. "You need to be concerned, and you need to get your butts moving out of New Orleans right now. This is the storm of the century."
The city's west bank is to evacuate at 8 a.m. Sunday.
Nagin said, so far, the city had evacuated roughly 10,000 people Saturday on buses, trains and planes, in addition to the thousands who left on their own. Buses from collection points would resume at 6 a.m. Sunday, he said.
"This storm is so powerful and growing more powerful every day," Nagin said. "I'm not sure we've seen anything like this."
At 5 a.m. ET, Gustav's eye was located 425 miles (680 kilometers) southeast of the mouth of the Mississippi River, with sustained winds near 125 mph. It was moving toward the northwest at 16 mph (26 kph).
"This storm could be as bad as it gets," Louisiana Gov. Bobby Jindal said Saturday afternoon. "We could see flooding even worse than we saw in Hurricane Katrina."
New Orleans joined the growing list of local governments in south Louisiana ordering mandatory evacuations on Saturday and Sunday as Gustav roared past Cuba and into the Gulf of Mexico.
Jindal did not order mandatory evacuations at a state level, but he urged residents to take the evacuations seriously.
"When it comes to evacuation, do it sooner rather than later, he said.
Jindal said the state planned to begin "contraflow" procedures, opening both sides of interstates to outgoing traffic only, at 4 a.m. Sunday.
In New Orleans, anxiety was high Saturday as residents fled, leaving behind a ghost town of boarded-up homes and empty streets.
Hundreds of people lined up for buses and trains to take them out of New Orleans and thousands of other Gulf Coast residents drove inland, clogging major highways.
At the Union Passenger Terminal in downtown New Orleans, people began arriving as early as 5:30 a.m., forming a line that snaked behind the main Amtrak terminal. Humvees circled the crowds of people, many who waited as long as 2½ hours, enduring the heat and relentless sun, unsure of their destination.
New Orleans officials designated 17 sites for people without transportation to board buses to take them to the terminal, where they will be moved to shelters outside New Orleans. However, scores of residents went directly to the terminal, prompting confusion, as did a glitch in the computer system being used to register people.
Jindal suspended registration at the terminal and instructed people to register when they arrive at shelters. By Saturday afternoon, 1,100 to 1,200 people had left the city on those buses, Nagin said.
"I'm not sure where I'm going," Margie Hawkins of New Orleans said. "My last 24 hours have been somewhat worrisome and very, very prayerful, because this is a very serious threat, and it's a lot of people to get to safe ground or be safe where they are."
The city also arranged with Amtrak for more than 7,000 seats to evacuate the elderly by train. About 1,500 people left for Memphis, Tennessee, Nagin said.
There were also crowds at New Orleans' Louis Armstrong International Airport, which the city plans to keep open through 6 p.m. CT Sunday. Both Delta Air Lines and AirTran Airways said they planned to continue flights in and out of New Orleans until the airport is closed.
Vehicles jammed Interstate 10 headed west toward Texas. Cars also clogged Interstates 55 and 59 heading north out of eastern Louisiana. Heavy volume was also reported on Interstates 65 and 59 as Mississippi evacuees streamed north.
Mississippi Gov. Haley Barbour announced Friday that Hurricane Katrina victims living in government-issued trailers or mobile homes along his state's coast would begin evacuating Saturday.
The storm called up uneasy memories of the deadly 2005 hurricane season, particularly of Katrina. When Katrina hit, more than 1,800 people died in five states, 1,577 of them in Louisiana.
Unlike the situation during Katrina, there will be no "shelter of last resort," the city said. In 2005, the city's Louisiana Superdome housed thousands of New Orleanians who couldn't, or didn't, heed the mandatory evacuation order.
Nagin warned that all but a "skeleton crew" of city workers would be leaving the city and said local authorities could not promise help for those who choose to stay behind.
"This is very, very serious, and we need you to heed this warning," he said. "We really don't have the resources to rescue you after this."