Gustav Huffs and Puffs and Hits Bayou

Hurricane Gustav may not have been the "mother of all storms" New Orleans Mayor Ray Nagin said he feared it could be, but the more than a million people who evacuated the Gulf Coast were warned this evening not to come back to the region too soon.

"I want to underscore the importance of not rushing back to your homes," Department of Homeland Security Secretary Michael Chertoff said. "You don't want to rush from shelter into a place of danger, whether it is weakness in a levee or power lines that are down or some other hidden vulnerability.

"Please give the authorities the time they need to check to make sure it is safe to come back," he said.

For many of the evacuees, the warning could be unnecessary. As Gustav churned northwards through Louisiana and into Texas, it was expected to bring massive flooding that could make many roads impassible.

Louisiana LeveePlay

Watch "Gustav Storms the Gulf" on a special edition of "20/20" at 10 p.m. ET

Nevertheless, in Baton Rouge there was a noticeable increase in cars out on the roads late today after the storm passed, and many of them were heading east toward New Orleans.

Officials blamed Gustav for at least seven deaths. Four people fleeing the storm were killed when their car struck a tree in Georgia, a couple died when a tree fell on the house where they were staying in Baton Rouge, and another woman died in a traffic accident in Louisiana.

New Orleans' levees, still not fully repaired after Hurricane Katrina three years ago, largely withstood the rising waters caused by the storm, though for a time officials in the southern Louisiana parish of Plaquemines feared a potential breech in a local levee there.

Superdome in New OrleansPlay

The levee overtopped and threatened to break late in the day. Parish President Billy Nungesser said the Braithwaite Levee could collapse, and urged any remaining residents to leave the area.

But emergency workers piled sandbags against the levee where the breach was feared, and later this evening officials said the danger had passed.

New Orleans was lashed with rain and winds that gusted up to 86 mph, and raised water levels so high along its rebuilt levees that water slopped over with each wave, but by the end of the day, the hurricane had been downgraded from a Category 2 to a Category 1 storm and the waters in New Orleans were receding.

Army Corps of Engineers spokesman Rene Poche said the levees were holding and that he did not expect any surge flooding.

The near miss for New Orleans drew a sigh of relief from city officials as well as the 200,000 city residents who fled.

Beverly Dobbs, who took in eight evacuees at her house in West Monroe, La., said her guests "were so relieved to see the newscast and find out that the storm didn't really hit, like Katrina."

Other New Orleans refugees in West Monroe planned to gather at a church that helped organize their evacuation.

"We're planning a celebration dinner -- we hope -- at the White's Ferry Road Church of Christ," Dobbs said.

Gustav, which was a monstrous Category 4 hurricane as it moved through the Caribbean early in the weekend, was later downgraded to a Category 2 hurricane and turned away from New Orleans in the hours before it made landfall.

Later in the day, the storm weakened even further and became a Category 1 hurricane, although it still clocked sustained winds of 90 mph.

It had plenty of punch, however, when it rumbled ashore about 10 a.m. at the bayou hamlet of Cocodrie, an area sparsely populated by shrimpers and oil rig workers. It packed winds of 110 mph and brought with it the threat of a storm surge as high as 14 feet. Gustav also brought the threat of tornadoes.

Gustav looked to be on a trajectory to create a swath of destruction northwest through Houma, Morgan City and on to Lafayette. The area is largely abandoned, thanks to the evacuation of 2 million people, the largest evacuation in U.S. history.

One woman was killed in a car wreck in Louisiana, and three other individuals with critical health conditions died when they were evacuated.

Louisiana Gov. Bobby Jindal said Gustav is expected to deflate to a tropical storm by tonight. Nevertheless, he said Gustav has left nearly 500,000 people in Louisiana without power.

Jindal said it was still too early to know when evacuees would be able to return home, but added it probably would not happen by Tuesday as initially announced by Nagin.

"It's certainly too, too early to say that it's safe for them to start coming back tomorrow," Jindal said at a press conference at the state's emergency operations center in Baton Rouge. "Tomorrow's too early; we need to let the storm come through.

The governor said 85 percent of south Louisiana gas stations were out of fuel, and the industry cannot move fuel until the winds slow down. He called on President Bush to release fuel from the strategic oil reserve, calling it "absolutely critical."

Entergy, the major utility in Louisiana, reports 500,000 of their 1.2 million customers in Louisiana have lost power, and the number continues to grow. Cleco Corp., which has 273,000 customers in the state, said the number of customers without power was at 50,000 and growing.

In Baton Rouge, 60 miles north of New Orleans, and the state's operating center for first responders, Mayor Kip Holden said two hospitals had lost power, but assured residents the situation was under control.

"This is not a doom and gloom scenario. For residents going through this for the first time, everything is going OK. We are seeing some things that are the same as Katrina, but we are getting through them," Holden said. "A lot of people are dependent on us right now. I assure them we are in control."

Mayor Tim Matte of Morgan City, about 80 miles west of New Orleans, told that a mandatory evacuation had succeeded in clearing out 75 percent of the population and the city was protected by a 24-foot seawall, with levees surrounding the city.

Matte predicted that the area of Houma, a major supply base for the oil industry, would be hardest hit.

Biggest Concern in Gustav's Path Is Levees

Houma Parish President Michel Claudet told that the lightly protected area was being hammered by 95 mph winds that were strong enough to peel back the roof of the parish firehouse and knockout power to their emergency services center.

Claudet said their biggest concern is that the area has no hurricane levees, and is protected only by drainage levees that are not prepared to handle storm surges from a Category 2 hurricane.

"All we have are drainage levees. We've got no hurricane protection. Drainage levees are not the same as storm protection levees," he said.

Gustav's earliest victim was the Republican presidential nominating convention in St. Paul, Minn. The GOP canceled its opening speeches, and Jindal's appearance at the convention was in doubt. Bush had already announced that he wasn't going and, instead, monitored Gustav from Austin, Texas. Jindal stayed at home to direct hurricane relief.

Republican presidential nominee Sen. John McCain, who was in New Orleans Sunday, went to a disaster relief center in Toledo, Ohio, today and helped pack boxes of cleaning supplies to be sent to areas hit by the hurricane.

"This is what it's all about..." McCain said after shaking hands with volunteers preparing the relief packages. "This epitomizes the millions of Americans who are serving on behalf of causes greater than their own self interest and putting their country first."

Bush said in the early hours of the storm that preparations and coordination between state and federal agencies had improved a great deal since Katrina three years ago.

"To that end, I feel good," Bush said. "The coordination on this storm is a lot better than during Katrina."

He warned, however, "This storm has yet to pass. It's a serious event,"

Gustav spared the Gulf's oil rigs, and the price of oil fell $4 in trading today as investors believed that the oil industry would suffer minimal losses. Gas prices could go up if the rigs, which were shut down for Gustav, can't resume pumping soon.

To the east of New Orleans, Mississippi's coastal towns, including Gulfport and Biloxi, were hit with power outages and flooded roadways.

New Orleans Levees Hold as Gustav Hits

To the west of New Orleans, Lafayette temporarily lost power and people were urged to fill their bathtubs with water as Gustav approached.

In New Orleans, about half the city lost power and winds and rain pummeled the nearly empty streets. In the Upper Ninth Ward, which was devastated by Katrina, only about six inches of flooding could be seen.

The big news in New Orleans was that its partially built levees, which were described as "fragile" in the days before Gustav struck, apparently stood up to the test.

Water splashed over the top of the Industrial Canal levee located in the city's Upper Ninth Ward. The flood wall there is 12.2 feet, and water levels peaked at around 11 feet.

Officials initially feared that two unmoored vessels in the canal could crash through the levee, but Maj. Gen. Don T. Riley of the U.S. Army Corps of Engineers said they were stable and posed no threat to the embankments.

"City pumps," he said, "will keep up with flooding in the interior."

He also said that Harvey Canal gate, one of the areas Nagin was particularly worried about failing, had stood up to the water and had not flooded.

Warned by Nagin that stragglers would be "on their own" if they stayed behind, nearly the entire population of New Orleans, including patients, the elderly and even pets, were hauled by bus, train and chartered planes to shelters farther north and out of reach of Gustav.

As the winds picked up, National Guard and police vehicles were pulled off the streets.

Nagin and other regional officials had warned residents to get out of town or it would be the "worst mistake of their lives," and this time, people heeded the warning. New Orleans' streets were empty with only a handful of hardy gamblers staying behind.

The few who stayed in New Orleans woke at dawn to slashing rain being driven through the city by winds of up to 67 mph and gusts up to 86 mph, making it difficult for a person to stand. Palm trees and street lights flailed in the wind. A billboard on Central Avenue was shredded.

In the French Quarter, the sound of windows popping was constant. Signs were smashed and dangling askew. A lamppost was toppled and a building's marquee collapsed.

Several hospitals were reportedly working off generators because they lost power. Despite the outages, the city's 23 massive drainage pumps continued to work.

At Tulane Medical Center, which took in 150 people for treatment on the night Hurricane Katrina struck in 2005, there were just 60 patients at the hospital. Officials said one baby was born last night.

Over 9,000 nursing home residents and hospital patients, some critically ill, were evacuated over the weekend, said Rear Adm. W. Craig Vanderwagen, assistant secretary for preparedness and response at the Department for Health and Human Services.

Gustav was the latest in what appears to be shaping up as a busy season of tropical storms. The storm was preceded by Fay, which never became strong enough to be classified as a hurricane, but killed 95 people in Haiti and the Dominican Republic before crisscrossing Florida a record four times and killing 11 more people with its drenching downpours.

Hanna Upgraded From Tropical Storm to Hurricane

On the horizon is Hanna. The tropical storm was upgraded to hurricane status today as it battered the Turks and Caicos chain of islands.

"Right now, the uncertainty is such that it could hit anywhere from Miami to the outer banks of North Carolina," said Jessica Schauer Clark, a meteorologist at the National Hurricane Center. "So, people really need to keep an eye on it."

The Associated Press and ABC News reporters Scott Mayerowitz, Eileen Murphy, Russell Goldman, Yunji de Nies, Marcus Baram and Dean Schabner contributed to this report