NEW ORLEANS, Louisiana — As rain pounded at her windows Tuesday, Dorothy Ellis couldn't stop thinking about the two days she spent clinging to a tree after her New Orleans home was swallowed by floodwaters.

"It was bad, real bad," 60-year-old Ellis said, as she flipped through photographs of what Hurricane Katrina did, seven years ago, to the home that had been in her family for generations.

Now a new storm, Hurricane Isaac, was bearing down on the city, bringing with it devastating winds, storm surges and driving rain.

"That's where another house ran into my house," Ellis said as she showed a reporter snapshots of a younger self poking through the rubble for anything worth salvaging.

"I was staying with a friend. If I'd stayed in that house I'd have been dead."

Hurricane Isaac is not expected to be as fierce as Katrina, though flooding is expected as storm dumps as much as 20 inches (51 centimeters) of rain.

A huge surge of water pushed up from the Gulf of Mexico will likely spill over the tops of levees, even as the rain pours into storm drains and canals.

It's the timing that has many here on edge. Isaac's eye is set to strike on the anniversary of Katrina, a storm that killed nearly 1,800 people across the US Gulf Coast.

Hundreds drowned in their homes after levees long-warned to be inadequate burst under the pressure of Katrina's powerful storm surge and the bowl-like, low-lying city filled with floodwaters as deep as 15 feet (4.6 m).

More died in the chaos and violence that followed after officials bungled the response and left people stranded for days in the sweltering heat without food, water, medical help or any sense of security.

"We was hungry, we was dirty, we was tired," said Melody Barkum, 56, who spent two days stranded on her roof with nothing but the clothes on her back.

"After we lost everything, that's when I had my first heart attack, as soon as we got to Houston. Then I had two more. I'm surprised I'm still alive after the stress of it.

"It was awful worrying where you're going to stay, where your next meal is coming from and people acting so nasty like they didn't want us to be there instead of having sympathy.

"That's a terrible feeling when you have to beg for something to eat."

It was a neighbor with a boat who eventually plucked Ellis from the tree and took her to a nearby school, where she waited another four days before an official rescue crew dumped her unceremoniously at the Convention Center.

It was a hellish place, with no sanitation, no food, no water and corpses were piled up under blankets in plain sight.

Ellis waited with thousands of others for a bus ride to Houston and then had to flee again when Hurricane Rita bore down on Texas.

It was months before she could come home and New Orleans -- famed for its music, food and easy-going culture -- was a ghost town for years.

The Big Easy has made huge progress in rebuilding, but there are plenty of abandoned houses still bearing the marks of post-Katrina search and rescue crews.

"It ain't going to never be the same like it was before," Ellis told AFP.

It's all those missing people -- the ones who died, and thousands more who decided not to come home.

The fear and the flashbacks are hard to deal with, but not bad enough for Ellis and her friend Barkum to leave town.

They're living in a solid brick, three storey apartment for low-income seniors built after some of the rubble left behind in the hard-hit Lower Ninth Ward was cleared away.

"If we could survive Katrina, we can survive anything," Barkum said.