Isaac's whistling winds lashed New Orleans and the storm dumped nearly a foot of rain on its desolate streets, but the system of levee pumps, walls and gates appeared to withstand one of the stiffest challenges yet. To the north and south, though, people had to be evacuated or rescued as Isaac lingered over Louisiana.
The rain fell almost constantly for more than a day, flooding neighborhoods in a rural part of the state and in neighboring Mississippi. Officials had to respond quickly because the waters were rising fast even as Isaac meandered slowly northward Thursday on a path toward neighboring Arkansas.
President Obama declared federal emergencies in Louisiana and Mississippi late Wednesday, according to a statement from the White House. The disaster declarations free up federal aid for affected areas.
Along the shores of Lake Ponchartrain just north of New Orleans, officials sent scores of buses and dozens of high-water vehicles to help evacuate about 3,000 people as rising waters lapped against houses and left cars stranded. Floodwaters rose waist-high in some neighborhoods, and the Louisiana National Guard was working with sheriff's deputies to rescue people stranded in their homes.
The floodwaters "were shockingly fast-rising, from what I understand from talking to people," Lt. Gov. Jay Dardenne said. "It caught everybody by surprise."
Isaac arrived seven years after Hurricane Katrina and passed slightly to the west of New Orleans, where the city's fortified levee system easily handled the assault. But, low-lying area outside the city were harder hit.
"Hurricane Isaac has reinforced for us once again just how vulnerable these critical areas are," Democratic U.S. Sen. Mary Landrieu said.
New Orleans' biggest problems seemed to be downed power lines, scattered tree limbs and minor flooding. One person was reported killed, compared with 1,800 deaths from Katrina in Louisiana and Mississippi. And police reported few problems with looting. New Orleans Mayor Mitch Landrieu ordered a dusk-to-dawn curfew.
But in Plaquemines Parish, a sparsely populated area south of the city that is outside the federal levee system, dozens of people were stranded in flooded coastal areas and had to be rescued. The storm pushed water over an 18-mile levee and put so much pressure on it that authorities planned to intentionally puncture the floodwall to relieve the strain.
Officials rushed to evacuate more than 100 nursing home residents from Plaquemines Parish, an area with a reputation for weathering storms and perhaps the hardest hit by Isaac. In this hardscrabble, mostly rural parish, even the sick and elderly are hardened storm veterans.
"I don't think we had to evacuate to begin with," said Romaine Dahl, 59, as he sat in a wheelchair. "The weather was a hell of a lot worse last night than it is now. And I got an idea that after all this is said and done they're going to say everything is over with, go on back home."
By early Thursday, Isaac's maximum sustained winds had decreased to 45 mph and the National Hurricane Center said it was expected to become a tropical depression by Thursday night, meaning its top sustained winds would drop below 39 mph. The storm's center was on track to cross Arkansas on Friday and southern Missouri on Friday night, spreading rain as it goes.
Forecasters expected Isaac to move farther inland over the next several days, dumping rain on drought-stricken states across the nation's midsection before finally breaking up over the weekend.
Even at its strongest, the storm was far weaker than Hurricane Katrina, which crippled New Orleans in 2005. Because Isaac's coiled bands of rain and wind were moving at only 5 mph about the pace of a brisk walk the threat of storm surges and flooding was expected to linger Thursday as the immense comma-shaped system crawled across Louisiana.
The storm knocked out power to as many as 700,000 people, stripped branches off trees and flattened fields of sugar cane so completely that they looked as if a tank had driven over them.
In coastal Mississippi, officials used small motorboats Wednesday to rescue at least two dozen people from a neighborhood Isaac flooded in Pearlington. In addition, the National Weather Service said there were reports of at least three possible tornadoes touching down in coastal counties. No injuries were reported.
None of the reports had been confirmed. Until the weather clears, there is no way for survey teams to assess the area to determine whether damage was done by tornadoes or straight-line winds, said NWS Meteorologist Shawn O'Neil.
Back in New Orleans, the storm canceled remembrance ceremonies for those killed by Katrina. Since that catastrophe, the city's levee system has been bolstered by $14 billion in federal repairs and improvements. The bigger, stronger levees were tested for the first time by Hurricane Gustav in 2008.
As hard wind and heavy rain pelted Melba Leggett-Barnes' home in the Lower 9th Ward, an area leveled during Katrina, she felt more secure than she did seven years ago.
"I have a hurricane house this time," said Barnes, who has been living in her newly rebuilt home since 2008.
Her yellow house with a large porch and iron trellis was taking a beating but holding strong.
"I don't have power, but I'm all right," said Barnes, a cafeteria worker for the New Orleans school system.
This program aired on August 30, 2012. The audio for this program is not available.