Isaac, a massive storm spanning nearly 200 miles from its center, made landfall at about 6:45 p.m. near the mouth of the Mississippi River. But it was zeroing in on New Orleans, about 90 miles to the northwest, turning streets famous for all-hours celebrations into ghost boulevards.
While many residents stayed put, evacuations were ordered in low-lying areas of Louisiana and Mississippi, where officials ordered the closure of the state's 12 shorefront casinos. By late Tuesday, more than 100,000 homes and businesses had lost power.
Ed Rappaport, deputy director of the National Hurricane Center, said Isaac's core would pass west of New Orleans with winds close to 80 mph and head for Baton Rouge.
"On this course, the hurricane will gradually weaken. Its winds will come down," Rappaport said Tuesday night from the Miami-based center. He said gusts could reach about 100 mph at times, especially at higher levels which could damage high-rise buildings in New Orleans.
As Isaac neared the city, there was little fear or panic. With New Orleans' airport closed, tourists retreated to hotels and most denizens of a coastline that has witnessed countless hurricanes decided to ride out the storm.
"Isaac is the son of Abraham," said Margaret Thomas, who was trapped for a week in her home in New Orleans' Broadmoor neighborhood by Katrina's floodwaters, yet chose to stay put this time. "It's a special name that means 'God will protect us'."
Still, the storm drew intense scrutiny because of its timing - just before the anniversary of Katrina and coinciding with the first major speeches of the Republican National Convention in Tampa, Fla., already delayed and tempered by the storm.
"We don't expect a Katrina-like event, but remember there are things about a Category 1 storm that can kill you," New Orleans Mayor Mitch Landrieu said, urging people to use common sense and to stay off any streets that may flood.
Other officials, chastened by memories and experience, advised caution. Tens of thousands of people were told to leave low-lying areas, including 700 patients of Louisiana nursing homes. At least one tornado spun off of Isaac in Alabama. There were no immediate reports of damage or injuries.
Many Gulf Coast residents opted to ride it out in shelters or at home and officials, while sounding alarm about the dangers of the powerful storm, decided not to call for mass evacuations like those that preceded Katrina, which packed 135 mph winds in 2005.
Isaac promises to test a New Orleans levee system bolstered after the catastrophic failures during Hurricane Katrina. But in a city that has already weathered Hurricane Gustav in 2008, calm prevailed.
"I feel safe," said Pamela Young, who settled in to her home in the Lower 9th Ward - a neighborhood devastated by Katrina - with dog Princess and her television. "Everybody's talking 'going, going,' but the thing is, when you go, there's no telling what will happen. The storm isn't going to just hit here."
Young, who lives in a new, two-story home built to replace the one destroyed by Katrina, said she wasn't worried about the levees.
"If the wind isn't too rough, I can stay right here," she said, tapping on her wooden living room coffee table. "If the water comes up, I can go upstairs."
While Isaac remained far less powerful than Katrina, it posed similar political challenges, a reminder of how the storm seven years ago became a symbol of government ignorance and ineptitude.
President Barack Obama sought to demonstrate his ability to guide the nation through a natural disaster and Republicans reassured residents they were prepared, all the while readying for the coronation of Mitt Romney. It was unclear Tuesday, what effect the storm might have on the festivities in Tampa, where Ann Romney and New Jersey Gov. Chris Christie are the night's featured speakers, after a day of delays.
There was already simmering political fallout from the storm. Republican Gov. Bobby Jindal, who canceled his trip to the convention in Tampa, said the Obama administration's disaster declaration fell short of the federal help he had requested. Jindal said he wanted a promise from the federal government to be reimbursed for storm preparation costs.
"We learned from past experiences, you can't just wait. You've got to push the federal bureaucracy," Jindal said.
FEMA Administrator Craig Fugate said such requests would be addressed after the storm.
Obama promised that Americans will help each other recover, "no matter what this storm brings."
"When disaster strikes, we're not Democrats or Republicans first, we are Americans first," Obama said at a campaign rally at Iowa State University. "We're one family. We help our neighbors in need."
While politicians from both parties were careful to show their concern for those in the storm's path, Gulf residents and visitors tried to make the best of the situation on the ground.
In New Orleans' French Quarter, Hyatt hotel employee Nazareth Joseph braced for a busy week and fat overtime paychecks. Joseph said he was trapped in the city for several days after Katrina and helped neighbors escape the floodwaters.
"We made it through Katrina; we can definitely make it through this. It's going to take a lot more to run me. I know how to survive," he said.
Tourists seemed to be taking Isaac in stride.
Maureen McDonald of Long Beach, Ind., strolled the French Quarter on her 80th birthday wearing a poncho and accompanied by family who traveled from three different cities to meet her in New Orleans to celebrate.
"The storm hasn't slowed us down. We're having the best time."
Maureen's son, Bob McDonald, said the group considered canceling the trip, but the thought passed quickly.
"We just figured why not get the full New Orleans experience, hurricane and all," Bob McDonald said. As they walked through the French Quarter Tuesday morning, they took pictures of media trucks parked near Bourbon Street and businesses boarding up windows.
But farther east along the Gulf, veterans of past hurricanes, made sure to take precautions.
At a highway rest stop along Alabama's I-10, Bonnie Schertler, 54, of Waveland, Miss., summed up why she left her home on the coast for her father's home in Red Level, Ala., after hearing forecasts that the storm could get stronger and stall.
"I left because of the 'coulds,'" said Schertler, whose former home in Waveland was destroyed in Hurricane Katrina. "I just feel like the storm may stay for a few days and that wind might just pound and pound and pound and pound," she said.
"A slow storm can cause a lot more havoc, a lot more long-term power outage, 'cause it can knock down just virtually everything if it just hovers forever," she said.
Those concerns were reinforced by local officials, who imposed curfews in Mississippi's Harrison, Hancock and Jackson counties. The Mississippi Gaming Commission on Tuesday ordered the closing of all coast casinos, which are on or near the water.
"This storm is big and it's tightening up and it sat out there for 12 hours south of us and it's pushing that wave action in and there's nowhere for that water to go until it dissipates," said Harrison County Emergency Operations Director Rupert Lacy.
All along U.S. 90, families stood at the edge of the waves to gawk. The Mississippi Sound, protected by barrier islands, is often as still as a lake, but Isaac began stirring breakers before dawn, as it pumped a storm tide toward the coast. Police struggled to clear public piers where water was lapping at the boards, and resorted to bullhorns to try to get sightseers to leave the beach. But people were still coming down to the edge to take a look around 2 p.m., as it began to rain heavily in Gulfport.
Closer to the beachfront in Pass Christian, Steve Ladner was waiting for customers at Martin's Hardware. The 80-year-old hardware store only had one wall standing after Katrina, but was rebuilt as part of a small shopping center in the western Harrison County town, where well-off New Orleanians have long maintained grand beach homes.
Ladner said business was strong from 8 a.m. to about noon, as he sold rope, lights, batteries and other hurricane supplies. "All hurricane sales final" said the sign on the counter. Business dried up quickly at midday. "It's over now," Ladner said.
Customers said they were staying, Ladner said, even though all of Pass Christian was included in a mandatory evacuation order that began at noon.
"It's good for business, but you don't want to make your money like this," Ladner said.
And in Theodore, Ala., 148 people had taken refuge in an emergency shelter set up at the town's high school by midday Tuesday, with minds focused as much on the past and the present storm.
Charlotte McCrary, 41, spent the night along with her husband Bryan and their two sons, 3-year-old Tristan and 1-year-old Gabriel. She spent a year living in a FEMA trailer after Hurricane Katrina, which destroyed her home, and said she still hasn't gotten back to the same place where she was seven years ago.
"I think what it is," Bryan McCrary said, "is it brings back a lot of bad memories."
This story was reported by Associated Press writers Cain Burdeau in New Orleans, Kevin McGill in Houma, La., Holbrook Mohr in Waveland and Pass Christian, Miss., Jeff Amy in Biloxi and Gulfport, Miss., Jay Reeves in Gulf Shores, Ala., Jessica Gresko in Coden, Ala., Julie Pace in Ames, Iowa and Curt Anderson at the National Hurricane Center in Miami.