(CNN) -- The fury of Isaac slammed into southeast Louisiana with strong winds and pounding rain, generating the first real test early Wednesday of flood control systems and emergency services in New Orleans on the seventh anniversary of Hurricane Katrina.
With forecasters warning Isaac was generating dangerous storm surges and flooding from heavy rain, all eyes were on the New Orleans levee system that was rebuilt and reinforced at a cost of $14 billion after it failed when Katrina struck in 2005.
Nearly 1,800 people died in Katrina, the majority when levees failed and flooded New Orleans.
"People who went through Katrina are pretty nervous about storms, and large numbers of people have left," Lynn Magnuson, 58, said in a CNN iReport.
Magnuson said the Lower 9th Ward, which was hard hit by Katrina, "is pretty empty right now."
Issac made its second landfall at about 2 a.m. CT (3 a.m. ET) near Port Fourchon, 60 miles southeast of New Orleans, in southeast Louisiana after slamming first into Plaquemines Parish along the coast and then wobbling back over the water near the mouth of the Mississippi River, the National Hurricane Center said in an early morning updated.
After stalling along the coast, the hurricane was moving at about 8 mph -- with sustained winds of 80 mph, the hurricane center said.
The worst of the storm was expected to hit New Orleans later in the morning Wednesday, though the first to feel its fury was Plaquemines Parish where Isaac first made landfall Tuesday night before moving back out over the water toward the mouth of the Mississippi River.
Emergency management officials reported the overtopping of an 18-mile stretch of a back levee in Plaquemines Parish from Braithwaite to White Ditch, which will "result in significant deep flooding in the area," the National Weather Service of New Orleans said in a statement early Wednesday.
That levee was not upgraded as part of the flood defense upgrades that occurred following Katrina, parish president Billy Nungesser told CNN. The levee, according to the National Weather Service, is maintained by the parish and not part of the federal hurricane protection levee system.
Officials were trying to get to two pump operators stuck on a levee as flood waters rose. A resident is going to take his own boat to attempt to rescue them, Nungesser said.
"Last we talked they were safe," he said.
The area was under a mandatory evacuation, though Nungesser said he knows of between six and eight people who stayed behind to ride out the storm.
There are reports of up to 12 feet of water in some areas. "If they have a second floor, they need to get it," Nungesser said.
Current weather conditions were making it difficult for anyone to check on those who stayed behind.
"We took the brunt of Katrina, and we are doing it again for this one," Nungesser said.
Strong winds ripped through the parish, knocking down utility and power poles.
At Nungesser's brick house, he said the wind was so strong that "it's pushing rain through the cracks" into the house.
"The light sockets are spraying you with water like you a hose hooked up there," he said.
Even with more dangerous conditions likely yet to come, the storm already has caused significant surges and flooding in a number of locales, and not just those directly in Isaac's path. Storm surges of 9.9 feet have been reported in Shell Beach, Louisiana, and 6.2 feet in Waveland, Mississippi, according to the hurricane center.
These surges likely will get worse, with forecasters predicting water levels to rise between 6 to 12 feet on the coast in Mississippi and southeastern Louisiana alone.
The National Weather Service, meanwhile, warned early Wednesday that heavy rainfall across metropolitan New Orleans and nearby coastal communities will likely result in flash floods.
In Biloxi, Mississippi, 50-year-old Alfonso Walker was keeping a close on the progress of the 195-mile wide hurricane.
He watched as a storm surge sent waves crashing over the pier at the IP Biloxi Hotel & Casino.
"I went through Hurricane Camille in 1969 and Hurricane Katrina in 2005, where I lost everything, and every other hurricane in between those two that came through," he said in a CNN iReport.
"So I'm a little concerned."
Isaac, which started as a tropical storm last week in the Atlantic Ocean, killed nearly two dozen people in Haiti and the Dominican Republic before starting its journey across the Gulf of Mexico.
On Tuesday, Isaac was classified as a Category 1 hurricane. It is significantly weaker than Category 3 Katrina, though forecasters warn it is capable of causing significant flooding.
"There is no evidence of any (water) overtopping (canals)," New Orleans Mayor Mitch Landrieu said. "We have full confidence the levees will hold."
Even so, he and other officials were taking no chances.
"We're in a hunker down phase now, because this storm could be over us for a while with a lot of wind and rain," Landrieu said.
"Hunker down means hunker down and prepare to ride it out."
The mayor tweeted that about 1,000 National Guard troops and more than 2,900 law enforcement officers are in the city ready to address issues related to the storm.
Power had been knocked out to more than 310,000 customers in Louisiana by the storm, while localized street flooding and downed electrical wires were reported across the city, according to officials. A handful of residents also were evacuated after trees uprooted by wind smashed into several homes, the city said.
Isaac earlier prompted three airports to close -- in New Orleans; Gulfport-Biloxi, Mississippi; and Mobile, Alabama -- and cancellations of around 1,500 flights, according to airline and airport officials.
Major ports along the Gulf Coast and the Mississippi River from Baton Rouge to its mouth have been closed, according to the Coast Guard.
Amtrak suspended its train service to and from New Orleans on Wednesday because of Isaac.
Business also came to a standstill because of Isaac.
Fifty-two Walmart and Sam's Club stores in Louisiana and nine in Mississippi were shuttered Tuesday, their parent company said.
In Mississippi, more than 1,800 people were staying in 33 shelters located in 16 counties, according to the state's emergency management agency.
Shrimpers in Bayou Le Batre, Alabama, were among those who heeded official warnings and hunkered down.
The Nuclear Regulatory Commission said it was sending additional inspectors to two Louisiana nuclear plants in the storm's path, as power company Entergy planned a "controlled shutdown" of one of them starting Tuesday afternoon.
Wholesale gas prices declined Tuesday after surging nearly 8 cents a day earlier as then-tropical storm Isaac veered toward the Gulf Coast, causing many oil refineries to shut down as a precaution.
Analysts said panic buying was over and that Isaac was unlikely to do lasting damage to oil refineries and infrastructure along the Gulf Coast.
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