NBC's Gabe Gutierrez reports on ongoing rescue efforts to reach dozens of people believed to be trapped in their homes due to flooding from an overtopped levee.
By Miguel Llanos, NBC News
Updated at 11 a.m. ET: New Orleans' levees and pumps were holding up to the rain and storm surge caused by Hurricane Isaac, but areas outside the defense network saw flooding, including an 18-mile stretch to the south where up to 12 feet of water invaded streets and homes.
Officials in Plaquemines Parish, where the surge overtopped an 8-foot levee, said National Guardsmen and even residents were rescuing people trapped in homes. Up to 60 people appear to be trapped, NBC's Gabe Gutierrez reported from the area. Rescuers earlier pulled several dozen to safety.
"We have flooding, inundated four-to-nine feet in areas on that side" of the levee, parish emergency management official Guy Laigast told the Weather Channel. "We've got homes that have been inundated. We have folks who are trapped in their residences."
"It's piling that water up on the east side of the Mississippi River," he added. "All that water is ponding up in that area and that's what's causing the overtopping."
The area had been under a mandatory evacuation order but only half of the 2,000 residents reportedly had left ahead of Isaac's landfall Tuesday.
The storm surge also flooded areas of the Mississippi coast with water rising several feet in some parts, authorities said. Weather Channel meteorologist Paul Goodloe reported a number of homes had been flooded in Biloxi Bay, Miss.
TODAY's Al Roker reports from New Orleans, La., where Hurricane Isaac has roared ashore with 80 mph winds.
"The entire stretch of U.S. 90 has been closed from the Bay St. Louis Bridge to the Biloxi Bay Bridge" due to flooding, he reported. The surge is close to overtopping the seawall between the beach and a grassy area off U.S. 90, he added. "And, by the way, high tide is coming up in a couple of hours."
Three adults and an infant stuck on a house boat in Hancock County, Miss., had to be rescued, NBC News reported, as low-lying areas were inundated with water.
At 7:35 a.m. ET, more than 450,000 homes and businesses were without power as a result of the storm, according to power company Entergy.
NBC's Lester Holt and Jim Cantore report from New Orleans, La., where the levees and systems of pumps are holding up against Hurricane Isaac. There was an overtopping towards the Gulf, but there has not yet been a breach.
"It's something I've never seen before," Plaquemines Parish President Billy Nungesser told the Weather Channel. "I rode out Katrina, and my home has more damage now. It has not let up one time throughout this whole event. The driving rain, all the telephone poles down in Plaquemines Parish. This is not a Category 1 storm."
The National Weather Service has issued flash flood warnings for the Orleans Parish, which includes New Orleans, Jefferson Parish, East Bank of Plaquemines Parish, Northwestern Plaquemines Parish, Western St. Bernard Parish and St. Charles Parish in Louisiana and Jackson County, Miss.
It also issued a string of tornado watch notices for the area affected by Isaac.
Rick Knabb, director of the National Hurricane Center, told The Weather Channel that the storm's large size meant it was "not going to fall apart real quick."
"So much of the circulation is over water, and so close to or over the warm waters of the Gulf of Mexico, there's really no reason why (Isaac) can't tap into the energy that warm water provides," he added.
"The large size means it's a bigger storm surge producer than a smaller Category 1," he noted. "It's slow motion means that the water is going to be piling up all day long and it's not going to go out today."
Hurricane Isaac brought more than just rain to Pass Christian, Miss., where the storm flooded out roads and scattered debris around the area. NBC's Janet Shamlian reports.
Combined with Isaac's slow movement, this meant there would be "elevated [seawater] surge levels all day today," he added.
In New Orleans, Mayor Mitch Landrieu said the post-Katrina investment in beefed up levees and pumps had paid off.
"It's holding up," he told NBC News. "There's no risk of any failure from what we can tell, anywhere."
Some 60 percent of the city was without power, however, he said.
"Of course, the longer the rain and the longer the wind, the greater the possibility of street flood in interior streets," he said earlier. "That wind is really, really heavy, which is why it is important that you stay inside."
"There are a lot of trees that are down," he added. "We have reports of streets being flooded in the city."
As Hurricane Isaac batters New Orleans, Plaquemines parish emergency director Guy Laigast speaks with NBC's Al Roker and Stephanie Abrams of The Weather Channel about flooding that has trapped some residents after water overtopped a levee.
Knabb also warned isolated areas would get up to 20 inches of rain with 7 to 14 inches falling over a widespread area. "We're going to see flooding out of this from the freshwater perspective" in addition to the seawater storm surge, he said.
The center of Isaac first made landfall Tuesday evening with 80 mph winds and then moved back over water before making a second landfall just west of Port Fourchon, La., around 2:15 a.m. local time (3:15 a.m. ET).
By late Wednesday morning, it had weakened slightly to 75 mph.
The Weather Channel's Jim Cantore and Stephanie Abrams, along with TODAY's Al Roker, reports from New Orleans, where Hurricane Isaac has made landfall.
Related: Follow Isaac's path with our storm tracker
Related: A resident reports from Mississippi town destroyed by Katrina
Related: Images, updates via Weather Channel
In Mississippi, Hancock County Emergency Management Director Brian Adam said early Wednesday that water stood up to 4 feet deep in the most vulnerable areas.
"Were still experiencing heavy winds, heavy rains" that should last overnight, he told NBC News. "We have road flooding in low-lying areas. ... We have about 7,200 without power.
"We’re kind of hunkered down to the point where we’re not doing a whole lot of traveling," he added.
Tornado warnings have been posted because of thunderstorms in southern Mississippi. But back streets of some communities showed little evidence of Isaac's passage save for occasional downed tree branches.
NBC's Michael Brunker as well as The Associated Press and Reuters contributed to this report.
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