(NEW ORLEANS) -- More than 700,000 people have been left without power in four states as Isaac, now a tropical storm, continues to pummel the Gulf Coast with rain and maximum sustained winds of 70 mph.
Forecasters at NOAA are warning that Isaac could create "life-threatening hazards from storm surge and inland flooding as it moves slowly across southeastern Louisiana."
An unofficial rainfall total of 22.5 inches was reported in Arabi, La., near the city's 9th Ward. An official report from Audubon Park in New Orleans listed 17 inches of rainfall.
Three helicopters were in the New Orleans area in case residents needed to be rescued from floodwaters. Each crew was equipped with hoist capability and a rescue swimmer, according to Coast Guard officials.
Hurricane Isaac weakened into a tropical storm Wednesday afternoon -- but not before its powerful storm surge overtopped levees, raising water levels as far as 314 miles up the Mississippi River.
Hurricane warnings were discontinued as the storm moved northwest at 6 mph. A tropical storm warning was in effect from Cameron, La., to the Alabama and Florida border.
Despite the downgrade, forecasters said Isaac wasn't running out of steam just yet.
Six- to 12-foot storm surges were expected in Mississippi and southeastern Louisiana, with seven to 14 inches of rainfall.
The Central Gulf Coast region and part of the Lower Mississippi Valley could experience tornados through Thursday.
Isaac, which at its peak was a weak Category 1 hurricane, showed storm surge heights more characteristic of a strong Category 2 storm. The hurricane overtopped levees, knocked down trees and cut power to 716,068 in Alabama, Florida, Louisiana and Mississippi
There were no reports of injuries but dozens of residents of Plaquemines Parish, La., were stranded atop a levee, while there were multiple reports of people trapped in attics by rising waters.
As of mid-afternoon, fewer people had been evacuated than during Hurricane Katrina, which hit New Orleans seven years ago Wednesday.
A total of 56 parishes in Louisiana declared states of emergency, according to Louisiana Gov. Bobby Jindal, who added that there was a breakaway of a non-federal levee on the East Bank in Plaquemines Parish. The parish had a mandatory evacuation at noon Tuesday. Officials were considering conducting an intentional breach to release some of the water at that levee.
Thousands who live in the area were stuck in their homes or attics, and rescuers were out in boats helping those who needed it most.
There were 19 parishes included in the federal disaster declaration, while approximately 8,200 national guardsmen were available to help with search-and-rescue efforts, according to Gov. Jindal. There were 4,130 people in shelters across the state -- 730 in state-run shelters and 3,237 evacuees in parish-run shelters, according to Jindal.
In advance of the storm, Louisiana set up shelters and stockpiled more than a million packaged meals, 1.4 million bottles of water and 17,000 tarps.
Since the levees failed in Katrina seven years ago, more than $14 billion has been spent on the 133 miles of floodwalls, spillways, gates and pumps surrounding New Orleans.
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