Hurricane Isaac is dumping heavy rains and battering the northern U.S. Gulf Coast with strong winds as it slowly crawls ashore and heads toward New Orleans, seven years to the day that Hurricane Katrina devastated the city.

The U.S. National Hurricane Center says the center of the storm will remain over the state of Louisiana through Thursday and move over the neighboring state of Arkansas by early Friday.

Forecasters said Wednesday morning that Isaac had weakened slightly, but still is packing 120-kilometer-per-hour winds and areas along the coast are facing dangerous storm surges and flooding rains. More than a half million people were left without electricity.

Emergency officials in Plaquemines Parish, southeast of New Orleans, are reporting “significant flooding” as the storm pushes water in from the Gulf of Mexico and over the top of the area's levees. But the federal government said that New Orleans' flood barriers reinforced since Katrina have so far withstood the onslaught from Isaac.

Isaac's rainfall could total 50 centimeters in some places, and parts of Louisiana and Mississippi could see storm surges as high as four meters.

Mississippi Governor Phil Bryant warned residents of the storm's life-threatening dangers.

''This is a very dangerous storm and with those waters rising as quickly as they could be, a loss of life is a very real possibility.''

For Gulf Coast residents, Hurricane Isaac's arrival was a reminder of the more powerful Hurricane Katrina in 2005. Katrina killed 1,800 people in the region and caused massive damage, some of which remains today.

U.S. President Barack Obama declared states of emergency for Louisiana and Mississippi, making both states eligible for federal funding and other aid. Emergency assistance teams were dispatched to the region in advance of the storm.