Strong winds and torrential rains from Tropical Storm Lee have knocked out power to thousands in the southern U.S. states of Louisiana and Mississippi Sunday.

Many low-lying areas prone to flooding have already been evacuated.

The National Hurricane Center says the slow-moving Lee could dump up to 50 centimeters of rain over southern parts of Louisiana, Mississippi and Alabama through Sunday. The storm is expected to be a serious test of the flood defenses of New Orleans, which suffered devastating damage in 2005 from Hurricane Katrina. The city's mayor has urged residents to prepare for the worst.

Lee's approach prompted oil and gas producers to shut down platforms and evacuate workers from the Gulf of Mexico.

Lee is the 12th named storm of the Atlantic hurricane season. It is hitting the United States just one week after deadly Hurricane Irene ravaged the nation's east coast.

Irene's winds and flooding devastated parts of the states of Vermont, Connecticut, New York, New Jersey and North Carolina. The storm caused billions of dollars in damage and is blamed for at least 45 deaths in the U.S. and five in the Caribbean.

U.S. President Barack Obama signed disaster declarations for New York, New Jersey and North Carolina, making federal funding available for recovery efforts. Mr. Obama is scheduled to visit New Jersey on Sunday to view wind and flood damage from Irene.

Meanwhile, in the Atlantic, Hurricane Katia weakened to a tropical storm Saturday, but the National Hurricane Center says Katia could return to hurricane status as it moves north of the Leeward Islands on Sunday.

September is normally the peak of the hurricane season. Experts predicted an active 2011 hurricane season with eight to 10 hurricanes possible, which would be slightly more than normal.