Thu Oct 3, 8:46 PM ET

By Ned Randolph

NEW IBERIA, La. (Reuters) - Hurricane Lili swept across southern Louisiana on Thursday, cutting a path of destruction through Cajun country, then weakened into a tropical storm as it moved inland.

It knocked over trees, blew out windows and downed power lines as it raced along, but its impact was greatest on U.S. energy supplies. No storm-related deaths had been reported.

Lili, which came on the heels of Tropical Storm Isidore last week, temporarily curtailed virtually all oil production in the Gulf of Mexico, the U.S. Minerals Management Service said.

The oil shortfall in the gulf, which provides 25 percent of U.S. energy, forced a Williams Cos. Inc. refinery in Memphis, Tennessee, to borrow 500,000 barrels of crude from the nation`s Strategic Petroleum Reserve on Wednesday, the Department of Energy said.

Lili began the day as a fearsome Category 4 storm roaring out in the gulf with 145 mph winds. But it crossed cooler waters on the way to shore, lost its punch and hit the coast with 100 mph winds that quickly fizzled.

By Thursday afternoon, Lili`s winds had dropped to 50 mph, making it just a tropical storm as it trekked north, the National Hurricane Center in Miami said.

The center said Lili would likely fall to tropical depression status, with winds below 39 mph later on Thursday. It was expected to turn northeast and be in New England by the weekend.

Earlier in the day, Lili became the first hurricane to hit the U.S. since Irene struck Florida in 1999 when it whipped into Cajun country along the central Louisiana coast. It raked New Iberia, 150 miles west of New Orleans, with 92 mph wind gusts that sent debris flying and toppled huge trees onto houses and roadways.

Television shots showed entire sides of metal buildings tumbling along in the wind and a horse struggling to keep from getting blown over in Abbeville, west of New Iberia.

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