(Adds comments from Mississippi resident in paragraph 5, emergency official in paragraph 9 and loss of power)

By Jessica Resnick-Ault and Rod Nickel

NEW ORLEANS, Oct 7 (Reuters) - Hurricane Nate made landfall near the mouth of the Mississippi River as a Category 1 storm packing winds of 85 miles per hour on Saturday night, threatening parts of Louisiana, Mississippi and Alabama with torrential rain and potential flooding.

Nate, the fourth major storm to strike the United States in less than two months, killed at least 30 people in Central America before entering the warm waters of the Gulf of Mexico and bearing down on the U.S. South. It has also shut down most oil and gas production in the Gulf.

Nate comes on the heels of three other major storms, Harvey, Irma and Maria, which devastated Texas, Florida and Puerto Rico, respectively. But as a Category 1, the weakest in the five-category ranking used by meteorologists, Nate appeared to lack the devastating punch of its predecessors.

The National Hurricane Center (NHC) downgraded its warning for New Orleans to a tropical storm. But Nate was expected to regain some strength and make a second landfall along the coast of Mississippi to the east.

"The only thing you can do is prepare," said Gulfport, Mississippi, resident Emmett Bryant. "Here there's nothing really you can do when the storm comes unless you're going to leave. And I don't plan on leaving."

The hurricane's center was expected to pass over portions of Mississippi, Alabama, and Tennessee late Saturday through Sunday night, eventually weakening to a tropical depression. Before then, storm surges of up to 11 feet (3.4 m) on the Mississippi-Alabama border were still possible, the NHC said.

The center of Hurricane Nate was expected to make landfall on the Mississippi Coast by midnight on Saturday and weaken significantly, the NHC said.

The storm was about 60 miles (95 km) east of New Orleans with a maximum sustained winds of 85 mph (140 km per hour), the center said.

In Hancock County, Mississippi, northeast of New Orleans, rain and wind were gaining intensity and many streets were washing over. Conditions are likely to worsen in the next few hours, said Brian Adam, director of emergency management for the county.

The county evacuated people from low-lying areas and imposed a curfew.

Earlier in the day, states of emergency were declared in Louisiana, Mississippi and Alabama, as well as in more than two dozen Florida counties.

In a statement, the City of Biloxi, Mississippi, warned its 46,000 residents that the highest storm surge would occur between 10 p.m. and 3 a.m. and could reach 11 to 12 feet.