Nate was downgraded to a tropical depression after twice making US landfall.

Nate strengthened to a Category 1 hurricane on Friday night, according to the National Hurricane Center.

The storm has killed at least 22 people in Central America.

All coastal watches and warnings have been discontinued.

Nate was downgraded Sunday afternoon to a tropical depression with maximum sustained speeds of 35 mph, less than two days after becoming a Category 1 hurricane. The storm was expected to soak the deep south with heavy rainfall as it moves inland across the Tennesse Valley and Central Applachian Mountains, according to the National Hurricane Center's 10 a.m. CDT update.

All coastal watches and warnings have been discontinued, but Nate was expected to turn toward the northeast in the next couple of days, the National Hurricane Center said, and could gain speed in the interim.

Nate has already been blamed for at least 22 deaths across Nicaragua and Costa Rica, The Associated Press reported, and it's causing dangerous flooding and landslides.

Nate skimmed the coast of Mexico's Yucatan Peninsula Friday night before heading for the US Gulf Coast.

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In preparation for the storm, officials in Louisiana ordered residents living along part of the east coast of New Orleans and in other areas near the coast to evacuate. States of emergency have been declared for New Orleans and other parts of Louisiana and for parts of Mississippi, Alabama, and Florida.

New Orleans Mayor Mitch Landrieu declared a mandatory curfew from 6 p.m. Saturday night through Sunday morning.

Houses damaged by a mudslide are seen during heavy rains of Tropical Storm Nate that affects the country in San Jose, Costa Rica October 5, 2017. REUTERS/Juan Carlos Ulate

Bracing for flooding

As of Friday night, Nate's hurricane-force winds had maximum sustained speeds of 75 mph, with gusts going higher than that.

Hurricane warnings have been issued for the Gulf Coast from Grand Isle, Louisiana, to Alabama's border with Florida and for metropolitan New Orleans and Lake Pontchartrain.

Hurricane watches — meaning hurricane conditions may arrive within two days — are in effect from east of Alabama's border with Florida to the Okaloosa/Walton County line in Florida; from west of Grand Isle to Morgan City in Louisiana; and Lake Maurepas.

Storm surge warnings — meaning the storm is likely to raise water levels significantly — are in effect from Morgan City, Louisiana, to the Okaloosa/Walton county line in Florida, and for the northern and western shores of Lake Pontchartrain.

The New Orleans branch of the National Weather Service said the "storm surge warning indicates the danger of life threatening inundation."

Nate was expected to pour 15 to 20 inches of rain onto much of Nicaragua, with isolated locations getting 30 inches. Authorities closed all schools and placed the entire country on alert, according to the AP. In Costa Rica, 5,000 people fled to emergency shelters.

On much of the Gulf Coast, Nate is expected to dump three to six inches of rain, with some areas getting 10 inches.

NOAA

Rapid strengthening possible

It's hard to predict the exact path and intensity that Nate will have by the time it nears the Gulf Coast, especially since the storm is still relatively disorganized. But the water that Nate is moving over now is extremely warm, which means conditions are ripe for rapid strengthening.

Nate is expected to become a hurricane before it reaches the northern Gulf of Mexico. Forecasters caution that the strength and category of a storm are not necessarily reflective of the damage it can cause, as heavy rainfall and storm surge can be destructive even without extreme winds.

—The Weather Channel (@weatherchannel) October 6, 2017

Nate adds yet another threat to what has already been an extremely active Atlantic hurricane season. It's the 14th named storm of the season, which doesn't end until late November.

So far this season, we've had eight hurricanes, five of which were major hurricanes — classified as Category 3 or above. If Nate's wind speeds pick up, it will be the ninth.

The western Caribbean, where Nate formed, is one of the main spots to watch for storms at this point in the season, according to Phil Klotzbach, a meteorologist at Colorado State University. Since 1851, 25% of Atlantic tropical storms, 33% of hurricanes, and 60% of major hurricanes in October have formed in that region.