Almost 800 rescued in St. John the Baptist Parish after Hurricane Ida

About 16 hours after making landfall in Louisiana, Ida was downgraded from a hurricane to a tropical storm early Monday morning.

As of 4 a.m. CT, Ida was moving north at 8 miles per hour with the eye of the storm located about 95 miles south-southwest of Jackson, Mississippi, and 50 miles north-northeast of Baton Rouge, Louisiana. The storm's maximum sustained winds have decreased near 60 miles per hour with higher gusts, according to an advisory from the National Weather Service.

The storm surge warning has been discontinued from Morgan City to Grand Isle, Louisiana. The hurricane and tropical storm warnings have been discontinued west of Grand Isle. The hurricane warning has been replaced with a tropical storm warning from Grand Isle to the mouth of the Pearl River, including Lake Pontchartrain, Lake Maurepas and metropolitan New Orleans. Storm surge and tropical storm warnings remain in effect for Grand Isle to the Alabama-Florida border, according to the National Weather Service.

Meanwhile, 16 states from Mississippi to New Jersey are still on alert for flash flooding. A flash flood watch is in place from the Gulf Coast to New Jersey.

So far, the highest rainfall total was recorded in LaPlace, Louisiana, which received 15 inches. A flash flood emergency remains in effect there, according to the National Weather Service.

Ida is forecast to rapidly weaken even more over the next day or so, becoming a tropical depression by Monday evening.

The storm will move farther inland over southeastern Louisiana early Monday and into southwestern Mississippi later in the morning. Ida is then forecast to move over central and northeastern Mississippi on Monday afternoon and evening before moving across the Tennessee Valley on Tuesday, according to the National Weather Service.

-ABC News' Max Golembo

The National Weather Service has issued a tornado warning for eastern Harrison County and northwestern Jackson County, both in southern Mississippi.

As Hurricane Ida approaches the Magnolia State, a severe thunderstorm capable of producing a tornado was located via radar over Biloxi in Mississippi's Harrison County early Monday at 2:46 a.m. CT. The "tornadic thunderstorm" was moving north at 65 miles per hour, according to an alert from the National Weather Service, which urged people to "take cover now!"

"Move to a basement or an interior room on the lowest floor of a sturdy building. Avoid windows," the National Weather Service said. "If you are outdoors, in a mobile home, or in a vehicle, move to the closest substantial shelter and protect yourself from flying debris."

The storm could impact the Gulfport–Biloxi International Airport as well as several miles of Interstate 10 and 110 in Mississippi, according to the National Weather Service. The tornado warning will remain in effect until 3:45 a.m. CT.

"Flying debris will be dangerous to those caught without shelter," the National Weather Service warned. "Mobile homes will be damaged or destroyed. Damage to roofs, windows, and vehicles will occur. Tree damage is likely."

-ABC News' Max Golembo

The emergency communications center for New Orleans said it is "experiencing technical difficulties" with its 911 system, after the city lost power due to Hurricane Ida.

"If you find yourself in an emergency, please go to your nearest fire station or approach your nearest officer," the Orleans Parish Communication District announced via Twitter early Monday. "We will update you once this issue has been resolved."

Ida has weakened to a Category 1 hurricane with maximum sustained winds of 75 miles per hour, as it continues to thrash Louisiana.

As of 1 a.m. CT, Ida was moving north at 9 miles per hour with the eye of the storm located about 20 miles south-southwest of Greensburg, Louisiana, and 45 miles from McComb, Mississippi, according to an advisory from the National Weather Service.

Ida is expected to continue heading north inland over southeastern Louisiana early Monday morning and later move into southwestern Mississippi, with further weakening forecast throughout the day. Ida is expected to be downgraded to a tropical storm later Monday morning, Nevertheless, the National Weather Service warned of continued threats from dangerous storm surge, damaging winds and flash flooding in parts of southeastern Louisiana.

In LaPlace, Louisiana, where up to 13 inches of rain has fallen from Ida so far, there were reports of high-water rescues to save residents trapped on top of homes amid completely flooded roads. The National Weather Service has extended a flash flood emergency for the area.

The National Weather Service also declared a flash flood emergency for Lafitte and Jean Lafitte, Louisiana, on Sunday night due to heavy rain and storm surge reportedly causing a levee to fail. Citing local law enforcement, the National Weather Service said more than 200 people were in "imminent danger" and urged people to "seek higher ground now!"

Heavy rainfall from Ida will continue Monday in southeastern Louisiana and spread northeast into the Lower Mississippi Valley. Total accumulations of 10 to 18 inches, with isolated maximum amounts of 24 inches, is possible across southeastern Louisiana into far southern Mississippi through Monday, according to the National Weather Service.

Storm surge, hurricane and tropical storm warnings remain in effect from Louisiana to the Alabama-Florida border. A tornado watch is also in place from Louisiana to the Florida Panhandle until 6 a.m. CT.

Ida is forecast to turn to the northeast on Monday and track across the Middle Tennessee Valley and Upper Ohio Valley through Wednesday, dumping rain throughout the region, according to the National Weather Service.

-ABC News' Max Golembo and Samantha Wnek