NEW ORLEANS (AP) - Hurricane Ida became a tropical storm as its top winds slowed over Mississippi on Monday, 16 hours after blowing ashore in Louisiana as one of the most powerful hurricanes ever to strike the U.S. mainland. Ida pushed so much water into the mouth of the Mississippi that it reversed the flow of the mighty river and blacked out New Orleans, taking down backup electricity for the city’s crucial pumping system.

Torrential rain kept falling Monday as the storm slowly moved north, with up to 2 feet expected in places, and reports of flooded roads and homes multiplied. Destructive winds and water already had a catastrophic impact along the southeast coast of Louisiana, and life-threatening river flooding continued well inland, the National Hurricane Center said.

Ida made landfall on the same day 16 years earlier that Hurricane Katrina ravaged Louisiana and Mississippi, and its 150 mph winds tied it for the fifth-strongest hurricane to ever hit the mainland. It was already blamed for one death, someone hit by a falling tree in Prairieville, outside Baton Rouge, deputies with the Ascension Parish Sheriff’s Office confirmed on Sunday.

More than a million customers in Louisiana and Mississippi were without power according to PowerOutage.US, which tracks outages nationwide, increasing their vulnerability to flooding and leaving them without air conditioning and refrigeration in sweltering summer heat.

Entergy confirmed that the only power in New Orleans was coming from generators, the city’s Office of Homeland Security & Emergency Preparedness tweeted, citing “catastrophic transmission damage.” The city relies on Entergy for backup power for the pumps that send stormwater over the city’s levees. The system is much-improved since Katrina, but Ida is posing its biggest test since that disaster.

The 911 system in Orleans Parish also experienced technical difficulties early Monday. Anyone needing emergency assistance was urged to go to their nearest fire station or approach their nearest officer, the New Orleans Emergency Communications Center tweeted.

Ida became a tropical storm again 16 hours after making landfall in Louisiana as a Category 4 hurricane. Its top sustained winds were 60 mph early Monday, and forecasters said it would rapidly weaken while dumping torrential rain over a large area. It was centered about 95 miles south-southwest of Jackson, Mississippi, moving north at 8 mph.

The rising ocean swamped the barrier island of Grand Isle and roofs on buildings around Port Fourchon blew off as Ida made landfall. The hurricane then churned through the far southern Louisiana wetlands, swirled over the state’s petrochemical corridor and threatened the more than 2 million people living in and around New Orleans and Baton Rouge.

Officials said Ida intensified into an extremely powerful hurricane too quickly over the Gulf of Mexico to organize a mandatory evacuation of New Orleans’ 390,000 residents. Many didn’t have enough gas and hotel money, transportation or other resources needed to flee. Hospitals also had no choice but to hunker down, counting on generators to keep COVID-19 patients alive.