At least three people have died as a result of the storm.
Ida is barreling through Louisiana after making landfall in the state as a powerful Category 4 hurricane on Sunday afternoon.
It was one of the strongest hurricanes on record -- by both wind speed and pressure -- to roar ashore in Louisiana.
Ida, now a tropical storm, is hitting on the 16-year anniversary of Katrina, a Category 3 hurricane that ravaged the Gulf Coast. Hurricane Katrina unleashed a series of events, taking the lives of more than 1,800 people and leaving more than $100 billion worth of damage in its wake.
AT&T said its Louisiana wireless network is operating at 60%.
"We had key network facilities go offline overnight, and while some have already been restored, some facilities remain down and are inaccessible due to flooding and storm damage," AT&T said in a statement.
-ABC News' Alexandra Faul
New Orleans residents who evacuated their homes should not return until further notice, the New Orleans Office of Homeland Security and Emergency Preparedness said.
"There is widespread debris, power remains out, and emergency services are working to respond to those still in the city," city officials said. "We will let you know when it is safe to come home."
The Louis Armstrong New Orleans International Airport is conducting damage assessments and said it expects all flights to be canceled Monday.
The airport added that passengers should check directly with their airlines for more information.
So far New Orleans' airport has 118 canceled flights. Some flights have also been canceled in Houston, Dallas, Pensacola and Atlanta.
-ABC News' Alexandra Faul, Amanda Maile
Power could be out for weeks in the areas hit hardest by Ida, Entergy said Monday.
"Where weather permitted, our crews were out at first light today assessing damage where it was safe to do so," the energy company said in a statement. "This will help us get a better idea of what we’re dealing with. It would be premature to speculate at this time when power will be restored given the extent of the damage."
The ability to reach some areas is hindered by road closures and flooding, the company said.
"In harder to reach areas, we use advanced technology, such as infrared cameras, drones and satellite imagery to assess damage by foot, vehicles, airboats, highwater vehicles and helicopters. Even so, lack of access in areas like waterways and marshes could delay our damage assessment," Entergy said.
-ABC News' Josh Hoyos
