Tropical Storm Barry is churning in the Gulf of Mexico on Thursday as the dangerous storm nears the coast, threatening to bring heavy rain, flash flooding and storm surge.
Tropical storm conditions are expected in Louisiana on Friday and hurricane warnings were issued for southeastern parts of the state. The storm is expected to make landfall late Friday into early Saturday.
"This is going to be a major weather event for a huge portion of the state," Louisiana Gov. John Bel Edwards warned Thursday.
Louisiana's Plaquemines Parish and Grand Isle are already under mandatory evacuations.
In Lafitte, Louisiana, residents rushed to fill up sandbags.
Heavy rains already inundated New Orleans on Wednesday, flooding streets and homes and leaving drivers stranded. As much as 9 inches of rain fell in the city, with more to come.
New Orleans Mayor LaToya Cantrell declared a state of emergency in the city, but the city has not issued evacuation orders; Cantrell said Thursday, "sheltering in place is our strategy."
Residents are encouraged to store 72 hours' worth of food, water and medication for everyone in the home, including pets.
New Orleans Fire Department officials urged residents to pack emergency items in the event of a last-minute evacuation.
"We have to be prepared for all impacts," the mayor said.
Immigration enforcement has been suspended through the weekend in Louisiana and Mississippi areas impacted by the storm, New Orleans officials said.
"The city of New Orleans, our residents, should not be affected by ICE at all," the mayor said. "We want them to be protected, we want them to be safe."
The main concern is how much water the storm is forecast to bring, from the heavy rain to storm surge.
As much as 20 inches of rain is possible, especially in southern Louisiana, and because the storm is especially slow-moving, the rain will extend inland, flooding the Mississippi River Valley.
Storm surge warnings have been issued for the southeast Louisiana coast, where life-threatening inundation could reach 3 to 6 feet from the mouth of Atchafalaya River to Shell Beach.
A storm surge watch was issued elsewhere along the Louisiana and Mississippi coasts, where the surge may reach 4 feet in some areas.
The Mississippi River in New Orleans is expected to crest at 19 feet, and the levees in New Orleans are 20 to 25 feet -- so this is good news for the city, a spokesman for the U.S. Army Corps of Engineers told ABC News.
But as the forecast may still change, this will be a major test of the city's levee systems.
Gov. Edwards has requested a federal emergency declaration.
ABC News' Stephanie Ebbs, Brandon Baur and Rachel Katz contributed to this report.