Flooding had already begun overnight on Friday with reports of high water over roads and stranded vehicles.
Tropical weather system in the Gulf of Mexico
The National Hurricane Center in Miami said in a 4am (08:00 GMT) advisory that the storm was located 45 miles (75km) southwest of New Orleans with maximum sustained winds of 45mph (75km/h).
Flooding had already begun overnight on Friday with reports of high water over roads and stranded vehicles. Flash flood warnings dotted the coast while flood watches were in effect well inland for parts of Mississippi, Alabama, Florida, and central and northern Georgia.
The storm, churning northward in the Gulf of Mexico, is likely to dump anywhere from five inches (13cm) to 10 inches (25cm) of rain along with parts of the Gulf Coast and even 15 inches (38cm) in isolated areas, according to forecasters at the National Hurricane Center.
In Louisiana, the threat came a month after spring storms and flooding that were blamed for five deaths, and as parts of the state continued a slow recovery from a brutal 2020 hurricane season.
That included Tropical Storm Cristobal that opened the season last June, hurricanes Laura and Delta that devastated southwest Louisiana, and Hurricane Zeta that downed trees and knocked out power for days in New Orleans in October.
Mexico, while getting rain from the storm in the Gulf, also was threatened by a storm in the Pacific. Tropical Storm Dolores formed on Friday with landfall expected on its west-central coast on Saturday evening, possibly near hurricane strength, according to the National Hurricane Center.