NWS forecasters in New Orleans said in a 5:22 p.m. CDT advisory that warning area included Assumption, Upper Lafourche, Upper Terrebonne, Lower Terrebonne, Lower Lafourche, Lower Jefferson, Lower Plaquemines and lower St. Bernard.
The weather service said the warning included marine interests off the coasts of southeast Louisiana and Mississippi.
At 5 p.m., the center of Debby was about 310 miles south-southeast of New Orleans and about 300 miles south-southeast of Gulfport, Miss.
Debby was heading to the north at 6 mph and was producing 50 mph winds.
The weather service said the storm's primary threat would be coastal flooding and lakes on the Louisiana coast. Roads and low-lying areas outside the hurricane protection levees will experience flooding, the forecasters said.
The weather service advised ports, docks and marinas to complete their preparations according to their emergency operations plans. Those living aboard boats were told to secure their crafts before leaving them and small boats have been advised to remain in port.
Those living in mobile homes in the warning area were advised to seek more substantial shelter.
Debby's winds are expected to slowly increase over the next couple of days and peak Monday through early Tuesday.