"A Hurricane Warning is now in effect for the coast of Louisiana from Intracoastal City to Grand Isle," the statement said on Thursday. "Tropical Storm Warning is now in effect for Lake Pontchartrain and Lake Maurepas, including metropolitan New Orleans."
The NHC said Tropical Storm Barry is forecast to affect hundreds of miles of southeastern Louisiana and southern Mississippi through the rest of this week and the weekend.
Widespread impacts to the area are expected including flooding, strong damaging winds and even a few weak or brief tornadoes, according to the alert. Maximum sustained winds were at least 40 miles per hour, the centre added.
On Wednesday, Louisiana Governor John Bel Edwards declared a state of emergency ahead of the storm that was brewing in the Gulf of Mexico.