Mayor of New Orleans LaToya Cantrell has declared a state of emergency. Mandatory evacuation orders are being enacted elsewhere in Louisiana.
Tropical storm Barry is expected to make landfall late on Friday into Saturday morning (12-13 July), hitting coastal areas hard.
Thunderstorms and flash floods have already struck New Orleans, disrupting transport links - including flights.
"This is going to be a major weather event for a huge portion of the state," Louisiana governor John Bel Edwards has warned.
