It has already impacted Honduras and Nicaragua and its expected trajectory will take it over Mexico's Yucatan peninsula near Cozumel and Cancun.
Once it reaches the open water of the Gulf of Mexico it could significantly strengthen, meteorologists say.
At least 22 are dead as a direct result of the storm in Nicaragua and Costa Rica due to flash flooding and landslides.
"Everyone in southeast Louisiana should start preparing for this storm now," said Louisiana governor John Edwards.
It will likely make landfall somewhere south of New Orleans, according to the latest forecasts.
"Areas from New Orleans across to the Florida Panhandle should be prepared for tropical conditions as the forecast will come into focus over approximately the next 36 to 48 hours," said NBC meteorologist Sherri Pugh.
Itineraries for the Carnival Triumph, Carnival Dream, Carnival Slendor and Carnival Sensation have been amended to steer clear of the storm, avoiding port calls in Cozumel.
Carnival Dream's scheduled return to New Orleans could be in doubt.
Royal Caribbean's Oasis of the Seas and Liberty of the Seas were also due to make port calls in Cozumel over the next few days.