"Look, there are three ways in which Louisiana is flooded: storm surge, high rivers and rain – we are going to have all three," said Gov. John Bel Edwards.
Barry crosses the Gulf of Mexico and is the first tropical storm to threaten the United States this year. Even if it is possible that the hurricane reaches the level of a hurricane, the real threat posed by the storm is the rain – which could quickly turn into an unprecedented flood.
It moves slowly in the warm waters of the Gulf of Mexico, giving it time to strengthen and is expected to cause significant rainfall to some 10 million people in its path.
The Mississippi River, which is typically 6 to 8 feet around New Orleans at this time of year, is 16 feet after a record year of flooding. And 10-15 inches of extra rain are on the way, said CNN meteorologist Derek Van Dam.
By early Friday, Barry was 95 miles southwest of the mouth of the Mississippi with maximum sustained winds of 50 mph.
Preparations and evacuations
President Donald Trump has declared the state of emergency in Louisiana, where the storm is expected to land.
Louisiana has activated 3,000 members of the National Guard in anticipation of the destruction that Barry could cause in the area, said the governor.
Officials expect to issue a mandatory Friday evacuation order for everyone south of the Leon Theriot floodgate. But many locals are not too eager to leave.
Pamela Hughes said she was crossing the storm in her mother's caravan at Port Sulfur, which is the subject of a mandatory evacuation order.
"I really do not think it will be too bad," she told CNN.
Others, like Kristopher Williams, stay put to protect their animals and their property.
"All I own is in it," he says of his truck. "I'm not an ignorant person, I know the dangers, and I know how to get out of all the obstacles I encounter."
A hurricane warning is in effect for Intracoastal City to Grand Isle and hurricane monitoring is in effect for the mouth of the Mississippi River towards Grand Isle.
Pumps and pipes overflowed
New Orleans' pump, duct and canal system has been inundated by rains earlier this week, but Edwards said Thursday that, according to current forecasting models, the Mississippi River should not exceed the level of the river.
There is a good chance Tropical Storm Barry will reach winds of 120 km / h and turn into a hurricane. More than 800,000 people are currently under the warning of a hurricane.
Flooding concerns are not limited to Louisiana and have spread to the Gulf region.
Mississippi, Alabama and western Florida are also threatened by extreme rainfall, CNN meteorologist Haley Brink said Thursday.
In addition to potential heavy rains in Louisiana, the Mississippi Delta region is also exposed to tornadoes starting Friday night.
CNN's Holly Yan, Brandon Miller, Paul P. Murphy, Darran Simon and Dakin Andone contributed to this report.