New Orleans officials have warned city residents to stock up on supplies and prepare to shelter in their homes as "life-threatening" Tropical Storm Barry is poised to come ashore.
The tempest does not yet have hurricane-force winds but it is forecast to bring torrential rains of up to 64 cm in certain places, which officials say risk flooding along the already-swollen lower Mississippi River.
"Tropical Storm Barry is a dangerous and life-threatening storm," National Weather Service meteorologist Benjamin Schott warned a news conference on Friday. "Major to ... record flooding will be possible."
Officials cancelled a Sunday night concert by the Rolling Stones. Residents were ordered to evacuate some nearby areas but the New Orleans mayor said no evacuations were ordered from the low-lying city which strengthened its flood defences after devastating Hurricane Katrina in 2005.
US President Donald Trump declared a state of emergency for Louisiana and the region's oil production was cut in half as energy companies evacuated offshore drilling facilities.
Barry packed maximum sustained winds of 100km and hour on Friday morning and was centred 160km southwest of the mouth of the Mississippi River.
Barry will likely strengthen into a hurricane, the National Hurricane Center said, with winds of at least 119km, by the time it reaches the central Louisiana coast on Saturday.
It was forecast to bring a coastal storm surge into the mouth of the Mississippi River that winds through the heart of New Orleans, pushing its crest to 5.79m on Saturday. That would be the highest since 1950 and dangerously close to the top of the city's levees.
New Orleans is already saturated after torrential rains flooded streets on Wednesday.
"If it's worse than the other day, it'd be the worst week since Katrina," said Robert Harris, 61, as he polished his trombone while sitting in a folding chair on a footpath.
Memories of that storm, which flooded much of the city and killed 1800 people, are deeply embedded in New Orleans.
The brunt of Barry is expected to skirt the western edge of New Orleans, avoiding a direct hit.
Mayor LaToya Cantrell said 48 hours of heavy downpours could overwhelm pumps designed to purge streets and storm drains of excess water.
"There is no system in the world that can handle that amount of rainfall in such a short period," Cantrell said on Twitter.
Officials from the US Army Corps of Engineers, which maintains the levees, insisted that no significant breaching of the 6m-tall levees in New Orleans was likely.
New Orleans residents who plan to ride out the storm flocked to supermarkets for bottled water, ice, snacks and beer, thronging grocery stores in such numbers that some ran out of shopping carts. Throughout the city, motorists left cars parked on the raised median strips of roadways hoping the extra elevation would protect them from flood damage.
Australian Associated Press