Coastal Louisiana has felt the first blow from Tropical Storm Barry's winds as the slow-moving tempest was forecast to become the first Atlantic hurricane of 2019.
US President Donald Trump declared a state of emergency for Louisiana on Thursday, hours after the region's oil production was cut in half as energy companies evacuated offshore drilling facilities and a coastal refinery.
Tropical Storm Barry packed maximum sustained winds 85km/h early on Friday and was centred 155 km 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 119 km/h by the time it comes ashore late on Friday or early Saturday, but officials warned that torrential rains posed the greatest danger.
Authorities kept a close eye on the levee system built to contain flooding along the lower Mississippi River that winds through the heart of New Orleans and has been running above flood stage for the past six months.
Barry was forecast to bring a coastal storm surge into the mouth of the river that could push its crest to 5.79 metres on Saturday, the highest since 1950 and dangerously close to the top of the city's levees.
Meteorologists predicted as much as 64 cm of rain could fall, leading to life-threatening flooding along parts of the Gulf Coast on Friday and Saturday.
The brunt of the storm was expected to skirt the western edge of New Orleans, avoiding a direct hit.
Officials from the US Army Corps of Engineers, which maintains the levees, insisted that no significant breaching of the levees in New Orleans was likely.
Some residents, recalling the deadly, devastating floods unleashed by Hurricane Katrina in 2005, said they were determined to get out of harm's way.
Others 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.
A tropical storm warning was in place for metropolitan New Orleans, and a hurricane warning was issued for a stretch of the Louisiana coast south of the city.
Mandatory evacuation orders were issued for areas beyond the levees southeast of the city, and for low-lying communities to the southwest.
Australian Associated Press
