Tropical Storm Lee is heading closer to Louisiana, threatening to dump heavy rains and trigger dangerous flash floods along the Gulf of Mexico coast.
Oil companies evacuated workers from offshore rigs, while Louisiana's governor Bobby Jindal declared a state of emergency, urging residents to "prepare for the worst and hope for the best", AFP reports.
In New Orleans, much of which sits below sea level, Mayor Mitch Landrieu took similar measures. The storm will test the levees rebuilt after Hurricane Katrina pounded the region six years ago this week, CNN reports.
Mississippi Governor Haley Barbour declared a state of emergency in several counties, urging residents to be prepared.
"Do not underestimate the impact of this system of tropical weather," he said.
It was about 95 miles away from the Louisiana city early Saturday, CNN reports, packing winds of 50 miles an hour.
The current track suggests a possible landfall west of Morgan City on Sunday morning, CNN meteorologist Sean Morris said.
The storm was gaining strength early Saturday and inching northward at 5 mph. About 2 a.m. ET, it was 170 miles west-southwest of the mouth of the Mississippi River and had winds of 50 mph, the Hurricane Center reported.
Parts of southern Louisiana, Mississippi and Alabama could see 10 to 15 inches of rain by Sunday, with isolated totals of 20 inches, according to the hurricane center.
Lee could also bring isolated tornados, the National Hurricane Center in Miami has warned.
The biggest danger from Tropical Storm Lee -- the 12th named storm of the Atlantic season -- could be in the Appalachians, AFP reports.
"If we get the five to 10 inches that come out into a tropical storm in that kind of terrain, the flash flooding is fast and it's violent," Bill Read, director of the National Hurricane Center in Miami, told reporters.
The weather service is also monitoring the strengthening of Hurricane Katia, which had been downgraded to a tropical storm earlier in the week but regained hurricane status Friday after passing over warmer water, AFP reports.
Katia is still well out to sea, but several tracks show the hurricane possible aiming for the US eastern seaboard sometime next week.
The current hurricane could clip islands ringing the eastern Caribbean this weekend, with the NHC warning that Katia would send "life-threatening surf" barreling into the Lesser Antilles later Friday, AFP reports.