|The storm has a 50-60 per cent chance of turning into a hurricane, according to a meteorologist [AFP]
Tropical Storm Lee is threatening the Louisiana coast amid torrential rains and flooding that have nearly shut half of US offshore crude oil production and a third of offshore gas production.
The slow-moving storm, which started on Friday, is expected to reach the Louisiana coast early on Sunday and bring 10-15 inches (25-38 cm) of rain to southeast Louisiana over the weekend.
The US National Hurricane Center said areas at risk include low-lying New Orleans, which was battered by Hurricane Katrina in 2005.
Lee was about 295km southwest of the Mississippi River's mouth, with maximum winds of 75kph, the hurricane centre said.
Its heavy rain and gusty winds were already buffeting the Louisiana coast, it said.
Bobby Jindal, Louisiana's governor, warned that heavy rains,substantial winds and tidal surges from the Gulf of Mexico could produce flash flooding in parts of New Orleans throughout the Labour Day holiday weekend.
"Get ready for the wind, get ready for the rain, it's coming and it's going to be here for a while," Jindal said at a briefing in Baton Rouge, the capital.
Jindal has declared a state of emergency for Louisiana, and Mississippi governor Haley Barbour made a similar ruling for seven coastal counties.
Lee has a 50-60 per cent chance of reaching hurricane strength, Bernie Rayno, a senior meteorologist with AccuWeather, told Reuters Insider.
"The problem with this system is that it's so slow-moving," Rayno said. "The big story is going to be the flooding."
Major offshore producers like Royal Dutch Shell, Exxon Mobil Corp and BP Plc shut down platforms and evacuated staff earlier this week.
Last week Hurricane Irene lashed the east coast and New York, killing dozens of people and knocking out power lines for millions of people.