Tropical Storm Debby formed in the central Gulf of Mexico on Saturday and was expected to strengthen into a hurricane as it skirted the Louisiana coast and took aim at Texas, the US National Hurricane Center said.

Debby covered much of the eastern Gulf and was centered about 215 miles (346 km) south-southeast of the mouth of the Mississippi River. The storm had top winds of 50 miles per hour (81 km per hour) and was expected to strengthen into a hurricane by Tuesday night.

The storm was nearly stationary but was forecast to start drifting north by Monday and then turn west, grazing the Louisiana coast through Tuesday and slamming into Texas late in the week.

Oil and gas producers evacuated workers from oil and gas platforms and shut in production on Saturday as the weather worsened in the Gulf of Mexico, which is home to 20 per cent of US oil production and 6 per cent of natural gas output.

The US Bureau of Safety and Environmental Enforcement, which oversees oil and gas activity in the Gulf, said earlier on Saturday that 7.8 per cent of daily oil output and 8.16 per cent of daily natural gas output were shut down.

The agency's next update will be released at midday on Sunday.

A tropical storm warning was issued for the Louisiana coast from the Pearl River west to Morgan City, excluding the city of New Orleans and Lake Pontchartrain. Residents were warned to expect storm conditions within 36 hours.

"Tropical storm conditions are expected to first reach the coast within the warning area by Sunday night, making outside preparations difficult or dangerous," the forecasters warned.

The combination of storm surge and high tide could cause flooding in normally dry areas near the Louisiana coast, they said.

Debby could bring 3 to 6 inches (8 to 15 cm) of rain to the Gulf Coast from southern Louisiana to the Florida Panhandle, with up to 10 inches (25 cm) of rain in isolated areas.

The heaviest squalls were hitting Florida's Gulf Coast, where there were unconfirmed reports that a tornado had touched down on Saturday. Several Alabama beaches were closed due to rough surf.

Forecasting models still diverged on the storm's potential path. Most swung it west toward Texas or Louisiana, but a few still took it east toward Florida. – Reuters