Tropical depression Harvey is headed for Texas and could develop into a hurricane just before landfall.
Harvey, which could become the first hurricane to strike Texas since 2008, has forced workers to be evacuated from Gulf of Mexico platforms.
Harvey was 755km southeast of Port Mansfield, Texas, with top winds of 55 km/h, the US National Hurricane Centre said in an advisory.
"It could intensify right up to landfall on [Saturday NZT]," said Jeff Masters, co-founder of Weather Underground in Ann Arbor, Michigan. "I expect a Category 1 hurricane at landfall, but I cannot rule out a Category 2."
The Gulf Coast from Corpus Christi, Texas, to Lake Charles, Louisiana, is home to nearly 30 refineries - making up about 7 million barrels a day of refining capacity - and is in the path of heavy rainfall. Flooding poses risks to operations, while torrential rains can shut units and cause supply disruptions.