The season's first Atlantic hurricane is disrupting cleanup of BP's massive oil spill in the Gulf of Mexico.
Alex is delaying plans to boost containment capacity and threatening to push more oily water onshore.
The Gulf oil spill disaster has reached day 72, with environmental and economic costs to tourism, wildlife, fishing and other industries still mounting and the future of the energy giant far from clear.
Local residents are braced for heavy rains and flooding from Alex, which strengthened into a hurricane late last night.
The storm was on track to make landfall near the Texas-Mexico border late today.
Swathes of southern Louisiana and Mississippi are under flood watches, while coastal areas are also seeing unusually high tides.
With strong winds, waves as high as 4 metres and flooding rains on the way, controlled burns of oil on the ocean, flights spraying dispersant chemicals and booming operations are on hold for now, officials said.
The State Department said it would accept offers of help from a dozen countries and international agencies to contain and clean up the spill, including two high-speed skimmers and a fire containment boom from Japan.
Although Alex will not make a direct hit on oil platforms in the Gulf, the storm is potent enough that several companies have evacuated rigs.
About 25% of oil production and 9.4% of natural gas output in the Gulf of Mexico have been shut, US officials said.
The Atlantic hurricane season runs from 1 June to 30 Nov and meteorologists predict an active storm season.
Alex is the first June storm in 15 years to gain hurricane strength in the Atlantic.
