[Editor’s note: This story was updated from a previous version posted at 3:15 p.m. CT Aug. 21.]

Energy firms shut 57.6%, or 1.07 million bbl/d, of offshore crude oil production in the U.S. Gulf of Mexico (GoM) because of the twin threat from Hurricane Marco and Tropical Storm Laura, the U.S. government said on Aug. 23.

Also, 44.6%, or 1,205 MMcf/d, of natural gas output was shut ahead of the storms, the federal Bureau of Safety and Environmental Enforcement (BSEE) said.

Workers have been evacuated from 114 production platforms out of the 643 manned platforms in the GoM, BSEE said.

Hurricane Marco and Tropical Storm Laura, also expected to become a hurricane, are poised to make back-to-back landfalls along the central Gulf Coast by mid-week. It is rare to have two simultaneously spinning in the Gulf and has raised concerns of double-barrel hits to coastal communities.

However, neither storm is expected to become a major hurricane, and their potential tracks cover a wide area of the Gulf Coast, said forecasters.

Murphy Oil Corp. and BHP Group Plc on Aug. 22 were evacuating some workers and Royal Dutch Shell Plc began shutting oil and gas production at most of its offshore operations. Murphy was making plans for possible production cuts, the company said.

Equinor ASA has finished evacuating its Titan oil-production platform in the U.S. GoM ahead of twin storms moving into the region, a spokesman said Aug. 23. The company also shut-in oil production at the facility, which is about 65 miles (105 km) off the coast of Louisiana.

BP Plc and Chevron Corp. began production shutdowns on Aug. 21. Occidental Petroleum Corp., the third largest Gulf of Mexico offshore producer, said it was implementing weather-related procedures.

Producers halted 240,785 bbl/d of oil and 119 MMcf/d of natural gas output before noon on Aug. 22, BSEE said. Crews were evacuated from six production and four drilling rigs. Another seven drilling vessels were moved out of the storms' paths, BSEE reported.

On Aug. 22, Marco was packing 65 mile per hour (100 km/h) winds, and was expected to become a Category One hurricane before making landfall in southeast Louisiana on Aug. 24. Storm Laura is expected to become a Category One hurricane and reach the northern Gulf Coast a day or two after Marco.

"We don't see the intensity and strengthening risk," said Matt Rogers, president of Commodity Weather Group, which advises energy and agricultural firms. The prospect of either becoming a damaging, Category Three storm is just 10%, he said.

Unlike Hurricane Harvey, which struck the region three years ago, neither is expected to linger inland, he said, reducing risk of coastal flooding.

Helicopters on Aug. 22 were crisscrossing the GoM, ferrying workers off platforms in precautionary measures, said Tony Hermans, base manager at Bristow Galliano heliport in southern Louisiana. Scheduled evacuations will be completed by Aug. 23, he said.

U.S. GoM offshore wells account for 17% of total U.S. crude oil production and 5% of total U.S. natural gas production. The region along the Texas to Mississippi coasts also accounts for 45% of total U.S. petroleum refining capacity.

Louisiana Offshore Oil Port, a major oil export and import terminal, reported it had begun implementing weather procedures.

Offshore