Offshore crude production in the United States has fallen sharply as Hurricane Isaias advances toward a coastline dotted with refineries and chemical plants.

The U.S. National Hurricane Center said Isaias strengthened Thursday to a Category 2 storm on the Saffir-Simpson five-level hurricane scale, with more than 3 million residents in its projected path.

Hurricane wind speeds edged up slightly to 105 miles per hour (165 kilometers per hour), and the storm is forecast to make landfall late Friday or early Saturday along the Alabama coast or the Florida Panhandle.

In the National Hurricane Center's latest advisory, forecaster Brad Reinhart wrote that Isaias could briefly strengthen into a major hurricane early Friday, though it is expected to weaken afterward.

He added that the storm will still be a dangerous hurricane when it approaches the northern Gulf Coast later that day.

Oil companies are evacuating platform personnel and moving drilling rigs to safety, and Isaias drove U.S. crude prices up as much as 5.6% on Thursday.

About 63% of crude production capacity in the Gulf of Mexico has been shut in, and refining capacity of 500,000 barrels per day is under threat.

Several ports closed ahead of the hurricane, disrupting seaborne crude deliveries.

Three fuel production facilities sit on or near the hurricane's projected path, including Chevron's refinery in Pascagoula, Mississippi, which processes 356,000 barrels of crude per day.

U.S. gasoline and diesel inventories were already well below seasonal norms, so even a modest output cut could trigger a sharp jump in oil prices.

Natural gas production in the Gulf of Mexico has also declined, with about 57% of the region's gas production capacity shut in.