U.S., Aug. 24 -- Two dangerous weather developments are threatening the US Gulf Coast, two at a time.

Tropical stormMarcowas upgraded to hurricane status on Sunday as it gained strength over the Gulf of Mexico. Marco could be part of an unprecedented twin strike to the U.S. Gulf Coast alongside Tropical Storm Laura, which could also strengthen to a hurricane this week.

Marco entered the Gulf of Mexico Saturday evening and washeaded toward landfall in Louisiana or Mississippion Monday afternoon, according to National Hurricane Center projections.As of Sunday afternoon, the Air Force Reserve Hurricane Hunter found Marco had reached sustained winds of 75 mph.

To reachhurricane status, a storm needs to generate sustained winds of at least ...