Forecasters say they expect Tropical Storm Helene in the Caribbean Sea to strengthen rapidly and become a hurricane as it moves north across the Gulf of Mexico on Wednesday toward the U.S.

Tropical Storm Helene formed in the northwestern Caribbean Sea on Tuesday, but National Hurricane Center forecasters expected the storm to quickly turn into a hurricane by Wednesday as it enters the unusually warm waters of the Gulf of Mexico.

As Tropical Storm Helene approaches, airlines are issuing waivers for those who may need to change their travel plans. Here's what to know.