Hurricane watches were issued for parts of Cuba and Mexico on Monday as a cluster of storms located south of the Cayman Islands was expected to strengthen into a major hurricane in upcoming days while moving north toward the U.

The National Hurricane Center says the disturbance could be at least a Category 3 when it reaches the northeastern Gulf Coast on Thursday.

A tropical disturbance brewing in the Caribbean Sea could become the strongest hurricane to hit the U.S. this year, according to forecasters. The storm — identified Monday as Potential Tropical Cyclone Nine by the National Hurricane Center — would be named Hurricane Helene and could hit the Florida Panhandle by Thursday morning.