Tropical Storm Helene formed Tuesday in the Caribbean Sea and could strengthen into a major hurricane while moving north toward the U.S., forecasters said. Heavy rains and big waves already lashed the Cayman Islands, and some Florida residents began to evacuate or fill sandbags ahead of anticipated flooding.

Tropical Storm Helene is expected to unleash mudslides and flooding in Cuba before reaching major hurricane strength on Thursday as it hits Florida with life-threatening ocean surge, the U.S. National Weather Service said.

Another storm system is taking aim at Florida, this time possibly the Panhandle with storm effects all along the Gulf Coast. Tropical Storm Helene, soon to be a hurricane, is sweeping up from the Caribbean Sea into extremely warm waters that are fuel for tropical cyclones.

Potential Tropical Cyclone Nine is expected to become Hurricane Helene on Wednesday, according to the National Hurricane Center.

Tropical Storm Helene formed over the northwestern Caribbean on Tuesday and triggered a tropical storm warning for the Lower Florida Keys. The storm is forecast to be a major hurricane for the Florida panhandle Thursday.

Florida residents are already evacuating and filling sandbags days ahead of anticipated flooding from Tropical Storm Helene