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.

Helene is expected to rapidly intensify into a major and massive hurricane with 115-mph winds by the time it makes landfall Thursday.

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.