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.

Helene is expected to make landfall in the Big Bend region of Florida on Thursday evening after traveling northward over the Gulf of Mexico over the past two days. At 1 a.m. ET on Wednesday, Helene was situated approximately 65 miles east of Cozumel, Mexico, and 120 miles southwest of the southern tip of Cuba.

Tropical storm conditions are expected in southern Florida later today and spreading northward through Thursday.