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 was rapidly strengthening in the Caribbean Sea and expected to become a hurricane Wednesday while moving north along Mexico’s coast toward the U.S.

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