Tropical storm Helene expected to become hurricane as it heads for US

Sandbags are filled at a public site while residents prepare their homes for potential flooding in Tarpon Springs, Florida as Tropical Storm Helene approaches (Douglas R. Clifford/AP)

Tropical Storm Helene which formed in the Caribbean Sea could strengthen into a major hurricane while moving north toward the US, forecasters have said.

Heavy rains and big waves already lashed the Cayman Islands, and some Florida residents filled sandbags days ahead of anticipated flooding.