"Helene stands toe-to-toe with any of the threats that Florida has faced over the past ten years or indeed really over hurricane history."

A shallow coastal shelf makes cities along the Gulf of Mexico more vulnerable to storm surges during hurricanes.

Thousands of Florida residents have been forced to evacuate as the state prepares for rapidly strengthening Tropical Storm Helene, which could bring powerful winds, flooding and life-threatening storm surge to areas already hard-hit by recent hurricanes.