Hurricane Isaias strengthened to Category 3 on Friday morning as it approached the US Gulf coast. States of emergency have been declared in Alabama, Florida and Mississippi ahead of its forecast landfall near the Alabama-Florida border on Friday night.

Officials warned of a potentially life-threatening storm surge. The National Hurricane Center said Dauphin Island, off Alabama, could see a surge of up to 7ft (2.1 metres), while up to 6ft (1.8 metres) was possible at Indian Pass on the Florida coast. Waves could reach 30ft (9.1 metres).

A hurricane warning covers parts of the Florida panhandle, southern Alabama and southern Mississippi. The National Oceanic and Atmospheric Administration urged residents there to prepare for prolonged power cuts; it also forecast storm surge from south-east Louisiana to north-east Florida.

Coastal areas could receive up to 15in (380mm) of rain, and tornadoes are possible overnight into Saturday. Heavy rain had already begun along the coast on Friday morning. Isaias is expected to weaken quickly after landfall.