The US National Hurricane Center says parts of Alabama and the Florida panhandle could see historic flooding when hurricane Sally makes landfall near the Alabama-Mississippi state line sometime today or early tomorrow.
The Category 1 storm is crawling toward the northern Gulf Coast at just three kilometres per hour.
Forecasters say some places could be inundated with almost two metres of water.
Alabama Gov. Kay Ivey is urging residents near Mobile Bay and low-lying areas near rivers to evacuate if conditions still permit a safe escape from Hurricane Sally.