Florida residents prepared for a heavy blow from Hurricane Helene as the Category 4 storm churned northward Thursday, prompting warnings of pounding rain and a storm surge that could create “unsurvivable conditions” in some areas.

Helene strengthened into a Category 4 hurricane hours ahead of its expected landfall on Florida’s northwest coast Thursday night, and forecasters warned that the enormous storm could create a “nightmare” surge in coastal areas and bring dangerous winds and rain across much of the southeastern U.

Hurricane Helene, a massive, destructive Category 4 hurricane causing catastrophic storm surge, made landfall about 11:10 p.m. Thursday in Florida’s Big Bend, the National Hurricane Center