“Idalia is a category 3 hurricane on the Saffir-Simpson Hurricane Scale. Additional strengthening is forecast, and Idalia is forecast to become a category 4 hurricane before it reaches the Big Bend coast of Florida this morning,” the weather agency reported in an advisory issued at 2am local time.

“Hurricane Hunter aircraft data indicate that maximum sustained winds have increased to near 195kph with higher gusts,” it added.

“Idalia is likely to still be a hurricane while moving across southern Georgia, and possibly when it reaches the coast of Georgia or southern South Carolina late today.”

Authorities in Florida had earlier described Idalia and its potentially deadly storm surge as a once-in-a-lifetime event for the state’s northwest coast, ordering mass evacuations and issuing flood alerts ahead of its projected landfall.

Warm waters in the Gulf of Mexico are expected to further turbocharge Idalia, with wind speeds of 209-251kph forecast, the NHC said.

It warned of potentially disastrous storm surge inundation of 3-5m in some coastal areas.