Hurricane Idalia is intensifying and is expected to make landfall in Florida at Category 4 strength, bringing “extremely dangerous” conditions, US forecasters have warned.

The National Hurricane Centre says Idalia’s centre is forecast to reach the Big Bend coast on Wednesday morning local time and it 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 later in the day.

Florida Governor Ron DeSantis has declared a state of emergency for 46 counties ahead of the arrival of the hurricane.

The National Hurricane Centre has warned of catastrophic impacts from storm surge inundations of 12-16 feet above ground and says there is the potential for destructive life-threatening winds.

“Idalia is expected to produce a swath of 4 to 8 inches of rainfall with isolated maxima up to 12 inches from the Florida Big Bend through central Georgia and South Carolina, and through eastern North Carolina into Thursday,” it says. “These rainfall amounts will lead to areas of flash, urban, and moderate river flooding, with locally considerable impacts.”

The hurricane is set to reach Florida less than a year after Hurricane Ian caused extensive damage after crossing the state’s coastline in late September. Ian became the costliest hurricane in Florida’s history and the third-costliest in US history.

The Atlantic hurricane season runs from June 1 to November 30.