The National Hurricane Center warned there is a danger of life-threatening storm surges along Florida’s Gulf Coast with 1.8 to 3m of inundation above ground level in some areas.

The storm will probably cause catastrophic flooding with “potentially historic heavy rainfall” when Debby moves northeast across Georgia and South Carolina over the next few days, the NHC said.

“We are looking at potentially really, really significant flooding that will happen, particularly in north-central Florida,” governor Ron DeSantis told an emergency briefing on the storm on Sunday.

He and NHC deputy director Jamie Rhome have stressed that Floridians should be making and completing their final emergency preparations immediately.

As of 11pm local time yesterday, Debby was about 160km west of Tampa carrying maximum sustained winds of 120kph and moving north at 19kph, the advisory said.

As residents rushed to prepare, mandatory evacuations were ordered for part of Citrus County, Florida, with eight other counties under voluntary evacuation orders, local media reported.

“Take the situation seriously,” Paul Hasenmeier, Hernando County fire chief and public safety director, told reporters late Saturday. “We know the water’s going to come up as the storm passes.”

Debby is expected to dump 15 to 31cm of rain in parts of Florida, and as much as 51 to 76cm in coastal Georgia and South Carolina before the week is over, the NHC said.

The governors of Georgia and South Carolina have declared a state of emergency ahead of the storm’s arrival.

Brennan predicted “multiple days of very, very heavy rainfall” — at possibly record-breaking levels. He said there likely will be severe flash flooding “in areas that don’t normally flood.”

President Joe Biden on Sunday approved an emergency declaration for Florida, allowing federal aid to be expedited.

DeSantis has activated the state’s National Guard, with 3,000 service members on standby to help with storm response.