Hurricane Debby makes landfall on Florida's Gulf Coast

Hurricane Debby made landfall as a Category 1 storm in the Big Bend region of Florida's Gulf Coast on Monday morning and began a slow crawl across the state, causing potentially dangerous storm surges, heavy rainfall and catastrophic flooding.

The hurricane came ashore near Steinhatchee, Florida, about 115km southeast of Tallahassee, packing maximum sustained winds of 130kmph, the National Hurricane Centre said.

The system grew from a slow moving tropical storm that gained strength from warm Gulf waters. The hurricane centre forecast life-threatening conditions, including storm surges up to three metres in some areas.

The storm could bring "potentially historic rainfall" of between 25 and 50cm and catastrophic flooding to Georgia and South Carolina, the NHC said. Local areas could receive 70.2cm of rain by Friday morning.

"This is going to be the story of this storm," said Jamie Rhome, the deputy director of the hurricane center. "It's slow motion is going to dump historic amounts of rainfall — potentially over 50cm. You're talking about catastrophic flooding."

Rhome said Debby was fuelled by exceptionally warm Gulf waters.

It bears some of the hallmarks of Hurricane Harvey, which hit Corpus Christi, Texas, in August 2017. While downgraded into a tropical storm as it moved inland, Harvey lingered over the state, dumping about 127 inches of rain on Houston.

Harvey is rated as one of the wettest storms in US history, causing more than 100 deaths and $125 billion in damage, primarily from flooding in the Houston metropolitan area.

Climate scientists believe man-made global warming from burning fossil fuels has raised the temperature of the oceans, making storms bigger and more devastating.

Some 143,000 Floridians were without power, Florida Governor Ron DeSantis said at a news conference soon after the storm made landfall.

Preparing for Debby, DeSantis called up 3,000 National Guard troops and placed most of the state's cities and counties under emergency orders, while mandatory evacuations were ordered in parts of the Gulf Coast counties of Citrus, Dixie, Franklin, Levy and Wakulla.

DeSantis said on Sunday there were more than 17,000 linemen and other electric workers ready to restore power.

Only one hurricane, Beryl, has yet formed in the Atlantic this year. The earliest Category 5 storm on record, it struck the Caribbean and Mexico's Yucatan peninsula before rolling up the Gulf Coast of Texas as a Category 1 storm, with sustained winds up to 152kmph.