More than 12 million people, from Florida and Georgia to Alabama and South Carolina, are in a high-risk area where heavy rainfall is expected to cause disruption and flooding.

“Catastrophic and life-threatening flash flooding from Helene is likely for portions of the southeastern and southern Appalachians,” the National Weather Service said.

“Most flood fatalities occur in vehicles, turn around and don’t drown!”

The areas at greatest risk include parts of North Carolina, Tennessee, Georgia and the Florida Panhandle.

Major cities like Asheville, Charlotte and Greenville are at risk of receiving 6 to 12 inches of rain, while isolated areas may see as much as 20 inches.

Hurricane Helene is considered one of the worst storms to hit the US.

Helene’s size is enormous compared to previous hurricanes in the Gulf of Mexico. Officials warned of “catastrophic” and “unsurvivable” conditions ahead of the storm’s arrival.

The storm made landfall as a Category 4 hurricane and is expected to continue producing hurricane-force winds as it moves inland.

Helene quickly evolved from a category one storm to a catastrophic category four hurricane, something that has happened regularly in recent years as ocean temperatures remain higher than normal.

“Helene moves over very warm water of at least 80 degrees and reaches depths of 90 to 120 meters below the surface. That heat energy will help Helene explode in intensity this afternoon and tonight,” Alex DaSilva, AccuWeather’s lead hurricane expert, said Thursday before landfall.

Storms now are 25 percent more likely than 40 years ago to be classified as major hurricanes because hot water fuels the storms.

Hurricane Helene is now moving north into Georgia after making landfall in Florida, forecasters say.

The eyewall – the part of the storm with the fastest winds underneath – is now pushing into southern Georgia, the National Hurricane Center said in its 1am ET (6am BST) update.

The storm had begun to weaken somewhat, the NHC said in its update, but it was expected to remain a hurricane.

“Please do not leave your shelter and remain in place during these life-threatening conditions,” the update said.

It said Helene “continues to produce catastrophic winds.”

Helene is expected to remain a full-fledged hurricane as it barrels through the Macon, Georgia, area on Friday, forecasters said.

It could bring 12 inches of rain or more, potentially devastating the state’s cotton and pecan crops, which are in the middle of harvest season.

“The current forecast for Hurricane Helene suggests this storm will impact every part of our state,” Georgia Governor Brian Kemp said.

After making landfall along the Florida coast, Helene is expected to move more slowly over the Tennessee Valley on Friday and Saturday, the NHC said.

Here is the path of the storm:

At least one person has died in Florida after the Category 4 storm made landfall, causing severe flooding.

The identity of the person and the cause have not been shared, but Gov. Ron DeSantis said at a news conference that it happened on Interstate 4 near Tampa.

He urged people not to travel, saying the “roads can be dangerous” and it is “very, very dangerous”.

DeSantis warned that there will likely be “additional” fatalities in the state as the storm moves through.

“When Floridians wake up tomorrow morning, we will wake up to a state where more lives have most likely been lost,” he said. “And there will certainly be property loss.”

He notes that emergency services do not yet know the extent of the impact because it is nighttime in Florida.

“We don’t get the full picture yet,” he says.

The Florida Highway Patrol in Tampa said Thursday afternoon it would close the Sunshine Skyway Bridge as conditions in the area continue to change.

“As weather conditions continue to deteriorate and wind gusts have reached 60 MPH, FHP is closing the #Skyway,” the patrol wrote on X.

“Motorists are urged to seek alternative routes, avoid driving on flooded roads and stay off area roads unless absolutely necessary.”

The southern Appalachians are expected to experience strong, damaging winds and rainfall up to a foot, with some isolated amounts of eight inches.

“These rainfall events are likely to result in catastrophic and potentially life-threatening flooding and urban flooding, together with significant river flooding. Numerous large landslides are expected in steep terrain in the southern Appalachians,” the National Hurricane Center warned.

The National Weather Service’s Greenville-Spartanburg, South Carolina office warned of “one of the most significant weather events to occur across the western portions of the region in modern times.”

“Record flooding is forecast and compared to the 1916 floods in the Asheville area,” the report said.

Category 4 Hurricane Helene made landfall in Florida’s Big Bend region on Thursday evening, packing deadly winds of 140 mph (230 km/h) and a “catastrophic” storm surge.

Poweroutage.us now reports that more than a million people are without power.