Helene is forecast to make landfall in Florida on Thursday night.
Helene -- which has strengthened to a major Category 4 hurricane -- is taking aim at Florida, where it's forecast to make landfall along the Big Bend area on Thursday night.
Airlines have canceled more than 1,200 flights across the country as Hurricane Helene moves in.
The airports seeing the biggest impacts are Hartsfield-Jackson Atlanta International Airport, Southwest Florida International Airport in Fort Myers and Tampa International Airport.
Tampa International Airport, Tallahassee International Airport and St. Pete-Clearwater International Airport are all closed on Thursday.
Hurricane Helene is forecast to make landfall as a major hurricane between 9:30 p.m. and 11:30 pm. Thursday in Florida's Big Bend region.
Because Helene is a very large hurricane, it will impact nearly all of Florida.
Helene is set to bring catastrophic storm surge up to 20 feet to the Big Bend area. Four to 8 feet of storm surge is expected around Tampa Bay.
The major 110 mph winds will cause widespread tree damage and power outages across the Florida Panhandle and the Big Bend area.
Tornado watches are in effect for most of Florida and parts of Georgia and South Carolina through Thursday night.
By Friday morning, Helene will weaken to a tropical storm as it moves north through Atlanta with heavy rain and strong winds.
Georgia should be prepared for hurricane-force wind gusts to cause damage and power outages.
Rainfall totals from Helene will be 6 to 12 inches, with locally up to 20 inches in some areas.
Catastrophic and life-threatening flash flooding, as well as significant landslides, are expected across portions of the southern Appalachians through Friday. There is an extreme flood risk from Tallahassee, Florida, to Atlanta to Asheville, North Carolina.
-ABC News' Melissa Griffin
All counties in Georgia are under a state of emergency as Hurricane Helene nears.
"This is a big storm -- it’s going to affect the entire state," Georgia Gov. Brian Kemp said.
"This storm is one of the biggest we’ve ever seen in the Atlantic in terms of size, covering nearly 500 miles," he said.
Kemp cautioned about the potential for flash flooding and tornadoes, particularly in areas on the "dirty side" of the storm
"This storm will bring strong winds and a lot of rain. Flooding and even landslides in mountainous areas are a real possibility," he said.
-ABC News’ Jason Volack
Helene strengthened to a major Category 3 hurricane with 120 mph winds on Thursday afternoon.
Helene could strengthen even more before it makes landfall Thursday night.
