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.
Hurricane Helene winds increase to 140 mph
Hurricane Helene has grown stronger as it nears landfall, with sustained winds of 140 mph.
As of 9 p.m. ET, the hurricane was 65 miles west of Cedar Key, Florida, and 90 miles south of Tallahassee.
The hurricane is moving at 24 mph and is still on track to make landfall between 10 p.m. and 11 p.m. ET.
Extreme wind warning issued for Tallahassee area
The National Weather Service issued an extreme wind warning for three cities in the Tallahassee area on Thursday night.
The warning is in effect until midnight in Perry, Madison and Monticello.
"Treat these imminent extreme winds as if a tornado was approaching and move immediately to an interior room or shelter NOW!" the agency said.
Hurricane Helene in photos
As Florida is bracing for Hurricane Helene to make landfall, heavy rain and winds are battering Florida's Gulf Coast.
More than 500,000 customers without power in Florida
Over 500,000 customers have lost power across Florida in the run up to Hurricane Helene making landfall.
As of 9 p.m. ET, 545,587 customers did not have power usage, according to poweroutage.us.
Helene is expected to make landfall between 10 p.m. and 11 p.m. ET in Florida's northeast Gulf Coast region.
Latest forecast
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