Paulette McLin takes in the scene Wednesday ahead of Hurricane Helene, expected to make landfall Thursday evening, in Alligator Point, Fla. Gerald Herbert/Associated Press

TALLAHASSEE, Fla. — An enormous Hurricane Helene swamped parts of Mexico on Wednesday as it churned on a path forecasters said would take it to Florida as a potentially catastrophic storm with a surge that could swallow entire homes, a chilling warning that sent residents scrambling for higher ground, closed schools, and led to states of emergency throughout the Southeast.

Helene’s center was about 430 miles southwest of Tampa, Florida, the U.S. National Hurricane Center said, and the hurricane was expected to intensify and accelerate as it crosses the Gulf of Mexico toward the Big Bend area of Florida’s northwestern coast. Landfall was expected sometime Thursday evening, and the hurricane center said by then it could be a major Category 4 storm with winds above 129 mph.

Tropical storm conditions were expected in southern Florida Wednesday night, spreading northward and encompassing the rest of Florida as well as Georgia and South Carolina through Thursday night. The storm was moving north at 12 mph with top sustained winds of 85 mph Wednesday evening.

Helene could create a life-threatening storm surge as high as 20 feet in parts of the Big Bend region, forecasters said. Its tropical storm-force winds extended as far as 345 miles from its center.

The fast-moving storm’s wind and rain also could penetrate far inland: The hurricane center posted hurricane warnings well into Georgia and tropical storm warnings as far north as North Carolina, and it warned that much of the Southeast could experience prolonged power outages, toppled trees and dangerous flooding.

“Just hope and pray that everybody’s safe,” said Connie Dillard, of Tallahassee, as she shopped at a grocery store with thinning shelves of water and bread before hitting the highway out of town. “That’s all you can do.”

One insurance firm, Gallagher Re, is expecting billions of dollars in damage in the U.S. Around 18,000 linemen from out of state staged in Florida, ready to help restore power. Airports in St. Petersburg, Tallahassee and Tampa were planning to close on Thursday, and 62 hospitals, nursing homes and assisted living facilities evacuated their residents Wednesday.

Georgia activated 250 National Guard soldiers for rapid deployment. State game wardens, foresters and Department of Correction teams will help provide swift-water rescues and other emergency responses.

State meteorologist Will Lanxton said tropical storm-force winds are expected throughout Georgia. Lanxton said metro Atlanta hasn’t seen sustained tropical storm winds since Hurricane Irma in 2017.

Visitors to the Southernmost Point marker in Key West, Fla., are hit by wind-driven waves from approaching Hurricane Helene on Wednesday. Rob O’Neal/The Key West Citizen via AP

“I think we’re going to see some significant power outages, probably nothing like we’ve seen, because it’s 159 counties wide,” said James Stallings, director of the Georgia Emergency Management and Homeland Security Agency.

In Tallahassee, where stations started to run out of gas, 19-year-old Florida A&M student Kameron Benjamin filled sandbags with his roommate to protect their apartment before evacuating. Their school and Florida State shut down.

“This hurricane is heading straight to Tallahassee, so I really don’t know what to expect,” Benjamin said.

As Big Bend residents battened down their homes, many saw the ghost of 2018’s Hurricane Michael. That storm rapidly intensified and crashed ashore as a Category 5 that laid waste to Panama City and parts of the rural Panhandle. On Wednesday, the National Weather Service posted an urgent warning for residents along Apalachee Bay:

“There is a danger of catastrophic and unsurvivable storm surge for Apalachee Bay,” it said. “Storm surge may begin to arrive as early as late Wednesday night ahead of the winds. This forecast, if realized, is a nightmare surge scenario for Apalachee Bay. Please, please, please take any evacuation orders seriously!”

“People are taking heed and hightailing it out of there for higher ground,” said Kristin Korinko, a Tallahassee resident who serves as the commodore of the Shell Point Sailboard Club, on the Gulf Coast about 30 miles south of Tallahassee.

For toughened Floridians who are used to hurricanes, Robbie Berg, a national warning coordinator for the hurricane center, advised: “Please do not compare it to other storms you may have experienced over the past year or two.”

Helene is forecast to be one of the largest storms in breadth in years to hit the region, said Colorado State University hurricane researcher Phil Klotzbach. He said since 1988, only three Gulf hurricanes were bigger than Helene’s predicted size: 2017’s Irma, 2005’s Wilma and 1995’s Opal.

Areas 100 miles north of the Georgia-Florida line can expect hurricane conditions. More than half of Georgia’s public school districts and several universities canceled classes.

And for Atlanta, which is under a tropical storm watch, Helene could be the worst strike on a major Southern inland city in 35 years, said University of Georgia meteorology professor Marshall Shepherd.

“It’s going to be a lot like Hugo in Charlotte,” Shepherd said of the 1989 storm that struck the North Carolina city, knocking out power to 85% of customers as winds gusted above hurricane force.

Landslides were possible in southern Appalachia, with catastrophic flooding predicted in the Carolinas and Georgia, where all three governors declared emergencies. Rainfall is possible as far away as Tennessee, Kentucky and Indiana.

Parts of Mexico’s Yucatan Peninsula were under hurricane warnings as Helene wound between it and the western tip of Cuba and into the Gulf of Mexico. The storm formed Tuesday in the Caribbean, and it flooded streets and toppled trees as it passed offshore and brushed the resort city of Cancun.

In Cuba, authorities moved cattle to higher ground and medical brigades went to communities often cut off by storms. The government preventively shut off power in some communities as waves as high as 16 feet slammed Cortes Bay. In the Cayman Islands, schools remained closed as residents pumped water from flooded homes.

In the U.S., federal authorities positioned generators, food and water, along with search-and-rescue and power restoration teams.

Florida Gov. Ron DeSantis warned that Helene could be as strong as a Category 4 hurricane when it makes landfall. The state was providing buses to evacuate people in the Big Bend region and taking them to shelters in Tallahassee.

But near Florida’s center, outside Orlando, Walt Disney World said its only closures Thursday would be the Typhoon Lagoon water park and its miniature golf courses.

Helene is the eighth named storm of the Atlantic hurricane season, which began June 1. The National Oceanic and Atmospheric Administration has predicted an above-average Atlantic hurricane season this year because of record warm ocean temperatures.

In the Pacific, former Hurricane John reformed Wednesday as a tropical storm and was strengthening as it threatened areas of Mexico’s western coast. Officials posted hurricane warnings for southwestern Mexico.

John hit the country’s southern Pacific coast late Monday, killing at least two people, triggering mudslides, and damaging homes and trees. It grew into a Category 3 hurricane in a matter of hours and made landfall east of Acapulco. It reemerged over the ocean after weakening inland.

Associated Press journalists Seth Borenstein in New York; Jeff Amy in Atlanta; Danica Coto in San Juan, Puerto Rico; Andrea Rodríguez in Havana; Mark Stevenson and María Verza in Mexico City; and Claire Rush in Portland, Oregon, contributed to this report. Hollingsworth reported from Mission, Kansas.