The immense task of preparing for Hurricane Helene, a storm so large that no part of Florida may be untouched by wind, rain or storm surge, fell disproportionately on Wednesday to the frustrated people of the Gulf Coast, whose memories of recent storms remain vivid.

They are people like Amy Bormann, a waitress who lives on a 30-foot sailboat in St. Marks, a tiny city on the northern Florida coast south of Tallahassee. During Hurricane Michael in 2018, she recalled, the storm surge rose higher than her head was.

“We’re tough down here,” said Ms. Bormann, 45, who also lived through Hurricane Katrina in New Orleans in 2005.

But on Wednesday, as she helped pack grills and food into a trailer from the Cooter Stew, the burger joint where she works across the street from the Wakulla River, she worried aloud that Helene, which is expected to make landfall late on Thursday, appeared to be heading directly toward St. Marks.

“It looks bad,” she said.

All of Wakulla County, which includes St. Marks, was under mandatory evacuation orders on Wednesday, as were several other coastal counties along the Big Bend region, the area where the peninsula and the Panhandle of Florida meet.

The worst of Helene’s storm surge — up to 18 feet — is expected along the marshy and sparsely populated Big Bend. Helene would be the third named storm to strike the region in 13 months, after Hurricane Idalia in August of last year and Hurricane Debby last month.