GREENVILLE, N.C. — Hurricane Florence began its brutish slow-motion collision with the Carolina coasts Thursday, with beach towns cowering under the first bands of lashing rain and storm surge. Onshore wind gusts reached 100 miles per hour.

At the same time, residents and emergency personnel throughout inland North and South Carolina were working under the grim assumption that the Category 1 storm’s pounding of the coastline would be only the first powerful punch in a fight that could go many rounds and last for many days. It will play out not only among stilted beach cottages and seaside resorts, but also in workaday towns and cities much farther west.

“This may be the first time we’ve experienced such a two-punch from these kind of conditions,” said South Carolina’s governor, Henry McMaster, at a news conference on Thursday, speaking about evacuations along the coast as well as the possibility of rain-triggered landslides in the mountains.

Florence is proving to be a lumbering giant, with cloud cover as large as the Carolinas themselves. If, as expected, it dawdles over the region, the storm could drop rainfall of 20, 30 or even 40 inches in some areas. Anxiety is especially high over the fate of all of that water, which will have to go somewhere.

That means a cascading series of complications for a city like Greenville, N.C., a handsome college town of 92,000 people set on the banks of the Tar River.

The city lies far inland, a few score miles west of the Atlantic Ocean, but it is connected to the sea by the Tar River, which eventually becomes the Pamlico River as it widens out and flows into the Atlantic.

On Thursday, as billowing, dark heather clouds loomed overhead, the city’s spokesman, Brock Letchworth, said Greenville’s first concern is that Florence could drop enough water to create immediate flash flooding.

But he said the city was also worried about a massive salty storm surge roaring westward up the river from the Atlantic. Finally, there is the problem of all the rainfall on the rest of the state, which would have to eventually drain eastward out toward the ocean.

City and county officials have stationed swift-water rescue groups in place, including teams of wildlife officers from Indiana. Police have begun going door to door in the lowest-lying areas suggesting that residents get out. Some 300 people were already using five Pitt County shelters.