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With millions of coastal residents either on the move or hunkering down anxiously in place, Hurricane Florence surged toward North Carolina on Tuesday, tracing an unusual path that could lead to tremendous destruction — especially if the immense storm dumps enormous amounts of rain as it moves inland.

"This could be an unprecedented disaster for North Carolina," said Brian McNoldy, a senior research associate at the University of Miami, in a post Tuesday on his popular hurricane blog.

A powerful Category 4 storm, Florence should reach land by Friday, and when it does, it is expected to be a monster. In addition to its powerful winds, the storm will slam the low-lying coasts of North Carolina, South Carolina and Virginia with a huge, life-threatening storm surge, the National Hurricane Center has predicted. And once it is ashore, its drenching rains may cause "catastrophic flash flooding and significant river flooding" over a wide area of the Carolinas and the mid-Atlantic states.

Many coastal residents and vacationing tourists streamed inland Tuesday, prompted by evacuation orders issued by the governors of North and South Carolina and many local authorities.

Others said they would wait, hoping to squeeze in one more day of fishing or beachgoing before heading for the hills. And some said they would defy the storm and stay put.

In Nags Head, N.C., a small beach town in the vulnerable Outer Banks, Mayor Ben Cahoon said he and his wife had decided not to go, despite a mandatory evacuation order that he had helped develop.

"There are folks like myself, who have lived here a long time, who sort of have a sense about these things," he said. "Whether that's entirely rational or not, that's ­something else."

Cahoon, 56, said he would stay for both personal and professional reasons: He wants to be in his own home during the storm, and to be on hand in town in the immediate aftermath to help his constituents recover.

Florence promises to dump exceptional amounts of rain, both on the coast and farther inland.

The National Hurricane Center said 15 to 20 inches could fall in many areas, with some localities getting as much as 30 inches. Intense rainfall from tropical storms holds a special threat for areas with hilly or mountainous terrain: In 2011, Hurricane Irene washed out a dozen bridges and 500 miles of roads in Vermont alone.

State officials said it was too soon to gauge the success of their mass evacuation orders. In Carolina Beach, N.C.,an island community south of Wilmington, about 75 percent of residents had left by Tuesday afternoon, according to town manager Michael Cramer. He said some of the rest would leave on Wednesday, but there were die-hards who would try to ride out the storm in town.

"If somebody needs help, they may be out of luck," ­Cramer said.

Several major highways in South Carolina were made one-way only Tuesday to accommodate people fleeing the coast. Traffic on U.S. 501, which runs north from Myrtle Beach, was four to six times heavier than normal on Tuesday, according to Capt. Kelley Hughes of the state Highway Patrol, while Interstate 26, running west from Charleston, had triple the normal volume.

Across the region, government offices and school systems closed Tuesday or said they would do so Wednesday or Thursday, with some school buildings earmarked for duty as emergency shelters. Giant manufacturers like Boeing, Mercedes-Benz and Volvo that have plants in the region suspended operations, and Walmart closed dozens of stores.

Cellphone carriers including AT&T and Verizon said they were fueling and testing generators in the hope of maintaining service if the storm knocks out electric power, as it is likely to do in many areas.

Utilities warned that restoring power after the storm could take days or even weeks. Duke Energy said it was moving crews to the Carolinas from its divisions in Indiana, Ohio, Kentucky and Florida, and would borrow crews from other utilities outside the storm area.

The South Carolina Electric and Gas Co. said it would release water through its hydroelectric dam on Lake Murray before the storm to lower the water level in the reservoir and head off ­flooding.

Climate change is probably contributing to the menace posed by storms like Florence. Gabriel Vecchi, a Princeton climate scientist, noted that while many scientists are wary of drawing firm links between any particular storm and climate change, a rising sea level adds to the destructiveness of storm surges, and a warming atmosphere holds more moisture, leading to more rain.

A study in December estimated that Hurricane Harvey's rainfall total last year was 38 percent higher than it would have been in a world without climate change.

The storm's rising strength may also be influenced by climate change, according to Jennifer Francis, a Rutgers research professor. She noted that warm ocean water, a source of power for such storms, is currently plentiful in the Atlantic.

And the potential for Florence to linger over the Carolinas after it makes landfall, as Harvey did over the Houston area last year, could also be linked to climate change, Francis said.