Michael killed at least six people - including a man who died when a tree toppled onto his house in Florida and a girl who died when debris fell into a home in Georgia, officials and local media said.
"You could tell they were flummoxed", Phil Klotzbach, research scientist in the Department of Atmospheric Science at Colorado State University, said Thursday.
Spots in Morganton and Mocksville saw more than 5 inches of rain, says the USGS.
States of emergency have been declared in all or parts of Florida, Alabama, Georgia and North Carolina.
Many people who evacuated the Florida Panhandle now have nowhere to work or live. Before and after images reveal formerly lush green neighborhoods in the small community that have been completely wiped out - with most homes and businesses completely flattened or heavily damaged.
Nearly 1.1 million homes and businesses were without power from Florida to Virginia early on Friday, according to utility companies.
The hurricane tore through Florida with powerful winds, uprooting trees, shredding roofs and turning over cars.
Hurricane Michael left "unimaginable destruction" as it ploughed into coastal areas of Florida, the state's governor, Rick Scott says.
Much of downtown Port St. Joe, 12 miles (19 km) east of Mexico Beach, was flooded. "It was the most attractive, secret location you could have for a vacation".
Video shot by CNN from a helicopter showed homes closest to the water in Mexico Beach had lost all but their foundations. In August 2004, Hurricane Charley strengthened from 110 mph to 150 mph in just a few hours before striking Florida's Gulf coast south of Sarasota.
"This is a war zone".
"It wasn't going to get this high, realistically". Hanson asked. "This city is destroyed". "It went through Florida very, very quickly, it didn't linger, it didn't come back, as we had in Texas". A nearby resident, Cory Patirlo, said he had almost 2 feet of water in his home. But the fate of many residents was unknown.
At the National Hurricane Center, as the storm's growing power was becoming clear, one forecaster wrote that its rapid intensification in the face of unfavorable high-altitude winds "defies traditional logic". "We thought the windows were going to break at any time", Beu said.
The intense power of Michael caught many people off guard.
The death toll from Hurricane Michael rose to at least 13 on Friday - including one first responder - and is expected to increase further as crews search for survivors in the devastating storm's aftermath.
Ahead of Michael among USA hurricanes were the 1935 Labor Day hurricane, which left 485 dead; Hurricane Camille, which killed 259 people in 1969, and Hurricane Andrew in 1992, which resulted in 65 deaths, and. "All major roadways are passable", the city said, adding that 83 percent of its traffic signals were operating normally.
"Hurricane Michael can not break Florida", Scott vowed. "I have seen cotton that was being harvested yesterday".
"I was sinkin', sinkin' fast.when I turned I immediately started sinkin' and I knew that I had hit the ditch and I put it in reverse and of course, it didnt go anywhere".
Tropical storm condition will continue to batter parts of the United States southeast coast from Georgia through to North Carolina. Three other firefighters were seriously injured in the crash.
As of this morning, Michael is a post-tropical storm off the Eastern Seaboard.