By Nicole Chavez and Jason Hanna, CNN

(CNN) -- The devastation left by Hurricane Michael in several states is still coming into focus, with coastal Florida cities destroyed beyond recognition, and homes, businesses and agriculture torn or swamped inland from Georgia to Virginia.

Hundreds of thousands are left without electricity, and emergency officials have no access to many towns. The US death toll has risen to at least 18 -- including five in Virginia and four in Florida -- and it's expected to climb.

"I expect the fatality count to rise today and tomorrow as we get through the debris," Federal Emergency Management Agency Administrator Brock Long said Friday morning.

Michael, which smacked Florida's Panhandle as one of the most powerful hurricanes to hit the United States, left Virginia's coast as a post-tropical low early Friday -- and its trail of destruction will take weeks to take into account.

Aerial footage shows coastal cities in the Panhandle, like Mexico Beach, wiped out. Residents are walking through debris, some assessing the damage and others trying to find food.

Dawn Vickers rode out the storm in Mexico Beach, but her house and vehicles were demolished. Without cell phone service or transportation, she has been taking shelter in one of the few condos left standing, invited by someone she met at what's left of a gas station.

"This has been the worst nightmare I've ever been through in my life," she told CNN on Friday.

A psychiatric hospital in Florida is isolated after downed trees blocked roads around Chattahoochee, and a tree caused a water line to break. The facility is running on power generators, and helicopters have delivered food and water, the state's Department of Children and Families said.

Key developments

• Where is Michael? As of 6:30 a.m. ET Friday, the post-tropical low was moving northeast across the Atlantic Ocean well off Virginia. No tropical cyclone warnings or watches were in effect in the United States. Michael's outer bands still could drop up to 3 inches of rain from New Jersey to Long Island to Cape Cod, and up to 5 inches over the Massachusetts islands of Nantucket and Martha's Vineyard through Friday afternoon, forecasters said.

• In the dark: At least 1.27 million customers in seven states are without power, including 495,000 in North Carolina.

• 13 killed: The dead include five people in Virginia. Four of those drowned, and the fifth was a firefighter who died in a storm-related crash, officials said. Four people in Florida, three people in North Carolina and a child in Georgia also died.

• Severe crop damage: Georgia officials are receiving reports of damage to pecan, cotton, vegetables and peanut crops. "For me the cotton crop is as bad as it gets. I was picking three bale cotton (this week); today it is gone," cotton farmer and state Rep. Clay Pirkle said. "Can't tell the difference between what I've picked and what I haven't."

• Public health emergency declared in Georgia: The move will help ensure those who rely on Medicare and Medicaid have access to the care they need, Health and Human Services Secretary Alex Azar said.

Flooding in the Carolinas and Virginia

The rapid-moving rainfall from Michael triggered flash floods in parts of Virginia and the Carolinas, including areas threatened by swollen rivers during Hurricane Florence.

Hundreds of residents were rescued Thursday from cars, apartments and homes flooded by rushing water.

In Virginia, the Roanoke River jumped its banks and flooded nearby homes and businesses. Cory Patirlo, who lives near the river, said the impact was unexpected. It was the first time he had nearly 2 feet of water in his home.

"It wasn't going to get this high, realistically. It never has," he told CNN affiliate WDBJ.

"I'm gonna be sleeping in my van, with my dogs."

Video that Trina Lockhart posted on Twitter showed drivers making their way cautiously though a flooded Roanoke street Thursday afternoon.

In the southern Virginia city of Danville, floodwaters turned the Grove Park neighborhood into a virtual lake Thursday, and firefighters checked on a nearly submerged car, photos taken by Jim Heffinger show.

The water receded within hours in some areas, and cleanup was underway Friday. Some people are expected to remain in shelters through the weekend as river levels go down.

In North Carolina, Gov. Roy Cooper said first responders rescued nearly 100 people and evacuated many more this week in the face of flash flooding.

Fallen trees have left hundreds of primary and secondary roads closed, he said.

Florida residents return to broken homes

Thousands of residents in the Florida Panhandle are slowly returning to their homes and discovering that everything or almost everything they owned has been reduced to rubble.

Linda Clarke gasped repeatedly at the sight of her once new home in Shell Point Beach -- now severely damaged.

"But you know what ... it's just stuff, it's just stuff," she told her husband, Raoul, as they walked through the ruins. "It's just stuff we can replace."

There is not much left of what used to be the parish hall of St. Dominic Catholic Church in Panama City. Despite the destruction, the Rev. Luke Farabaugh and his congregation celebrated Mass on Thursday.

"Things, we can replace," Farabaugh said on CNN's "Erin Burnett OutFront." "We've seen a lot of signs of hope. ... I've been telling people ... to have hope.

"Hope is that even if the storm does come, even if I lose my car, my house, my family, even if I lose my life, blessed be God," he said. "Our reward isn't just in this life but in the life to come. So we're just trying to give people hope at this point."

In Mexico Beach, Councilwoman Linda Albrecht learned her home was gone through online news video.

"Everything in my house, it was almost like it was pushed back with a bulldozer," she said

"Mexico Beach needs your prayers," Albrecht said of the town of about 1,200 people. "It's not the Mexico Beach we know."

'A freak accident'

Sarah Radney saw trees falling down all around her grandparents' home when Hurricane Michael roared over Georgia. She was safe until a carport came crashing through the roof.

"It was just a freak accident, I never heard of anything like that," said her father, Roy Radney.

Sarah, 11, had just started the sixth grade and joined the drama club and the band. Her father says she loved playing the trumpet, acting and singing.

A man who died when a tree fell on a home near Greensboro, Florida, has been identified as Steven Sweet, according to Lt. Anglie Hightower, Gadsden County sheriff's public information officer.

Three others died in Gadsden County, Hightower said. Authorities did not discuss the circumstances of their deaths, but their bodies have been taken to the medical examiner's office to determine the cause of death.

In North Carolina, a 38-year-old man died when a large tree fell on his vehicle Thursday on US 64 east of Statesville, Iredell County Fire Marshal David Souther said.

Two people also were killed in Marion, North Carolina, when their vehicle struck a tree that had fallen due to high winds, said Adrienne Jones, deputy director for the McDowell County Emergency Medical Services.

Hundreds of people have been rescued from the debris, and authorities fear the toll could climb higher as search-and-rescue efforts continue.

The impact of climate change on storms

Michael's strength may reflect the effect of climate change on storms. The planet has warmed significantly over the past several decades, causing changes in the environment.

Human-caused greenhouse gases in the atmosphere create an energy imbalance, with more than 90% of remaining heat trapped by the gases going into the oceans, according to the National Oceanographic and Atmospheric Administration.

While we might not get more storms in a warmer climate, most studies show storms will get stronger and produce more rain. Storm surge is worse now than it was 100 years ago, thanks to the rise in sea levels.

And unless the rate of greenhouse gas emissions changes, hurricanes are expected to intensify more rapidly in the coming decades, the scientific research group Climate Central said.

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