(CNN) Editor's note: This is a developing story that is being constantly updated as the storm progresses.

Leaving a trail of devastation in Florida, Irma trudged north on Monday, flooding downtown Charleston, South Carolina, uprooting trees in Atlanta and cutting off coastal communities.

A weakened Irma -- downgraded to a tropical depression Monday night -- still packed power. At least three storm-related deaths were reported in Georgia and one in South Carolina. The deaths occurred mostly when tree limbs fell on victims during the tropical storm that stretched 650 miles from east to west, affecting at least nine states.

As Jacksonville, Florida, grappled with record storm surge, the level of the destruction became more apparent in the hard-hit Florida Keys at the southern tip of the state. Areas without water, power or communications are likely to remain so for some time.

Irma flooded portions of River Street in the tourist magnet city of Savannah, Georgia and forced police to temporarily shut Highway 80 leading to the barrier island community of Tybee Island. Water also filled The Battery, the downtown Charleston neighborhood where the Ashley and Cooper rivers meet. Charleston police asked residents to avoid downtown in anticipation of high tide.

Charleston Police is asking citizens to avoid downtown Charleston until flooding subsides and conditions improve. #chsnews #chswx #chstrfc — Charleston P.D. (@CharlestonPD) September 11, 2017

Waters in Charleston Harbor peaked at nearly 10 feet high, the city's third-highest reading, topping Hurricane Matthew in 2016, said CNN meteorologist Taylor Ward.

High tide today at the Battery. #hurricaneirma A post shared by David Blackmon (@_dblackmon88_) on Sep 11, 2017 at 10:42am PDT

Parts of coastal Georgia and South Carolina remained under storm surge warning late Monday.

Irma will continue to weaken, but the rain and wind will spread further north. The storm was moving towards Alabama late Monday. It is forecast to move to Tennessee on Tuesday before fizzling out later this week, forecasters said.

The latest developments:

-- As of Monday night, Irma was centered about 95 miles south of Atlanta, with maximum sustained winds of 35 mph, the National Hurricane Center said.

-- A 57-year-old South Carolina man was fatally injured by a falling tree limb during the storm, Abbeville County Coroner Ronnie Ashley told CNN. The man was cutting downed limbs with a chainsaw outside of his home when he was struck.

-Three people died in Georgia: A 62-year-old man who was on his roof was killed in Worth County, which experienced wind gusts of 69 mph, according to Kannetha Clem, a spokeswoman for the Worth County Sheriff's Office. Another man was killed in Sandy Springs, an Atlanta suburb, when a tree fell and "literally cut the home in half,"said Sharon Kraun, the city's communications director. One woman was killed when a downed tree struck her vehicle in Cumming as the car at in a private driveway, the Forsyth County Sheriff's Office.

-- About 6.2 million electric customers were without power in Florida late Monday, according to Floridadisaster.org . FEMA chief Brock Long has said some places won't have electricity for weeks.

-- More than 1.4 million customers in Georgia were without power, according to Georgia Power and Georgia EMC

-- In South Carolina, nearly 200,000 customers were without power, according to utility companies.

'We're definitely shaken up'.

Irma turned Jacksonville's Memorial Park into an unrecognizable lake.

Hurricane Irma #irma #hurricaneirma #storm #memorialpark #riverside #river @news4jax A post shared by AnaMaria (@italian_crafter) on Sep 11, 2017 at 9:18am PDT

"We have very serious, significant river flooding along the banks of the St. Johns River. It's bad now, it's going to continue to get worse," meteorologist Angie Enyedi said. "We've already surpassed historic levels, the levels will continue to rise."

In one Jacksonville yard, Irma snapped a tree near its roots, sending it crashing onto the car of an evacuee from South Florida on Sunday.

No one was hurt. The tree at the end of Kristine Garcia's driveway, luckily, didn't fall on her house.

"We're definitely shaken up. We were in shock when we went outside," Garcia, 34, told CNN Monday. "If it would have fallen toward our direction, it would have been a ... mess."

No electricity or safe water

Irma devastated much of Marco Island, off the southwest coast of Florida, leaving it with no electricity or clean water.

Roommates Zack Forrest and Krock Indigo rode out the storm on the island and likened Irma to a relentless tornado. "The storm was really intense, it was like a tornado that lasted for an hour and a half," Forrest said.

"No way!" Indigo interrupted. "It was like 5 hours."

By the time Irma finished with Marco Island, it left 15 homes that have either lost their roofs or suffered other severe damage, the fire department said.

The good news is that there were no major injuries, said Marco Island Fire Chief Mike Murphy

"We were the little engine that did it," he told CNN's Ed Lavandera.

Tara O'Neill arrived at her house in Goodland, Florida, on Monday for the first time since the eye of the storm hit the small fishing village at the southeast corner of Marco Island. A tree had crushed her home.

"It's never good when you show up and see this in front of your house," she quipped.

The Goodland native bought the home in 1998 when it was a "dump," she said . She and her husband spent six years remodeling.

O'Neil climbed on the hood of her car to get a better look and found humor in her devastation.

Looters, she joked, could help themselves to anything they wanted.

In Goodland, Florida, Tara O'Neill returns home to find a large tree crushed her home. The eye of #HurricaneIrma m... https://t.co/0xpWTQYm0n pic.twitter.com/vVAYtZl1fS — ed lavandera (@edlavaCNN) September 11, 2017

Some Florida Keys residents could soon be home

Irma made landfall on the Florida Keys as a Category 4 hurricane Sunday, but the full extent of the damage there is still unknown.

Photos: Hurricane Irma slams Florida Photos: Hurricane Irma slams Florida Children clean a dirty mattress from a flooded home in Immokalee, Florida, on Thursday, September 14. Hurricane Irma laid waste to beautiful Caribbean islands and caused historic destruction across Florida. The cleanup will take weeks; recovery will take months. Hide Caption 1 of 58 Photos: Hurricane Irma slams Florida On September 14, President Donald Trump, Vice President Mike Pence and first lady Melania Trump hand out food to people impacted by Hurricane Irma in Naples, Florida. Hide Caption 2 of 58 Photos: Hurricane Irma slams Florida Debris litters the area around a group of homes in the Florida Keys on Wednesday, September 13. Hide Caption 3 of 58 Photos: Hurricane Irma slams Florida Lake County jail inmates fill sandbags in Astor, Florida, on September 13. Hide Caption 4 of 58 Photos: Hurricane Irma slams Florida A classic Volkswagen sits in floodwaters September 13 in Middleburg, Florida. Flooding from the Black Creek topped the previous high-water mark by about 7 feet. Hide Caption 5 of 58 Photos: Hurricane Irma slams Florida James Wade checks for water-damaged items as floodwaters recede in Middleburg on September 13. Hide Caption 6 of 58 Photos: Hurricane Irma slams Florida Floodwaters surround vehicles in Callahan, Florida, on Tuesday, September 12. Hide Caption 7 of 58 Photos: Hurricane Irma slams Florida Jose Encarnacion pulls a chicken from a cage as he gathers belongings from his flooded house in Bonita Springs, Florida, on September 12. Hide Caption 8 of 58 Photos: Hurricane Irma slams Florida Joseph Dupuis III stacks boxes off the floor in his parents' water-logged apartment in Jacksonville, Florida, on September 12. Hide Caption 9 of 58 Photos: Hurricane Irma slams Florida Motorists in Estero, Florida, fill gas cans September 12, moments before police shut the station down because of a curfew. Hide Caption 10 of 58 Photos: Hurricane Irma slams Florida Mike Gilbert and his daughter Brooke embrace in front of a relative's destroyed condominium building in the Florida Keys on September 12. Hide Caption 11 of 58 Photos: Hurricane Irma slams Florida Members of the US Coast Guard operate in floodwaters during rescue missions in Hastings, Florida, on September 12. Hide Caption 12 of 58 Photos: Hurricane Irma slams Florida Waist-deep in floodwater, Shelly Hughes gets her first look at the inside of her camper in Arcadia, Florida, on September 12. Hide Caption 13 of 58 Photos: Hurricane Irma slams Florida In the aftermath of Hurricane Irma, a house slides into the Atlantic Ocean in Ponte Vedra Beach, Florida, on Monday, September 11. Hide Caption 14 of 58 Photos: Hurricane Irma slams Florida Richard Shieldhouse maneuvers through storm-surge floodwaters in Jacksonville on September 11. Hide Caption 15 of 58 Photos: Hurricane Irma slams Florida Mario Valentine sits in his badly damaged home in Immokalee on September 11. Hide Caption 16 of 58 Photos: Hurricane Irma slams Florida Boats are partially submerged in Key Largo, Florida, on September 11. Hide Caption 17 of 58 Photos: Hurricane Irma slams Florida Chris Stokes works in the mud as he helps clean up damage to his father's convenience store in Everglades City, Florida, on September 11. Hide Caption 18 of 58 Photos: Hurricane Irma slams Florida Ashley Tomberg drags a tree branch from the roof of a neighbor's house in Gainesville, Florida, on September 11. Hide Caption 19 of 58 Photos: Hurricane Irma slams Florida Floodwaters inundate a car in Jacksonville on September 11. Hide Caption 20 of 58 Photos: Hurricane Irma slams Florida A crocodile appears at the Dinner Key Marina in Miami on September 11. Hide Caption 21 of 58 Photos: Hurricane Irma slams Florida John Duke tries to salvage his flooded vehicle in Jacksonville on September 11. Hide Caption 22 of 58 Photos: Hurricane Irma slams Florida A van sits in a sinkhole that opened up in Winter Springs, Florida, on September 11. Hide Caption 23 of 58 Photos: Hurricane Irma slams Florida People check out floodwaters at Jacksonville's Memorial Park on September 11. Hide Caption 24 of 58 Photos: Hurricane Irma slams Florida Kelly McClenthen and her boyfriend, Daniel Harrison, walk through floodwaters in Bonita Springs on September 11. Hide Caption 25 of 58 Photos: Hurricane Irma slams Florida A truck drives through a flooded street in Key Largo on September 11. Hide Caption 26 of 58 Photos: Hurricane Irma slams Florida A man walks by damage in Palm Shores, Florida, on September 11. Hide Caption 27 of 58 Photos: Hurricane Irma slams Florida Catharine Taylor Woods cleans up a broken awning outside her building in Wauchula, Florida, on September 11. Hide Caption 28 of 58 Photos: Hurricane Irma slams Florida The roof of a home is damaged in Marco Island, Florida, on September 11. Hide Caption 29 of 58 Photos: Hurricane Irma slams Florida Rick Freedman checks damage to his neighbor's home in Marco Island on September 11. Hide Caption 30 of 58 Photos: Hurricane Irma slams Florida Boats are partially submerged in a marina in downtown Miami on September 11. Hide Caption 31 of 58 Photos: Hurricane Irma slams Florida People step out of their flooded home in Fort Myers, Florida, on September 11. Hide Caption 32 of 58 Photos: Hurricane Irma slams Florida A felled tree blocks a street in downtown Miami on September 11. Hide Caption 33 of 58 Photos: Hurricane Irma slams Florida Irma damaged this gas station roof in Bonita Springs. Hide Caption 34 of 58 Photos: Hurricane Irma slams Florida Michele Snelling sleeps on couch cushions next to her 4-month-old daughter, Lauryn, at a middle school in St. Petersburg, Florida, on September 11. The school was filled with evacuees. Hide Caption 35 of 58 Photos: Hurricane Irma slams Florida Hotel guests navigate a dark stairwell after they lost power in Fort Lauderdale, Florida. Hide Caption 36 of 58 Photos: Hurricane Irma slams Florida People in Cape Coral, Florida, tend to a car that flipped over during Hurricane Irma on Sunday, September 10. Hide Caption 37 of 58 Photos: Hurricane Irma slams Florida A manatee lies stranded September 10 after waters receded during Irma's approach in Manatee County, Florida. Hide Caption 38 of 58 Photos: Hurricane Irma slams Florida High winds split this large tree in half in Fort Lauderdale. Hide Caption 39 of 58 Photos: Hurricane Irma slams Florida An American flag is torn as Irma passes through Naples on September 10. Hide Caption 40 of 58 Photos: Hurricane Irma slams Florida A sheriff's deputy walks through a shelter in Naples after the power went out on September 10. Hide Caption 41 of 58 Photos: Hurricane Irma slams Florida A police officer walks over debris after a tornado touched down in Palm Bay, Florida, on September 10. Hide Caption 42 of 58 Photos: Hurricane Irma slams Florida Yaya Lopez holds her fiance, Howard Lopez, while they sleep in a middle-school hallway in St. Petersburg on September 10. Hide Caption 43 of 58 Photos: Hurricane Irma slams Florida Geoff Rutland, a local volunteer from Crossing Jordan Church, helps other residents get ice from a vending machine in Tampa, Florida, on September 10. Hide Caption 44 of 58 Photos: Hurricane Irma slams Florida PJ Pike checks on his boat and one belonging to a friend in Fort Myers. Both were sitting in mud at their moorings due to an unusually low tide on September 10. Hide Caption 45 of 58 Photos: Hurricane Irma slams Florida People walk past a building in Miami where the roof was blown off by Hurricane Irma on September 10. Hide Caption 46 of 58 Photos: Hurricane Irma slams Florida An abandoned car sits in floodwaters during a storm surge in Fort Lauderdale on September 10. Hide Caption 47 of 58 Photos: Hurricane Irma slams Florida Fallen trees block a parking lot in Fort Lauderdale on September 10. Hide Caption 48 of 58 Photos: Hurricane Irma slams Florida Sailboats moored near Watson Island ride out the winds and waves on September 10. Hide Caption 49 of 58 Photos: Hurricane Irma slams Florida Members of the Blinckman family use their personal devices in a stairwell utility closet as Hurricane Irma went over Key West, Florida, on September 10. Hide Caption 50 of 58 Photos: Hurricane Irma slams Florida Evacuees watch the weather from a shelter in Naples on September 10. Hide Caption 51 of 58 Photos: Hurricane Irma slams Florida Heavy winds and rain blow through Miami on September 10. Hide Caption 52 of 58 Photos: Hurricane Irma slams Florida Weather Channel meteorologist Mike Seidel fights fierce winds and flooded streets while reporting in Miami on September 10. Hide Caption 53 of 58 Photos: Hurricane Irma slams Florida A man records the gusty winds going through downtown Miami on September 10. Hide Caption 54 of 58 Photos: Hurricane Irma slams Florida A tree lies on a pickup truck after being knocked down by the high winds in Miami on September 10. Hide Caption 55 of 58 Photos: Hurricane Irma slams Florida Hotel guests eat breakfast by lamplight after the Courtyard Marriott was left without power in Fort Lauderdale on September 10. Hide Caption 56 of 58 Photos: Hurricane Irma slams Florida Part of this crane tower collapsed in Miami on September 10. Hide Caption 57 of 58 Photos: Hurricane Irma slams Florida People sit in the Miami-Dade County Fair Expo Center as Irma approached Miami on Saturday, September 9. See Hurricane Irma's impact on the Caribbean Hide Caption 58 of 58

That's because some islands are extremely difficult to access. Southbound US Route 1 -- the only road connecting the Keys -- is closed, Florida Keys spokesman Andy Newman said.

Large debris is blocking access, and a 150-foot stretch "has some buckling," Newman said.

Crews continued to work to clear US 1. Transportation officials have inspected and cleared some bridges, officials said.

Some evacuees from the Keys will get a chance to lay eyes on the devastation early Tuesday when Monroe County allows residents and business owners in Key Largo, Tavernier and Islamorada to return home.

'It's the worst storm I've ever seen'

But officials urged some evacuated Floridians to be patient and not try to go home yet even though the storm was beyond parts of the Deep South.

"We're asking folks to be patient and remain sheltered in place," said St. Augustine Fire Chief Carlos Aviles.

"Stay off the roads, stay off the streets, let us complete our assessment, clear the roads of water, power lines, trees and then you can get out there and determine what happened to your individual property or your neighborhood," said Fort Lauderdale Mayor Jack Seiler.

The massive storm triggered evacuation orders for 5.6 million people before it made two landfalls in the state Sunday.

The first was over the Florida Keys, and the second, over Marco Island, left the island without water and power, authorities said.

"It's the worst storm I've ever seen," said Bill South of the National Oceanic and Atmospheric Administration.

Irma's deadly trail

Before slamming into to the United States, Irma hit Cuba late Friday as a Category 5 hurricane

On Monday, Cuban state TV announced 10 hurricane related deaths -- meaning Irma killed a total of 36 people in the Caribbean before heading to the US.

This is the first year on record that the continental United States has had two Category 4 hurricane landfalls in the same year.

Last month, Hurricane Harvey devastated much of coastal Texas and killed more than 70 people

Are you affected by Irma? Text, iMessage or WhatsApp your videos, photos and stories to CNN (but only if it's safe to do so): +1 347-322-0415.