Florence strengthens to Category 4 hurricane, SC coast to be evacuated
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WATCH: A state of emergency has been declared from Maryland to the Carolinas as the Category 4 hurricane bears down on the U.S.

Hurricane Florence, packing winds of 140 mph, has quickly strengthened to a dangerous and powerful Category 4 storm as it takes aim at the East Coast.

The storm will likely make landfall Thursday evening in North Carolina.

Bringing a devastating storm surge, powerful winds and catastrophic flooding, governors in South Carolina, North Carolina, Virginia and Maryland are urging residents to prepare.

About 1 million people have been ordered to flee the entire South Carolina coast beginning at noon on Tuesday.

"It's going to be inconvenience but we don't want to risk one South Carolina life in this hurricane," South Carolina Gov. Henry McMaster said Monday.

Weather graphic shows the latest Hurricane Florence forecast.
Jim Craig, David Burke and Chris Rayner load generators as people buy supplies at The Home Depot on Monday, Sept. 10, 2018, in Wilmington, N.C.

The biggest threat from Hurricane Florence is the extreme and potentially catastrophic rainfall forecast

Because Florence is expected to stall after landfall, the rain is forecast to hit the same area for a long period of time.

Rain totals may climb over 20 inches in parts of inland North Carolina and Virginia.

Weather graphic shows Tropical rainfall due to Hurricane Florence.

"We here in North Carolina are bracing for a hard hit," North Carolina Gov. Ray Cooper said at a news conference Monday.

The state has issued mandatory evacuations.

"This storm is strong and it's getting stronger," Cooper said.

The state is "taking Hurricane Florence seriously and you should too. Get ready now," he said. "The best safety plan is preparation and common sense."

An evacuation order for visitors and residents on Hatteras Island is in effect Monday while those in other parts of Dare County will be under an evacuation order beginning Tuesday.

Boarded up houses are seen ahead of Hurricane FlorenceÃ?s expected landfall, at Holden Beach, N.C., Sept. 10, 2018.

In Maryland, Gov. Larry Hogan is urging residents to be prepared for "possible catastrophic and life threatening flooding."

"Start now, and prepare your families and your homes," he said Monday.

Weather graphic shows the latest Hurricane Florence forecast.

President Donald Trump exhorted residents to follow officials' instructions.

"The Storms in the Atlantic are very dangerous. We encourage anyone in the path of these storms to prepare themselves and to heed the warnings of State and Local officials," he said in a tweet. "The Federal Government is closely monitoring and ready to assist. We are with you!"

Hurricane Florence this morning as seen from Space Station.

Florence is just one of several storms brewing.

Hurricane Helene is a Category 2 storm but is expected to go out to sea with no threat to land.

Hurricane Isaac is moving toward the Caribbean and could make landfall Thursday as a Category 1 hurricane.

Men use ropes to pull away the debris of houses in order to look for bodies, after the Galveston Hurricane of 1900. The Category 4 storm with winds in excess of 130mph and a storm surge of over 15 feet, was the... Photo Credit: Library of Congress/Corbis/VCG via Getty Images
Homes in Cameron, Louisiana, lie in ruins in the wake of Hurricane Audrey, July 1, 1957. As far at 25 miles inland were inundated with storm surge of 8 to 12 feet, and leaving 390 dead. Photo Credit: Beaumont Enterprise/AP Photo
U.S. Highway 90 at Biloxi went under several feet of water as powerful Hurricane Betsy slammed into the mainland, Sept. 10, 1965. At left in the background, a National Guard truck makes its way through the wate... Photo Credit: AP Photo
Father William Pittman, left, conducts an outdoor Mass outside the ruins of St. Thomas Catholic Church at Long Beach, Mississippi, Aug. 24, 1969, just one week after Hurricane Camille took a heavy toll on the M... Photo Credit: Jack Thornell/AP Photo
Pennsylvania Gov. Milton Shapp, front right, in Harrisburg, Pennsylvania, surveys the damage. He and his wife Muriel evacuated earlier from the governor's mansion after Hurricane Agnes flooded the area, June 23... Photo Credit: Patriot News/AP Photo
Kitty Hicks salvages a few items from her home in Hemby Bridge, Nort Carolina, Sept. 29, 1989. The house was destroyed by a tree during Hurricane Hugo. The Category 4 hurricane made landfall just north of Charl... Photo Credit: Davie Hinshaw/Charlotte Observer/AP Photo
Homes were reduced to piles of rubble following Hurricane Andrew in 1992. Wind-recording instruments were destroyed in the peak areas, and others recorded gust of up to 177 mph, making it one of the most inten... Photo Credit: Steve Starr/Corbis, via Getty Images
Charles Summers, resident of Oak Island in the coast of North Carolina near Wilmington, walks next to a house that was destroyed by strong winds and the rising surf produced when Hurricane Floyd touched down a ... Photo Credit: Roberto Schmidt/AFP/Getty Images
The surf pounds a mobile home park sitting on the Indian River at Jensen Beach, Florida, as Hurricane Frances moves through the area, Sept. 4, 2004. Though only a Category 2 storm when it made landfall near Stu... Photo Credit: J. Albert Diaz/Miami Herald, via AP Photo
An aerial view of wrecked homes in Punta Gorda, Florida, after Hurricane Charley battered the town with 145 mph winds, Aug. 13, 2004. What started as a tropical wave, grew into a hurricane with strengthened int... Photo Credit: John Roca/NY Daily News Archive via Getty Images
Water spills over a levee along the Inner Harbor Navigational Canal in the aftermath of Hurricane Katrina, Aug. 30, 2005 in New Orleans. Storm surge flooding of 25 to 28 feet above normal in Mississippi and 10 ... Photo Credit: Vincent Laforet-Pool/AFP/Getty Images
Evelyn Turner cries alongside the body of her longtime companion, Xavier Bowie, after he died in New Orleans, Aug. 30, 2005. Bowie and Turner had decided to ride out Hurricane Katrina when they could not find a... Photo Credit: Eric Gay/Associated Press
A road collapsed following Hurricane Ike, Sept. 15, 2008, in Galveston, Texas. The storm produced tropical-storm-force winds extending 275 miles and made landfall as a Category 2 hurricane in Texas and then con... Photo Credit: Scott Olson/Getty Images
Homes in the Rockaway neighborhood were damaged during Hurricane Sandy, Oct. 31, 2012, in the Queens borough of New York. The tropical cyclone merged with another system creating an extra-tropical cyclone, thus... Photo Credit: Spencer Platt/Getty Images
A roller coaster sits in the Atlantic Ocean after the Fun Town pier it sat on was destroyed by Superstorm Sandy, Nov. 1, 2012, in Seaside Heights, New Jersey. Photo Credit: Mark Wilson/Getty Images
Branches litter an alley as a result of Hurricane Irene, Aug. 28, 2011, in Virginia Beach, Virginia. The Category 1 hurricane struck the Outer Banks in North Carolina first, weakened, struck New Jersey and the... Photo Credit: Brendan Hoffman/Getty Images
Rescue boats fill a flooded street as people are evacuated from rising water after Hurricane Harvey, Aug. 28, 2017, in Houston. Making landfall in Texas on Aug. 25, Harvey was the first major hurricane to hit t... Photo Credit: David J. Phillip/AP
Floodwaters from Hurricane Irma recede, Sept. 13, 2017, in Middleburg, Fla. A Category 4 hurricane, Irma became the first hurricane to make touch land in Florida since 2004. Due to the amount of damage caused, ... Photo Credit: Sean Rayford/Getty Images
An aerial view shows the flooded neighborhood of Juana Matos in the aftermath of Hurricane Maria in Catano, Puerto Rico, Sept. 22, 2017. The storm has left 97% of the island's 3.4 million residents without elec... Photo Credit: Ricardo Arduengo/AFP/Getty Images

Isaac is forecast to stay south of Puerto Rico but may bring some rain to the island.

In the eastern Pacific Ocean, forecasters are keeping a close watch on Tropical Storm Paul and Tropical Storm Olivia. Paul is not expected to make landfall but Olivia could threaten Hawaii.

Olivia, which weakened to a tropical storm Monday afternoon, will approach Hawaii Tuesday night into Wednesday.

The storm may bring landslides, up to 20 inches of rain and flash flooding for the Hawaiian Islands.

ABC News' Josh Hoyos, Jason Volack, Amanda Maile and Chris Donato contributed to this report.