Catastrophic flash flooding and major river flooding is only expected to mount across North Carolina and northern South Carolina in the wake of Florence.

"Flooding has become catastrophic in some areas and access to some communities will only be possible by boat into later this week," according to AccuWeather Senior Meteorologist Mike Doll. "This is truly a life-threatening situation."

The number of flash flood emergencies, water rescues, evacuations and road closures continue to rise. Florence is already being blamed for the deaths of at least 18 people.

Floodwaters from Florence inundate the town of Trenton, N.C., Sunday, Sept. 16, 2018. (AP Photo/Steve Helber)

AP Photo

It may take 1-2 weeks for all of the runoff to drain slowly downstream from the mountains to the coast.

"For this reason, river flooding is sometimes called a slow-moving natural disaster," AccuWeather Senior Meteorologist Alex Sosnowski stated.

The Northeast Cape Fear, Pee Dee, Lumber and Waccamaw rivers are among those projected by National Weather Service Hydrologists to be at major flood stage through most of the week.

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Record crests will be challenged or shattered in some communities.

The gauge for the Northeast Cape Fear River near Chinquapin, North Carolina, was topped after the river rose past the previous record crest of 23.5 feet. The river is expected to continue to rise to 28.2 feet into Monday.

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Homes, businesses and land can be underwater even as sunshine returns.

Showers and thunderstorms will persist across the Carolinas Monday into Tuesday. While there can still be downpours that can aggravate flooding or delay flood waters from receding, such issues would be more localized than this weekend.

Much-needed dry weather will finally dominate during the middle to latter part of the week. Warm and humid conditions, however, will put a strain on recovery crews and residents without power and air conditioning.

Even as floodwaters recede, washed out and damaged roads and bridges can further prolong the region’s return to normalcy.

"The drinking water in some areas can become contaminated," according to Doll. Standing water can also serve as breeding grounds for mosquitoes and other insects.

"Utility outages may last for weeks, especially for coastal communities," Doll stated.

The unfolding natural disaster is projected to take a costly toll on property.

"AccuWeather estimates that Florence will cause $30-60 billion in economic impact and damage. To put this in context, we correctly predicted the full extent of Hurricane Harvey’s economic damage to be $190 billion last year. While we expect an AccuWeather Local StormMax™ of 40 inches of rain, extensive inland flooding and storm surge flooding from Florence, Hurricane Harvey unleashed more than 60 inches of rain locally centered around the United States’ fourth largest city, Houston, which has a population of 2.3 million,” AccuWeather Founder and President Dr. Joel N. Myers said.

"For further context, we accurately estimated the total economic impact from Hurricane Irma would be $100 billion. Additionally, Florence’s projected toll is less than Hurricane Sandy's toll of $69 billion and Katrina's cost of $161 billion," Myers said.

"Other sources are predicting a financial toll for Florence of up to $170 billion, and we think that is extreme when looking at Florence’s track and impacts to people and their lives. Florence made landfall in North Carolina as a Category 1 storm Friday morning. Storms of this magnitude have struck the U.S. coastline in the past, in some cases causing $10 billion or less in total damage,” Myers said.

Florence has already unloaded more than 20 inches of rain as of early Monday morning with at least two preliminary rainfall total in excess of 30 inches.

If 40 inches of rain falls, it will be the heaviest amount of rain from a single storm in the Lower 48 states since Hurricane Harvey last year.

Prior to Florence, North Carolina’s tropical rainfall record was 24.06 inches set during Hurricane Floyd in 1999.