“Life-threatening, catastrophic flash flooding and significant river flooding is likely over portions of the Carolinas and mid-Atlantic states from late this week into early next week,” the National Hurricane Center said, adding that some regions could see up to 89 cm of rain.
Heavy rainfall and inland flooding are typical features of tropical cyclones, but an array of aggravating circumstances mean the flooding damage caused by Hurricane Florence could be worse than that seen in decades in the southeastern U.S.
WATCH: Hurricane Florence to hit Wilmington by late Wednesday
In Virginia, heavier-than-normal summer rains already left rivers swelling and grounds saturated with rainwater, the News Leader reported, citing officials from the Virginia Department of Emergency Management.
That means the potential for flooding in the area is further exacerbated, with National Weather Service officials saying flooding could begin quickly.
Maryland also saw a summer of record rainfall, leaving it more water-logged than usual and prone to catastrophic floods.
Maryland Gov. Larry Hogan said his state was bracing for “the potential of historic, catastrophic and life-threatening flooding,” even though the state was predicted to miss the worst of the storm according to the Tuesday evening forecasts.
WATCH: Battered by recent flooding, Maryland city braces for Florence
Washington too is located away from the predicted centre of the storm, but the state received around 117 cm of rain this year — the fourth-most on record in 146 years, according to the Washington Post.
Like Virginia and Maryland, Washington’s rivers too are already swollen and its soil saturated, increasing the potential for flooding.
Meanwhile, in North Carolina, Hurricane Florence is set to unleash heavy rains on areas that are still yet to recover from the flooding caused by Hurricane Matthew two years ago, according to Wilmington, N.C. newspaper Star-News, with some areas expecting a foot or more of rain.
WATCH: Emergency preps before Hurricane Florence hits Carolinas, Virginia
Rainwall levels could also be higher due to the unusually warm temperatures of the ocean waters that lie below the hurricane. The waters are 1.5 degrees warmer than normal, according to University of Miami hurricane expert Brian McNoldy, and the air is holding 10 per cent more water that can be dumped as rain.
In other words, Hurricane Florence is set to be only the latest example of climate change, specifically rising ocean temperatures, increasing the severity of storms.
2017’s Hurricane Harvey was fueled by hotter-than-usual conditions that caused an increase in evaporating moisture, feeding the hurricane more water to dump on the Gulf of Mexico, according to a study published in the journal Earth’s Future.
“While hurricanes occur naturally, human‐caused climate change is supercharging them and exacerbating the risk of major damage,” the scientists wrote.
Heavier rainfall in turns boosts the prospect of “overwash,” in which storm surge waters over beaches and dunes and damage the communities behind them.
The chances of overwash are deemed “very likely” for 20 per cent of beaches in Virginia, 15 per cent in North Carolina and 12 per cent in South Carolina, according to the U.S. Geological Survey.
Storm surges won’t overtop protective dunes at first, according to the USGS, “But if the storm lingers, and if high surge, higher than normal tides and strong waves persist over a period of days, the likelihood increases that the dunes could be overtopped and flooding could occur behind them.”
WATCH: Officials urge people in North Carolina to heed warnings on Florence
In addition to the immediate threat to lives and property, flooding could also present longer-term hazards if it floods industrial sites such as coal ash dumps and hog manure pits, creating dangerously toxic brews that could wash into homes and threaten drinking water supplies.
The Environmental Protection Agency said Tuesday that it would be monitoring nine toxic waste cleanup sites near the Carolinas’ coast for potential flooding.
The National Hurricane Center increased its rainfall forecast to 38 to 64 cm of rain on Tuesday afternoon, but warned that some places could get 89 cm.
However, a computer simulation known as the European model predicts over 1.1 metres in some regions.
It’s the same model that accurately predicted that 2017’s Hurricane Harvey would drop 1.5 metres of rain.
— With files from the Associated Press
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