“This slow motion of Debbie is going to result in that long duration of heavy rainfall, and could cause potentially catastrophic flooding,” NHC meteorologist Michael Brennan told reporters Wednesday morning. 

With 15 to 25 inches of rain expected across the Southeast, Brennan said the agency was “very concerned about the possibility of life-threatening flash flooding” in cities like Savannah, Ga.; Charleston and Myrtle Beach, S.C., and just west of Wilmington, N.C. 

That level of rain, Brennan said, meant flooding in places that aren’t usually accustomed to it; widespread “inundations of businesses and homes” driving emergency rescues and highways closed from flooding or as roads are “eroded from underneath.” 

Flooding is also worsened by Debby’s winds, which are pushing ocean water up against the low-lying, flood-prone — and slowly sinking — cities of the Southeast, making it even harder for the region’s waterways and sewer systems to drain water into the ocean. 

That dangerous level of rainfall is a direct result of the storm’s slow speed, which has allowed it to all-but-hover in place, giving its winds and rain bands unusual amounts of time to transfer billions of gallons of water from the unseasonably hot waters of the Atlantic to the cities of the Southeast, as The Hill reported. 

And Atlantic hurricanes may be slowing down in general as heat largely trapped by burning fossil fuels strengthens the westerly winds that slow their passage north, according to a 2020 study out of Princeton. 

The result of all that rain is a storm that threatens the Eastern Seaboard with as much as a week of “life-threatening” flooding, Brennan said.  

That risk extends across the coastal Carolinas through Friday, as a Debby strengthened by the Gulf Stream lumbers back onshore Thursday morning, and which will extend across northern North Carolina and “all the way through the mid Atlantic states and into southern New England through Sunday morning,” he added. 

Over the past decade, rain-driven flooding has gone from a small share in total hurricane deaths to the biggest factor, according to a 2023 report by the NHC that Brennan coauthored.  

Between 2013 and 2022, 57 percent of hurricane fatalities came from rain-driven flooding — more than twice the share seen in hurricanes that hit the U.S. between 1963 and 2012. 

Welcome to The Hill’s Sustainability newsletter, I’m Saul Elbein — every week we follow the latest moves in the growing battle over sustainability in the U.S. and around the world.

The pull of the moon helped slow the Earth’s rotation during two distinct periods in the distant past — a shift in the planet’s spin that scientists speculate helped evolve the underwater ecosystems where complex life developed. 

During two prolonged periods between 650 and 280 million years ago, the distance between Earth and its satellite increased by 12,000 miles, driving a more than two-hour increase in the length of the day, according to findings published on Tuesday in PNAS. 

Those periods of increasing day length were a punctuated “staircase” — rather than a gradual, continuous shift, the PNAS researchers found. 

Those periods of sudden (in geologic terms) changes in day-length brought a significant uptick in the amount of light hitting the Earth’s oxygen-exhaling plants — dramatically increasing the availability of an element whose highly reactive nature offered “a major coup for early life forms.” 

The fastest periods of changing day length correlated with a rise of highly energetic oxygen in the atmosphere — which also coincided with two similarly rapid expansions in the diversity and complexity of life, the PNAS study found. 

The first period of day-lengthening overlaps with the bursting forth of new forms of complex animal life in the Cambrian Explosion 550 million years ago — a period when most of today’s animal body plans developed. 

The second corresponds to the vast radiation of species during the Permian and Carboniferous periods, when amphibians rose from the sea to colonize the land, and reptiles and the ancestors of dinosaurs and mammals appeared. 

In another tantalizing detail, the scientists noted, the reason for the lengthening day was the ocean’s greater absorption of the moon’s tides — which could have churned up the ancient seas in ways that helped form oxygen-producing environments.  

This possible connection between the airless, lifeless moon and the Earth’s teeming biosphere is still largely conjecture, “and must be interpreted with care,” the scientists conceded. 

They added that next steps in the research will hinge on getting a more precise date for the surges in the Earth’s oxygen to see how well they correlate with the moon’s impact on the length of the planet’s days.