After moving ashore Florida’s Big Bend yesterday around daybreak as a Category 1 hurricane, Debby has crept through north Florida and southeast Georgia slower than most of us can run.
The result has been tremendous rainfall totals over the past 24 hours – over a foot estimated by radar centered on the Live Oak and Lake City areas of north-central Florida and again from Savannah to south of Charleston in coastal Georgia and South Carolina.
Numerous flash flood warnings were ongoing, including in downtown Charleston, where water filled the streets as strong onshore winds gusting to 45 mph and a persistent storm surge from Debby’s nearby circulation compounded high water drainage issues.
Today marks the start of a prolonged and likely catastrophic flood event
Debby is trapped in a very weak steering environment, a scenario prone to prolific rainfall that we previewed as early as last Thursday in this newsletter. Though the storm is expected to scoot back over water off the southeast today, with some restrengthening forecast, the main effect this will have is reloading the storm with rich, tropical moisture and keeping a strong and persistent onshore flow into local tributaries, which will make natural drainage of floodwaters slow or difficult.
The weak steering will act like a game of Plinko for Debby as it bounces around along the southeast coastline or just inland, bringing round upon round of tropical rainfall across many of the same areas through Friday.
The National Weather Service is calling for a high risk of excessive rainfall, its most dire rain forecast category, for an unprecedented three consecutive days, a move that further signals the severity of the severe and prolonged flood event that will stretch deep into the week. High risk days are a big deal and account for the majority of flood-related damages and over a third of all flood-related fatalities each year.
The highest flood threat extends from southeast Georgia to eastern Carolina, and by Thursday, could overspread the Piedmont of North Carolina as far north as the Raleigh-Durham Research Triangle.
National Weather Service officials are characterizing the upcoming flood threat as historic, unprecedented and catastrophic. As we discussed in our Sunday newsletter, up to 25 inches of additional rainfall would rival state rainfall records in Georgia in South Carolina.
What we’re watching behind Debby
Debby will finally move out by the weekend, although flood issues, especially along local rivers, will linger in its wake.
A healthy tropical disturbance we’ve been following continues to move deeper into the Caribbean. It’s been moving too quickly for sustained development but some development is possible as it nears Central America late tomorrow and on Thursday. The good news is it will be moving inland quickly so significant development is unlikely.
The disturbance is moving far south and poses no threat to South Florida, nor does it appear to be a threat to the broader U.S. or Texas at this time.
The Atlantic will stay in a broadly conducive configuration for tropical development for the remainder of August so we’ll need to continue to track the incoming systems from the eastern Atlantic. We’re seeing hints in our forecast models of another strong disturbance approaching the eastern Caribbean islands in a week or so, but at least for now no additional U.S. threats are looming for the next 7 days.