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Updated at 9:15 a.m. ET Tuesday, Aug. 8, 2024
The center of Tropical Storm Debby is located near Savannah, Georgia, but is forecast to move over the warm Atlantic waters later Tuesday. The ocean temperatures in that area are very warm, so there will be plenty of energy for Debby to strengthen. Although part of the circulation will remain over land, which should keep it from getting terribly strong.
The back side of the storm is mostly dry, but moisture from the Atlantic is rotating inland on the right side of the circulation. Since the system is only drifting, the fire hose of tropical moisture is drenching the same areas over and over. Already, large parts of the Lowcountry of South Carolina have received 10 inches of rain, with some areas getting 15 inches. Another 10 or 15 inches is forecast where intense rain bands set up. Widespread areas will end up with at least a foot.
Coastal Georgia and the Low Country of South Carolina are traversed by rivers and creeks coming from the Midlands to the north. All the rain that falls at the higher elevations eventually has to go downhill to the Atlantic Ocean. This rain will be far more than those rivers and drainage systems can hold in their banks.
In addition, while the center of Debby’s circulation is offshore, the wind flow on the eastern side will push the Atlantic waters toward the coast. The pressure from that storm surge will prohibit the river water from draining normally, dramatically increasing the flood threat in coastal sections. Flooding from just the storm surge is forecast to be up to 4 feet above normal high tide in some locations along the Carolina coast.
This is an extremely dangerous flooding scenario. It’s critical that everyone in the storm zone listens for information and instructions from local officials.
Debby is still drawing tropical moisture over the Florida peninsula, so heavy downpours are still possible for the next few days.
There is good consensus now that by Friday, Debby will move to the northeast over North Carolina and up the East Coast. It will merge with a cold front, creating a heavy rain scenario Friday and Saturday over an extended area, if the forecast is correct. It won’t be a tropical system when it’s over the mid-Atlantic or the Northeast, but the combination of cool air from the north and tropical air from the south can cause intense rainfall.
As with all slow-moving systems, the forecast is subject to change, but unlike the last few days, the various computer forecasts generally agree that Debby, or what’s left of it, will be scooped up and pulled to the north at the end of the week.
Elsewhere in the tropics, a tropical disturbance in the eastern Caribbean has a slight chance of developing into a tropical depression in a few days. If it does develop, it would likely be in the western Caribbean or the extreme southern Gulf of Mexico. The National Hurricane Center has its development chances in the low category.
High pressure across the southern U.S. should keep the system well to the south and tracking west whether it develops or not.
More disturbances are moving off of Africa, but there is still a lot of dry air over the Atlantic. We’ll see if moisture takes over, like it normally does, around the middle of August.