Key Points:
- As of 5 p.m., a tropical storm watch and storm surge watch was issued for areas north of South Santee River into North Carolina. A tropical storm warning and storm surge warning remains in effect for areas south of South Santee River in South Carolina.
- Much of South Carolina will see excessive rainfall from Debby, with a historic rain and flooding event along much of the Coastal Plain.
- The most severe and potentially catastrophic flooding will occur across the Lowcountry, where storm total rainfall through Friday will exceed 20 inches, rivaling or exceeding 2015's severity. Both flash flooding and river flooding will be severe.
- Rainfall will also be intense across the Central Savannah River Area, Midlands, and Pee Dee, leading to flash and river flooding. Major river flooding is possible in Debby's wake.
- While rainfall will be less in the Upstate, there will be a risk of isolated flash flooding.
- Coastal flooding from storm surge and above-average astronomical tides will likely affect some or all our coast Tuesday through Thursday. These factors will exacerbate the flooding problems along our coast. The magnitude of the storm surge along the Grand Strand will depend on how strong Debby gets before making landfall there and the storm's exact track.
- While tropical storm force winds will mostly remain confined to our coast through Wednesday, locally strong gusts further inland may cause isolated damage. Over the eastern part of the state, higher-end tropical storm force winds will likely cause more widespread damage Wednesday night into Thursday.
- Isolated tornadoes can occur over coastal areas through Thursday.
Debby made landfall this morning in Florida and is now back to tropical storm strength, creeping northeastward toward South Carolina. The forecast track continues to call for the storm to slowly drift northeastward through Wednesday night, with the center passing over the Atlantic for a time before it turns north and makes a second landfall along the Grand Strand on Thursday morning or midday. There is little change from Sunday.
Our primary threat from Debby remains extreme rainfall and tremendous flooding since it will just be toddling northeastward near our coast. Not much has changed with our rainfall forecast from Sunday; historic rain will lead to catastrophic flooding over much of our Coastal Plain.
As discussed yesterday, this will be 2015-like across much of our Coastal Plain, with some areas that didn't see the most extreme rainfall back then getting more rain from this event. Other areas may see less; no two storms are exactly alike. While the severe flooding can't be pinpointed yet, we expect to see widespread major flooding, both with flash and river flooding. The risk for significant flooding extends well away from the coast, to the I-20 Corridor, and even north of there in the upper Pee Dee region. Areas farther northwest see less rain, but there can still be isolated flash flooding in parts of the Upstate and the Catawba River Area (if you're new here, by that I mean York, Chester, and Lancaster Counties ... a whole different region of SC, IMO, not really the Upstate and not really the Midlands).
Storm surge is a thing for our coastal areas, too. Right now, we think the storm surge will peak at 2-4 feet along our coast. There's a chance for it to be a little higher along the Grand Strand, depending on whether Debby wanders far enough out over the Atlantic and stays there long enough to gain a lot of strength. The timing of the worst surge relative to the tide cycle is in question, too. There is potential for major storm surge flooding should the worst surge hit your area at high tide.
It wouldn't hurt to check out the flooding prep and safety tips from ready.gov.
Damaging winds are one of the lower concerns for South Carolina, but they are a worry. It looks like sustained tropical storm force winds will remain confined to areas along and near the coast Tuesday through Wednesday as Debby moseys northeastward off the Lowcountry coast. A few stronger gusts may down a tree or power line here and there further inland, maybe up to I-20. After turning toward the Grand Strand and strengthening Wednesday night, those stronger winds push into the Grand Strand and further inland across the Pee Dee region. How strong they will get will depend on how much strength Debby gains over the Atlantic. Right now, we think winds will at least reach the strong tropical storm force range (50 knots, 58 mph), which would be enough for a good bit of tree and power line damage over the eastern part of the state, especially along the Grand Strand. I can't rule out Debby reaching hurricane strength again before reaching our coast, which would result in even more damage potential.
Our coastal areas will be dealing with an isolated tornado risk as well. As of press time here, we have a tornado watch out across the Lowcountry, in effect until 1:00 a.m. Tuesday.
You can expect to see more tornado watches issued that cover some or all of our Coastal Plain through Thursday. Stay alert for them and tornado warnings that may come out for your area. You'll want to have a plan to get to shelter should a tornado threaten your area and have the plan ready in advance. Especially with tropical cyclones, sometimes you don't get much lead time with tornado warnings.
By now, all your hatches should be battened with pouring rain falling over most of the state already. But you could still, with caution, get out and take care of prep needs this evening and even Tuesday over much of the state that will see major impacts. If you need help figuring out your needs, you can always visit hurricane.sc.
We continue to monitor a tropical wave in the eastern Caribbean Sea, which NHC gives a 30 percent chance to develop over the next week. However, most of today's computer models indicate it will stay well to our south and west. That's how we like it.
This loop of GeoColor visible satellite images shows a tropical wave generating clouds over the eastern Caribbean Sea.
Imagery Source: SLIDER by RAMMB from CIRA at Colorado State University
