Debby formed into a tropical storm on Saturday and turned northward toward the Big Bend of Florida. It is getting better organized and is likely to become a hurricane before making landfall midday Monday. Winds will be a concern in northern Florida near where she makes landfall, but it is the rainfall that will be the bigger problem.
At 5:30 p.m. Sunday Tropical Storm Debby could be seen from the National Weather Service Raday in Tampa, Florida. Its maximum sustained winds were 65 mph, and it was moving north at about 12 mph. Rain was already impacting parts of Florida with flooded roadways and neighborhoods. A storm surge and high winds will occur near the landfall.
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| The radar image from NWS Tampa as of 5:30 pm EDT, Sunday August 4, 2024. The blue circle west of Tampa represents the center of Tropical Storm Debby. Note the banding over the Gulf of Mexico as the system gets better organized. Substantial rain was already falling over the Florida peninsula. |
Debby is moving northward between two large high-pressure systems. One is located to the northwest over the central U.S. and the other is the Azores-Bermuda high to the east. A trough of low pressure along the East coast of the United States has produced a weakness in the pressure field allowing the storm to turn north. However, the trough will move out before the storm makes its way up the eastern seaboard leaving the storm in very weak steering currents. This will allow it to slow to a crawl and potentially stall along the South Carolina coast on Wednesday.
The current forecast (5 pm EDT Sunday) from the National Hurricane Center is for Debby to take nearly 48 hours to move from near Jesup, Georgia to Folly Beach, South Carolina. That is about 135 miles and takes about three hours to drive, but for Debby it may take 2 days.
The forecast for Tropical Storm Debby as of 5 pm EDT, Sunday August 4, 2024, from the National Hurricane Center. Note to very slow movement from Tuesday to Thursday afternoon.This is why the coastal areas will receive so much rain.
Abundant moisture will be pumped into southeastern Georgia and coastal South Carolina by the circulation of the storm. Rainfall is likely to be substantial with the greatest threat of flash flooding occurring Tuesday and Wednesday.
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| This is the threat of excessive rainfall outlook from Tuesday morning to Wednesday morning. Flash flooding the purple area is very likely. |
The slow movement of Debby means that rainfall impacts may last into next weekend. The rainfall forecast by the Weather Prediction Center for the next seven days puts rainfall in the 50-to-100-year category for the low country of South Carolina. The graphic below shows the total rainfall for the next 7 days. Keep in mind that you will lower amounts in some forecasts, but they are for a shorter period of time.
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| This is the forecast of total rainfall over the next 7 days. Rainfall will intermittent with the heaviest on Tuesday and Wednesday. However, rainfall will be likely every day into the weekend. The total amount will likely cause flooding of most rivers. The maximum total rainfall will likely be near Beaufort, South Carolina and could exceed 2 feet of rain. |
I chose the 7-day forecast, because it is not just the heaviest rain that is a concern. During this time Beaufort, South Carolina could see over 2 feet of rain. I am certain that there will be flooding in the coastal areas of Georgia and South Carolina. However, even Orangeburg could see over a foot and Columbia could see over 9 inches of rain. Thus, flash flooding is possible in those areas as well. In fact, there will be a high risk of flooding for all areas in South Carolina south of I-20 and in the north coastal areas.
We have seen floods in parts of South Carolina over the past decade: The Great Flood of 2015, Hurricane Matthew in 2016 and Hurricane Florence in 2018. This has the potential to be near those totals over a 7-day period.
THE FORECAST
There is a lot of uncertainty in the forecast beyond 48 hours. The reason is that whenever a storm stalls it is difficult to predict how long it will stay in the area and how much rain will fall. The forecast for Beaufort could be anywhere from 15 to 30 inches simply based on the movement of Debby. In 2017 Hurricane Harvey was forecast to dump up to 35 inches of rain north of Houston but dumped more than 60 inches. It wasn’t a bad forecast, just a minor change created a bigger problem.
YOU CAN EXPECT THE FORECAST TO CHANGE. Yes, we know the storm is coming, but minor changes can have big results. You need to check the updated forecast for everything you do. Debby will be a big problem for the entire workweek.
It may seem strange to have the storm move into the Big Bend area and then slowly move toward the Savannah area. Historically this has happened before. I have seen systems move across north Florida and emerge off the Georgia coast and stall. This part of the forecast seems reasonable.
A PLAN
Have a plan for everything you do this week. If you must travel through the area, check the latest roads conditions and whether heavy rain is occurring.
FOR GOD’S SAKE DO NOT DRIVE INTO FLOODED ROADWAYS!
I saw this so much in the Flood of 2015. People could see the road flooded and the cars that had stalled trying to get through and yet they still drove into the flood. Over 500 roads were close to flooding and there were over 250 water rescues into the Columbia area alone. This puts too many people in harm's way. As the National Weather Service says, “turn around, don’t drown.”
I have given you an overview of what I expect to happen this week. It is up to you to keep up with the latest developments. Please think before you act. Local meteorologists are working hard to keep you up to date.
