Tropical Storm Debby is expected to bring flooding to the Southeast. Here’s how much rain could fall

Northern Florida, coastal regions of Georgia and South Carolina, and parts of North Carolina are bracing for heavy rain and catastrophic flooding this week as Storm System Debby moves eastward.

Debby made landfall as a Category 1 hurricane on Florida’s Big Bend coast early Monday, first striking the small community of Steinhatchee. It damaged homes and businesses, caused flooding and power outages across the state and Georgia, and resulted in several deaths. Debby was downgraded to a tropical storm midday Monday.

But experts say the worst is yet to come as the storm system is expected to stall over the Southeast region.

How much rain is expected?

Forecasters say the system could lash the Southeast with widespread areas of up to 20 inches (51 centimeters) of rain and some totaling up to 30 inches (76 centimeters).

That would be a record rainfall amount, surpassing the record for a tropical system during Hurricane Florence in 2018. More than 23 inches (58 centimeters) of rain was recorded in South Carolina after that storm hit the Carolinas.

Although Debby was classified as a Category 1 disaster, “it really deserves a Category 3 or 4 rating, if you’re talking about rainfall impacts,” said Jeff Masters, founder of Weather Underground, now at Yale Climate Connections. “That’s going to cause a lot of damage.”

What areas are at risk?

The most severe flooding is expected in northern Florida, as well as low-lying areas such as Savannah, Georgia, Hilton Head Island and Charleston, South Carolina. North Carolina could also be affected.

Savannah officials warned that the area could receive a month’s worth of rain within four days if the system stalls. There are also concerns of possible flooding on Tybee Island, Georgia’s largest public beach, 18 miles (28.97 kilometers) east of Savannah. In addition to torrential downpours from Debby, the island could become even wetter from a storm surge of 2 to 4 feet (60 to 120 centimeters), according to the National Hurricane Center.

“We don’t know how much rain we’ll get, but we have to prepare for the worst,” Hilton Head Island Mayor Alan Perry said in a video posted on Facebook. “If that happens, we’ll see a phenomenon we’ve never seen before on Hilton Head.”

Meanwhile, Charleston County Interim Emergency Director Ben Webster called Debby a “historic and potentially unprecedented event” three times in a 90-second briefing Monday morning.

Few places in South Carolina are as susceptible to flooding as Charleston. Much of the city and surrounding areas, founded in 1670, were built on land created from fill dirt and other debris. Rising sea levels cause a number of minor floods even without storms, and like many coastal cities, Charleston does not have good drainage.

The city does not expect a significant amount of flooding from the ocean, but the storm is still dangerous. Heavy rains could accumulate in the city and cause flooding.

What is causing this storm to stop?

Some hurricanes make landfall and move quickly, experts say, while others slow down considerably.

“What actually happened and why the storm stalled is because there are basically areas of high pressure to the west of the storm and to the northeast, and that has kind of kept it trapped,” said Phil Klotzbach, a senior research scientist in the Department of Atmospheric Sciences at Colorado State University. “With a hurricane you always have wind issues, but when you have a storm moving at 3 to 5 miles per hour, it’s going to be over a specific location for a very long period of time, so you’re very likely to have flash flooding and massive amounts of rainfall.”

Experts say atmospheric warming plays a role in the severity of storm surges like Debby.

Warming waters in the northeastern Gulf of Mexico are increasing Hurricane Debby’s heavy rainfall as more moisture evaporates from the waters, Masters said. Some research indicates that climate change may affect the progress of hurricanes, he added, making them slower.

“It’s something we’ve been seeing more of lately,” Masters said.

How long could this last?

The worst of the rain is expected during the first half of the week but could last into Saturday, forecasters said.

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St. John reported from Detroit. Jeffrey Collins contributed from Columbia, South Carolina. Russ Bynum contributed from Savannah, Georgia.

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Alexa St. John is a climate solutions reporter for the Associated Press. Follow her on X, formerly Twitter, @alexa_stjohnContact her at [email protected].