It’s estimated that Helene killed at least 250 people across seven states, according to a report from the National Hurricane Center. It’s one of the deadliest storms to ever hit our country. The scale was massive.
Here in Appalachia, we typically feel safe from the types of natural disasters that occur closer to the coast. But floods have been increasing here in recent years, and Helene may foretell future flooding events that could impact more Americans.
In this episode, we’ll hear from experts who specialize in studying hurricanes and tropical storms. They explain the science behind Helene, and why this storm was unique, especially for communities in Southwest Virginia, East Tennessee and Western North Carolina.
The mountains of this region have seen impacts from tropical systems before, but a storm on the scale of Helene was unique. Residents and first responders in more inland communities don’t typically worry about these kinds of storms because it's fairly uncommon to see impacts from hurricanes in Appalachia.
But this is something the National Hurricane Center has been working to change in recent years. “So the last mile is getting people to understand that risk and then taking the steps it takes to be prepared, but also being ready to go when the warnings come out, when the flooding is there,” said Ken Graham, who was leading the National Hurricane Center back in 2019, and is now the current director of the National Weather Service. “You can have a perfect forecast – unless it’s actionable, that last mile fails.”
Stephanie Zick is an associate professor at Virginia Tech who specializes in tropical meteorology, and she said from the very beginning, Helene was a large circulation. It formed as part of what’s called a Central American Gyre – which is a little different from how tropical systems in the Atlantic typically form. The “traditional” formation typically occurs with African easterly waves, which are normally pretty small to start off with. Zick said Helene was very large at the beginning of its life cycle.
“And then it stayed big. So, it was pretty large scale in terms of its circulation as it became a named, tropical storm. And then, as it intensified into a hurricane, it was large compared to an average tropical cyclone in the Atlantic,” Zick explained.
Helene being so large allowed it to gather lots of moisture in the days leading up to landfall over the Florida “Big Bend” region on September 27th as a Category 4 hurricane – the strongest landfalling hurricane there for as long as we have records – dating back to 1900.
The storm’s center only moved directly over the western-most edge of North Carolina and still delivered incredible destruction there and in Southwestern Virginia. Historic amounts of rainfall and flooding occurred with Helene because of a number of factors.
Zick and others explained part of why Helene was so destructive is because there was a PRE, or predecessor rain event, ahead of Helene.
“And these happen sometimes as tropical moisture kind of gets funneled in over a landmass,” said Zick. “And they happen before the storm makes landfall and there’s lots of tropical moisture it can tap into, and in the right conditions it can kind of focus it in certain regions. So, there was a frontal boundary draped over the southern Appalachians and this moisture was coming from the tropics and we were able to have lots of rainfall before Helene made landfall. So, the rain event started like three days before the actual Hurricane Helene moved inland.”
So rain was falling in our region before the center of Helene itself even got close to us later on September 27th. All that water saturated the ground, so that when the heavy rain from Helene proper arrived, it essentially had nowhere to go.
Another factor was the mountainous geography in Southwest Virginia. The mountains can make clouds produce more rain.
“Any air mass if it is forced to rise over a mountain, it will tend to become saturated and produce rain,” Zick explained. “So, that’s why you have more rain in the mountains. This is called an orographic effect, and this can happen over the Appalachians as well.”
Zick said Helene was a great example of this phenomenon, which contributed to some of the incredible rainfall rates the storm produced.
“We saw rainfall rates at times of three and four inches per hour,” said Zack Taylor, a meteorologist with the Weather Prediction Center, which produces precipitation outlooks as part of the National Weather Service.
“Much of the region saw between 10 and 20 inches of rain. Some of the highest amounts were of course centered over Western North Carolina, where some locations did exceed 30 inches over the three-day period.”
The National Hurricane Center produces a sort of “after-action report” for hurricanes. That document for Helene showed that more than 60 flood gauges across portions of South Carolina, North Carolina, Tennessee and Virginia reached all-time peaks during Helene.
A number of flood gauges in Western North Carolina and Southwest Virginia exceeded all-time records, including a handful that date back to the 19th century, according to Jason Elliot, the Service Coordination Hydrologist at National Water Center, another arm of the National Oceanic and Atmospheric Administration that focuses on hydrology, which includes things like river levels during heavy rain events.
“So, the New River at Radford, the crest there was 31.03 feet. That was overnight September 27th into the 28th,” Elliot said. “That was the fourth highest crest in history behind 1940, 1916 and then one other event. Down at Allisonia, the crest was 21.91 feet. That gauge actually flatlined for about three hours. It may have reached its maximum limit, we’re not entirely sure.”
In Damascus, the gauge at Laurel Creek actually recorded that the water rose 12 feet in 45 minutes. After that the bridge collapsed, and because the gauge washed downstream with the bridge, it's possible that the actual number was skewed.
Officials with the Virginia Department of Emergency Management said it's possible that the river really did get that high because as water flowed down into Damascus, it brought with it a lot of debris, including several bridges from the Creeper Trail. They say the debris caused Laurel Creek to back up in Damascus, creating a wall of fast-moving water that just slammed against the bridge and washed into the town.
Elliot said the predecessor rain event actually dropped more precipitation in Damascus than Helene itself, but because so much rain fell upstream, it caused the creeks to swell very, very quickly.
Zack Taylor with the WPC said the amount of rain that fell during Helene and the days leading up to the hurricane was statistically unlikely.
“Those values actually ended up being, the probability of it happening was basically one in 1,000,” Taylor said. “So, there was generally a 0.1% chance of that amount of rainfall falling over a three-day period for portions of Southwest Virginia and then obviously down into Western North Carolina.”
Another thing that contributed to Helene’s destruction was the speed at which the storm was traveling. Dan Brown at the National Hurricane Center said Helene had fast, forward moving motion.
“That fast forward motion caused it to bring those winds so far inland,” Brown said. “We don’t often see these hurricane-force gusts penetrate that far inland. We saw it back in 1989 with Hugo, which was a storm that came in off the Atlantic side near Charleston and brought those winds up into parts of Western North Carolina and the kind of central and southern Appalachians. But this one was much more widespread. The topography did play some role, and it was primarily in gusts – very strong gusts that really took down a tremendous number of trees. At the time here, you still had leaves on the trees which probably played a role as well. And then that wet soil from that preceding rain also probably caused more trees to be uprooted.”
Weather experts predict that due to warmer air from climate change, storms like Helene could happen in this region again, and emergency responders and city planners have been trying to figure out how to best prepare for the next Helene.
“So, in terms of hurricanes, we aren’t necessarily expecting to see more storms overall, but we are expecting to see more rapid intensification,” Zick said. “We’re expecting to see larger storms that have more rainfall. If we think about not just hurricanes, but climate change more generally, there’s a lot of confidence that we’re going to have more heat waves and more floods.”
So, theoretically, a larger, even more rainfall intensive storm like Helene is possible in the future...
