When it comes to the chances another Helene-like storm could hit the Carolinas in the future, it's really a matter of when and not if. Could it be in another 100 years? Another 500 years? Another 1,000 years? Or could a changing climate dramatically increase the reoccurrence of these events?
This week on the Carolina Weather Group, Corey Davis, the assistant state climatologist for North Carolina, explains why a 1-in-1000-year event like Helene could happen again much sooner.
The widespread flooding washing over – and washing out – towns and roadways after Helene was uncomfortably similar to the scenes in eastern North Carolina following Hurricane Matthew in 2016 and Hurricane Florence in 2018. And once again, the major city in the region – Wilmington then, Asheville now – had its interstate connections severed by the flooding.
In addition to those similar impacts, one way of comparing events on opposite ends of the state is using rainfall return intervals, which frame a specific amount over a certain duration as the likelihood of occurring in any given year, such a 1-in-100 year event, with a 1% chance of occurring.
While imperfect due to its lack of recent updates, the most comprehensive return frequency data comes from NOAA’s Atlas 14 product. That showed totals from Hurricane Floyd in 1999 and Potential Tropical Cyclone Eight earlier this summer as roughly 1-in-500 year events, with the totals in excess of 30 inches during Florence classified as worse than 1-in-1000 year events.
Helene's daily rainfall total of 11.89 inches in Celo equals the 1-in-500 year total per Atlas 14. In Asheville, the three-day total of almost 14 inches goes well beyond the 1-in-1000 year total for a 72-hour period, which Atlas 14 cites as 11.4 inches. Likewise, the 24.41 inches over three days at Mount Mitchell is off the charts compared to the noted 1-in-1000 year amount of 16.5 inches.
Yet another event of this magnitude within the state offers even more evidence that our climate is changing, and in extreme ways. The rapid intensification of Helene over the Gulf, the amount of moisture available in its surrounding environment, and its manifestation as locally heavy – and in some cases, historically unheard of – rainfall amounts are all known side effects of a warmer atmosphere.
Read more from Corey on their climate blog: https://climate.ncsu.edu/blog/2024/09/rapid-reaction-historic-flooding-follows-helene-in-western-nc/
Or see what state climatologist Dr. Kathie Dello co-wrote on the topic: https://www.wcnc.com/article/tech/science/climate-science/why-historically-rare-storms-carolinas-geography-climate-change/275-cea5e372-2ca1-454d-ab5a-8d94fcc94d55
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The Carolina Weather Group operates a weekly talk show of the same name. Broadcasting each week from the Carolinas, the show is dedicated to covering weather, science, technology, and more with newsmakers from the field of atmospheric science. With co-hosts across both North Carolina and South Carolina, the show may closely feature both NC weather and SC weather, but the topics are universally enjoyable for any weather fan. Join us as we talk about weather, the environment, the atmosphere, space travel, and all the technology that makes it possible.
