By: Lead Forecaster Daniel Crawley
We continue a multi-part series looking back at Hurricane Helene, its evolution and how it turned into the largest natural disaster in the history of Western North Carolina replacing major weather events such as the floods of 1916 and 1940.
Between now and Saturday (Sept 27), the official 1-year anniversary, we will revisit the storm from a forecaster’s perspective here at Foothills Weather Network. We will go over the factors that created a three-day rain event that brought historic flooding to many river basins in WNC along with the impact of strong winds as Helene itself moved in. We will also re-live the post-storm impacts that Helene brought to the region, including several of the counties that we cover daily at Foothills Weather Network.
Today, we look back at the events of September 26th, 2024 from a forecasters point-of-view. For multiple days we had forecasted the potential for a Predecessor Rain Event (PRE) to occur on Wednesday and that did verify as the combination of tropical moisture, a stalled surface front, a stalled upper low and the topography of the Southern Appalachians created a zone of very heavy rainfall.
A near stationary line of heavy rain focused itself on the Eastern Slopes of the Blue Ridge where 6-10 inches of rainfall (some local higher amounts) fell across Polk, western sections of Rutherford, McDowell, Burke, Caldwell Counties and into the mountains of Henderson, Buncombe, Yancey, Mitchell and Avery Counties. With the focus of that rain falling along the Continental Divide, the headwaters of the Catawba, Rocky Broad, Toe River and Swannanoa River Basins took on the bulk of the water.
for September 26, 2024
As a result of the excessive rainfall, flooding started as early as late Wednesday evening and peaked into the morning hours of Thursday putting the Catawba and Broad Rivers at several feet above action stage. Once you got away from the Blue Ridge, the rainfall were less intense as the event was just starting in places like Hickory, Shelby and Lincolnton.
The verification of the PRE further re-assured that the worst was still to come on the next day as Helene itself would make its appearance. Speaking of Helene, the storm was still in a phase of significant intensification. It had become a hurricane on the 25th and now accelerating to the north-northeast, Helene was on the verge of being a major hurricane in the Gulf.
Here locally, while Emergency Management officials were busy with active calls from the PRE, focus also shifted to additional proactive measures to help others who may be impacted down the road. Additional evacuations of flood-prone areas were put into effect during the day as catastrophic flooding was looking more like a reality with each passing minute.
For us in the weather enterprise, the further communication of impacts was paramount to our mission of serving and protecting the public. Foothills Weather Network released another High Impact Briefing around the lunch hour that day going over the continued worries of historic flooding. We also began to pin down the second aspect of Helene and that was the expected high winds. At the time, Helene was projected to make landfall as a Cat 4 hurricane with a forward movement of around 25 mph. Any time a major hurricane moves at that kind of speed, winds impacts are prolonged post-landfall in comparison to slower-moving storms.
Inland Tropical Storm Warnings were issued the day prior by the NWS/NHC and were being updated throughout the day to show both rain and wind potential. As Helene continued to get stronger, the chances of high-end tropical storm force gusts were increasing for the North Carolina Mountains and parts of the Foothills. We highlighted that in our briefing that afternoon.
Once our weather team updated the forecast that afternoon, we continued through social media posts to advise of the significance of what we may see when Helene visited on the 27th.
Due to the rainfall that was still occurring day two into this event, many of the rivers impacted from the PRE was not able to get back below minor flood stage and for those further east, the saturation process was well underway. That was a sobering reality for us at Foothills Weather Network knowing what was to come.
Helene was still accelerating going into Thursday night officially made a landfall just prior to midnight as a 140 mph hurricane
Coming Up: On Saturday we look at the final chapter of this series as we will go over in detail the timeline of September 27, 2024. A day that none of us will ever forget. We’ll go over the metrological aspect of the storm and then tackle into the post-storm reality which included areas being isolated from others and the huge infrastructure failure that occurred and lasted for several days and weeks post-Helene.