How Helene’s Floodwaters Devastated Southeastern United States

On 27 September 2024, Hurricane Helene made landfall on the Florida coast, but the devastation it has left behind has extended far beyond its initial area of impact. With the death toll at nearly 200 people at the time of writing, that number is expected to rise, and those remaining now grapple with the immense cleanup left in the storm's wake.

The buzz saw of a rapidly strengthening Hurricane Helene reaching Category 4 intensity (via Reed Timmer, PhD) 

Landing in the evening near Perry, Florida, Hurricane Helene was a powerful Category 4 storm with sustained winds of 130 mph (209 kph). The low-lying areas around Perry and the nearby coastal towns were particularly vulnerable to the storm surge, which rose to 4.5 meters in some places and inundated homes, businesses, and infrastructure along the coast, causing widespread damage to buildings and utilities. Streets became rivers as floodwaters surged several miles inland, and some areas were reported to have as much as a meter of standing water. The powerful winds not only caused extensive damage along the coast but also extended deep into Florida, toppling trees and power lines and causing widespread damage to buildings in their wake.

One of the most devastating impacts of Helene’s landfall was the storm surge combined with heavy rainfall, which overwhelmed the region’s drainage systems. Roads were impassable, cutting off access to emergency responders and leaving residents stranded. In addition to physical destruction, hundreds of thousands of people lost power across Florida, and the flooding left entire communities isolated. Emergency shelters were quickly filled to capacity, and evacuation orders were issued for low-lying areas well ahead of the storm's landfall. The Florida Panhandle, still recovering from previous hurricanes in recent years, was hit hard again, causing major disruptions to local economies, particularly tourism, agriculture, and fishing industries.

A powerful storm surge in Florida caused by Hurricane Helene (via Nahel Belgherze)

As Helene moved inland, the storm weakened in terms of wind strength, but its most deadly effects were still to come. Areas of North Carolina, especially the western mountainous regions, had experienced a separate weather system in the days leading up to the hurricane, which had already drenched the area after a period of drought, saturating the ground and filling rivers to dangerous levels. This laid the groundwork for disaster, and by the time Helene arrived, there was no room for additional water​.

Massive debris flow travelling at lightning speed in eastern Tennessee (via Reed Timmer, PhD)

The storm moved over the Blue Ridge Mountains, and its interaction with the terrain caused what is known as orographic lift, where moist air is forced upwards by the mountains, resulting in intensified rainfall. This geographical factor, combined with the storm’s moisture-rich remnants, caused areas in Western North Carolina to receive over 30 inches of rain in less than 48 hours. Towns like Asheville, Boone, and Hendersonville saw their rivers swell to dangerous levels. Major highways were submerged, cutting off access to these communities. Landslides became another deadly aspect of the storm, with entire hillsides collapsing onto homes and roads.

The flooding in North Carolina was further complicated by the winds Helene brought with it. The storm’s eastward shift exposed the state to stronger winds, which toppled trees and power lines, exacerbating the flood risks by preventing timely communication and evacuation. In addition, the rain runoff from the mountains flowed into river systems like the French Broad River and the Catawba River, which quickly overflowed, flooding towns and causing massive damage​.

The town of Chimney Rock in North Carolina has been virtually wiped off the map (via Ella Dorsey)

As floodwaters rose, entire neighborhoods were submerged. In Asheville, residents were forced to climb onto their roofs to await rescue. In Boone, the flooding devastated both commercial and residential properties, with homes swept off their foundations and roads completely washed away. Some of the more remote communities, such as those along ridgetops and in deep valleys, remain without power or access to supplies. Communication outages in these areas are slowing emergency response efforts and rescuers' efforts to reach those in need, and the extent of devastation in some towns will take years to recover from. 

Asheville, North Carolina, after Hurricane Helene passed through (via AccuWeather)

In recent years, the rapid intensification of storms like Hurricane Helene has become more common, driven in part by rising sea surface temperatures. Warm waters act as fuel for tropical cyclones and hurricanes, causing them to strengthen more quickly than they have in the past. Scientists have observed that warmer oceans, combined with higher atmospheric moisture levels, are enabling storms to grow in both size and severity at a faster rate. This was visible in the case of Helene, which went from a Category 2 to a Category 4 hurricane in less than 24 hours before making landfall.

A similar setup was seen recently in Queensland, where Cyclone Jasper and Cyclone Kirrily impacted the state in close succession. In both cases, the storms intensified quickly, and heavy rainfall prior to the cyclones had already saturated the ground, priming the area for catastrophic flooding when the storms made landfall. Like Helene, the combination of intense winds, storm surges, and heavy rain led to widespread damage, cutting off communities, flooding homes and businesses, and overwhelming emergency services.

Looking ahead, meteorologists are predicting a season with higher-than-average rainfall across key parts of Australia, including Queensland and New South Wales. With warmer waters continuing to persist in the Pacific and Indian Oceans, the threat of more rapidly intensifying storms is ever-present. This could mean an increased frequency of cyclones and hurricanes, along with more severe flooding, especially in regions already at risk.

Damage in Mareeba Shire after Cyclone Jasper (image via Mareeba Shire Council) 

As the frequency and intensity of storms continue to rise, it's more critical than ever for businesses, insurance companies, and government agencies to be proactive in preparing for upcoming storm seasons. With forecasts pointing to a higher-than-average rainfall season for 2024/25, now is the time to educate yourself about the risks and implement strategies to protect assets, minimise operational downtime, and safeguard communities. One of the key aspects of preparation is accessing reputable, real-time information about potential threats and understanding how to act on it quickly.

By partnering with trusted weather intelligence providers, businesses can ensure they have accurate forecasting and early warnings for approaching storms, helping them plan for disruptions and manage risks. Insurance companies can also benefit from more precise predictions of storm impacts, allowing them to better assess potential claims, reduce fraud, and adjust premiums based on reliable data. Government agencies can also enhance public safety by using advanced weather data to inform emergency response efforts, issue timely evacuation orders, and coordinate recovery efforts efficiently.

At Early Warning Network, we offer a suite of products designed to meet the needs of businesses, insurers, and governments in these critical times:

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Our state-of-the-art flood services help you track and predict water levels with precision, offering early warning alerts that can save lives and property. With detailed, localized data, governments and businesses can make more informed decisions about evacuation plans, resource allocation, and community protection measures.

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