Hurricane Helene: Rise to a Monster Storm

The Southeastern United States is currently dealing with the aftermath of Hurricane Helene, a formidable storm that first struck Florida on Thursday, subsequently carving a destructive path up to Tennessee. This storm has resulted in over 100 fatalities, with hundreds more individuals still unaccounted for. Millions of people are experiencing power outages. In Asheville, North Carolina, one of the most severely affected areas, residents are reportedly facing challenges in accessing food, water, and cellphone service. The full extent of the storm’s impact remains unknown as search and rescue operations continue and scientists work to finalize data on the storm’s power.

Hurricane Helene’s devastation can be attributed to its unusual size, intensity, and speed, creating ideal conditions for a supercharged storm. John Knox, a distinguished teaching professor and undergraduate coordinator of the Atmospheric Sciences Program at the University of Georgia, noted, “Everything that we say a hurricane can do, Helene did do.”

Forecasters had already issued warnings about the storm’s unusual size while it was still in the Gulf of Mexico, describing it as “unusually large.” At its peak, the storm’s tropical storm-force winds extended nearly 350 miles from its center, placing Helene in the 90th percentile for storm size, according to the National Hurricane Center. This vast reach meant that the effects of wind, storm surge, and heavy rainfall were felt over an unusually large area.

The storm’s intensity was also significant. Large storm systems do not typically develop a small inner core that facilitates rapid strengthening, but Helene managed to form a relatively small eye and rapidly intensify. This term describes storms whose sustained wind speeds increase by at least 30 knots (approximately 35 miles per hour) within a 24-hour period.

Upon making landfall, Helene’s winds reached 140 miles per hour, categorizing it as a major storm and placing it as a Category 4 on the Saffir-Simpson hurricane scale. The storm hit Florida’s Big Bend region with a storm surge, inundating the coastline with up to 15 feet of seawater. The gentle incline of the underwater topography off Florida’s west coast facilitated the formation of a higher wall of water, with the storm’s size causing the surge to flood a broader area.

Helene also brought heavy rainfall, leading to historic flooding in western North Carolina. At the Asheville airport, close to 14 inches of rain were recorded over three days. The highest preliminary total, recorded in Busick, North Carolina, exceeded 31 inches of rain.

Daniel Brown, branch chief of the hurricane specialist unit at the National Hurricane Center, described the event as catastrophic, particularly for the southern Appalachians, which experienced tremendous rainfall and flooding. However, he cautioned that it is too early to compare Helene with other storms, as damage and fatality reports are still incoming.

Furthermore, Helene’s forward speed was notable, moving between 20 to 30 miles per hour compared to the typical 10 to 15 miles per hour for Gulf of Mexico storms. This speed allowed it to retain more strength as it moved inland, resulting in greater impacts felt much farther from the coast. Climate scientist Karthik Balaguru suggested that inland communities were more exposed to the storm’s hazards due to their lack of experience in hurricane preparedness compared to coastal areas.

Climate change is influencing the dynamics of storms like Helene, with rising global temperatures creating conditions conducive to more intense storms that can rapidly gain strength and retain power onshore. Helene developed amid high sea surface temperatures in the Caribbean Sea and the Gulf of Mexico, with waters along its path reaching up to 31 degrees Celsius (87.8 degrees Fahrenheit). This provided ample fuel for the storm. The increased capacity of the atmosphere to hold moisture due to greenhouse gas emissions from fossil fuels also contributed to more severe downpours.

Further research is required to determine the specific role of climate change in Hurricane Helene. Balaguru likened the effect of climate change to a weakened immune system, noting that it increases the likelihood of severe storms. Knox summarized the situation by stating, “The storm started big, which was bad, it went over hot water, which was bad, it hit a place that is prone to high storm surge, and then it accelerated and went into populated areas and took wind and rainwater to those populated areas. You don’t want to see much worse.”

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