Rethinking Hurricane Impact: StormGeo’s Hurricane Severity Index

As landfalling hurricanes in recent years have been more intense and wetter, understanding a storm’s true threat has never been more critical. StormGeo’s Hurricane Severity Index (HSI) goes beyond traditional wind-speed metrics to offer a more nuanced assessment of potential damage. By factoring in both wind intensity and storm size, the HSI provides emergency managers, insurers, and businesses both on and offshore with a clearer, more actionable picture of a hurricane’s potential impact. 

Moving Beyond the Saffir-Simpson Scale 

For decades, the Saffir-Simpson Hurricane Wind Scale has been the go-to standard for categorizing hurricanes. While useful, it only accounts for sustained wind speeds, often overlooking other critical factors like storm size and duration. This can lead to underestimating the potential for widespread damage, especially from large, slow-moving systems. 

StormGeo’s Hurricane Severity Index addresses this gap. Developed to provide a more comprehensive view of a storm’s destructive potential, the HSI combines wind intensity with the physical size of the storm. A larger storm will cause more effects from rainfall and wind damage and power outages verses a smaller storm with the same wind intensity.  The result is a 50-point scale that paints a fuller picture of the threat posed—not just to coastal areas, but to entire regions in a storm’s path. 

A Tool for Better Decision-Making 

The HSI is already proving valuable for offshore and onshore customers. By offering a more detailed risk profile, it helps businesses make more informed decisions and to better prepare for operational disruptions.  

“Some of our customers who have locations that are prone to storm surge will use the forecast HSI size as an accelerator of their hurricane response plan, either because their location is only threatened by a severe storm surge threat or they want to get a jump on preparations for a major storm,” says Bob Weinzapfel, Senior Product Manager with StormGeo and co-inventor of the Hurricane Severity Index 20 years ago. 

StormGeo also uses HSI as a tool to compare the latest storm with a past storm that made landfall in the same area so that people better understand how this storm may be different”.  For example, as Hurricane Ian in 2022 was nearing landfall in SW Florida, StormGeo meteorologist Derek Ortt said, “Recent aircraft data indicate that Ian continues to rapidly intensity. Winds have increased to at least 155 mph. Ian is expected to make landfall as an exceptionally dangerous hurricane around Charlotte Harbor. It is slightly stronger than was Hurricane Charley and much larger. Thus, the tidal surge is expected to be significantly higher than was Charley.”  Hurricane Ian was an average sized 150mph storm with hurricane force winds extending 50 mph from its center while Charley was unusually small with hurricane force winds of 25 mph from its center. 

In CPI-adjusted 2025 dollars, Hurricane Ian was responsible for an estimated $119.6 billion in damages, while in 2004 in the same area, Hurricane Charley caused an estimated $26.7 billion in damage.

Real-World Impact 

During recent hurricane seasons, the HSI has been used to track storms like Hurricane Ian and Hurricane Beryl, offering insights that traditional models missed. In both cases, the index highlighted the potential for widespread damage well before landfall, giving businesses more time to prepare. 

As climate patterns shift and economic development and population grows in hurricane-prone areas, tools like the Hurricane Severity Index are becoming essential. They enhance StormGeo’s customers understanding of storm threats and how to optimally react to them—potentially saving lives and reducing their business impacts and economic losses. 

Looking Ahead 

StormGeo is in the middle of a multi-year effort to redefine how hurricane forecasting and we are looking to refine HSI to be a bigger part of the way we communicate storm threats.   As the science of storm prediction evolves, so too does the need for metrics that reflect the full scope of nature’s power. 

While hurricanes threats can be confusing, the Hurricane Severity Index offers a clear lens through which to view—and respond to— storms ahead.