Introduction to Hurricane Rating Systems
As Tropical Storm Debby grazed the Tampa Bay area last August, many Floridians treated it like any other summer rainstorm: Inflatable floats dotted Bayshore Boulevard, curious onlookers flocked to the beach and drivers plowed through pooling floodwaters. But Debby’s ugly side soon appeared. About a day after the storm passed, the Alafia River swelled to nearly 20 feet, its highest level in seven years. Homes in Lithia and Riverview were inundated with floodwater. All told, the storm claimed 17 lives in the U.S., strengthening to a Category 1 storm at its peak but never becoming a major hurricane.
The Current Saffir-Simpson Scale
Researchers point to Debby as just one recent example of what’s wrong with how tropical cyclone risk is communicated. Forecasters in Tampa Bay warned about possible flash flooding and up to five feet of surge for the coasts, but for the chiseled Floridians who pride themselves on their storm hardiness, one main thing mattered in their decision-making: Debby was just a tropical storm. The National Hurricane Center classifies hurricanes using the 1970s-era Saffir-Simpson Scale, which uses only wind speed as its guiding variable. A Category 1 storm has wind speeds up to 95 mph, a Category 2 up to 110 mph, and so on.
A New Approach: The Tropical Cyclone Severity Scale
But Jennifer Collins believes there is a better way. In 2021, Collins, a hurricane researcher and professor at the University of South Florida’s School of Geosciences, joined a team from the Netherlands to answer an increasingly common question in scientific circles: How can we better inform the public of hurricane risks — and make them safer? Their solution was to build a new hurricane classification scale entirely, one that also accounts for the threats of storm surge and rainfall. The team’s so-called Tropical Cyclone Severity Scale works like this: Predicted windspeed from an encroaching storm is ranked on a scale 1 to 5. So is the forecasted surge height, and the rainfall. Those numbers are then combined to create an overall risk category. Jennifer Collins, a researcher and School of Geosciences at USF professor, is helping develop a new hurricane scale, called the Tropical Cyclone Severity Scale, which incorporates storm surge and rainfall in addition to wind. (Jefferee Woo/TNS/Tampa Bay Times)
How the New Scale Works
Tropical Storm Debby, for instance, would only have a wind speed ranking of 1 on the scale. But the storm’s surge posed a higher threat, and would have been ranked a 2. The threat from Debby’s rainfall was higher still, and would be ranked a 3. Put together under the new scale, Tropical Storm Debby would actually have been a Category 3 storm. “So many times I’ve heard, ‘Well, if it’s a major hurricane, then I’ll start paying attention.’ And that concerns me,” Collins said. “I believe in this scale, and I really believe it has the potential to save lives.” Kurt McAnly, 56, of Riverview, Fla., wades around the backyard of his flooded home on Tuesday, Aug. 6, 2024. McAnly’s home was flooded in the early morning hours of Tuesday, forcing him and his two dogs to evacuate at around 4 a.m. McAnly estimates that water rose about 24-30 inches high in his home that morning as a result of Hurricane Debby. (Dylan Townsend/TNS/Tampa Bay Times)
Research and Findings
Three years after developing the new scale, Collins and her team now have data they say proves the public makes more informed decisions about their safety when using an approach that accounts for both rain and surge. In a peer-reviewed study published this month in Scientific Reports, the researchers interviewed 4,000 people in states along the Gulf and Atlantic coasts, including Florida. Each person received 10 fictional forecasts. Half of those surveyed were given warnings from the current Saffir-Simpson model, and half received warnings from the new Tropical Cyclone Severity Scale. They found that people who used the new system led to “substantially better identification of the main hazard” of a storm, and in turn, helped them make more tailored safety decisions like getting sandbags to fend off flooding or deciding whether to evacuate.
Benefits and Support for the New Scale
Collins argues that one benefit of the new scale is how it uses a category approach that the public already knows. But where the Saffir-Simpson ends at a Category 5, the new system can reach as high as a Category 6 to underscore the combined risks from multiple hazards. An example: Hurricane Ian made landfall over Southwest Florida in September 2022 as a Category 4 storm under the Saffir-Simpson scale. Using the new method, Ian would’ve ranked as a 4 in the wind category, a 4 in rainfall and a 5 in surge. Overall, Ian would’ve been classified as a Category 6 storm, according to an analysis provided by the researchers. Before the study was published, Brian LaMarre, the former meteorologist-in-charge for the National Weather Service in Ruskin, participated in a focus group on the new scale. He thinks it’s a good idea. “Now, does the current scale need to be adjusted? I don’t think it needs to be thrown out,” LaMarre said. “But I think this tropical cyclone severity scale — it’s not proposing to throw it all out.”
Conclusion
The introduction of the Tropical Cyclone Severity Scale offers a promising approach to improving how hurricane risks are communicated to the public. By incorporating storm surge and rainfall into the classification system, individuals can make more informed decisions about their safety. The research supporting this new scale demonstrates its potential to save lives by providing a more comprehensive understanding of the hazards associated with hurricanes. As the scientific community and forecasters continue to evolve in their understanding of hurricane risks, the adoption of the Tropical Cyclone Severity Scale could mark a significant step forward in enhancing public safety during these events.
FAQs
- What is the current hurricane rating system used by the National Hurricane Center?
The current system is the Saffir-Simpson Scale, which categorizes hurricanes based solely on wind speed. - What are the limitations of the Saffir-Simpson Scale?
The scale does not account for storm surge and rainfall, which can be significant hazards associated with hurricanes. - What is the Tropical Cyclone Severity Scale?
The Tropical Cyclone Severity Scale is a new classification system that ranks hurricanes based on wind speed, storm surge, and rainfall, providing a more comprehensive assessment of the risks associated with a hurricane. - How does the Tropical Cyclone Severity Scale work?
The scale ranks each of the three components (wind speed, storm surge, and rainfall) on a scale of 1 to 5 and then combines these rankings to determine an overall risk category. - What are the benefits of the Tropical Cyclone Severity Scale?
The new scale provides a more accurate representation of the hazards associated with a hurricane, allowing individuals to make more informed decisions about their safety. It also uses a category approach that the public is familiar with, making it easier to understand and communicate the risks.
