A University of South Florida professor is leading a call to revise the way hurricanes are classified, arguing that the current system does not adequately warn the public about dangers beyond wind speed.
Jennifer Collins, a hurricane researcher and professor in USF’s School of Geosciences, co-authored a new paper published in Scientific Reports. The paper proposes replacing the Saffir-Simpson Hurricane Wind Scale (SSHWS), which rates storms solely by wind speed, with a new Tropical Cyclone Severity Scale (TCSS) that also considers storm surge and rainfall.
“Frequently, people use the storm’s category to decide whether to evacuate,” Collins said. “That’s incredibly dangerous because if they hear it’s only a tropical storm or Category 1, too often no alarm bells go off, and they see no cause for concern.”
The research points to hurricanes Katrina and Florence as examples where low wind categories masked significant risks from flooding. In 2005, Hurricane Katrina was listed as Category 3 based on wind speed; however, most fatalities and damage resulted from storm surge and rainfall. Similarly, Hurricane Florence made landfall as a Category 1 in 2018 but caused deadly flooding.
A study by Edward Rappaport in 2014 found that while wind accounts for just 8% of hurricane-related deaths, storm surge causes nearly half and rainfall over a quarter.
“There have been too many instances of incredible loss of life and destruction because a low category number on the SSHWS, or even if it’s listed as a tropical storm, did not match the danger of the storm,” Collins said. “Based on our research, we now know that people are more likely to evacuate if they understand the dangers from rainfall and storm surge in addition to wind.”
The TCSS would assign separate ratings for wind, rain and storm surge on a scale from one to five. The overall category could reach six if multiple hazards are extreme. For example, if two hazards rate at three or higher while another is four or five, the final score increases accordingly.
To test how this new scale might affect public response during hurricanes threatening Gulf and East Coast communities—areas frequently impacted by these storms—Collins’ team surveyed 4,000 residents online using both scales across ten fictional scenarios. Participants who received information via TCSS were better able to identify main hazards and showed greater willingness to evacuate when non-wind threats were highlighted.
“The higher category is important,” Collins said. “According to my evacuation research, many people base their decision to evacuate on that number, not just on the details of the hazard.”
The National Hurricane Center adopted its current version of SSHWS in 2012 after removing pressure and surge components from earlier versions used since 1971.
“Without satisfactory and complete information, individuals are likely to miscalculate their personal risk or even be moved to inaction,” according to Collins’ paper.
Collins has studied evacuation behavior during several recent Florida hurricanes including Matthew (2016), Irma (2017), Ian (2022), Helene (2024) and Milton (2024). She collaborated with Nadia Bloemendaal at University of Amsterdam along with Jantse Mol from Amsterdam and Hans de & Dianna Amasino from Tilburg University; together they developed TCSS starting in 2021 before testing its effectiveness further.
Some experts support this approach. Brad Millikin of Global Support and Development stated: “The TCSS more accurately reflects the overall hazards associated with storms, with a sharp focus on ‘weaker’ storms that might not be significant wind events but could still devastate a community based on storm surge or total rainfall… Accuracy is paramount because it leads to better decision-making.”
Collins plans next steps presenting her findings at the National Hurricane Center: “Change is hard for any institution that’s been doing the same thing for years,” she said. “But I’m fairly optimistic that now is the time. We now know many people make decisions based on the category messaging so we need to ensure that we are communicating with a scale which is more realistic of severity… particularly from storm surge and rainfall flooding…”
