Study urges forecasters to adopt new hurricane intensity scale
A proposed “Tropical Cyclone Severity Scale” could do a better job at relaying a storm’s hazards than the current Saffir-Simpson scale
A recent study joins a growing chorus of calls for experts to adopt a new intensity scale to rank the power of hurricanes.
The current Saffir-Simpson Hurricane Wind Scale (SSHWS) only takes into account a storm’s sustained winds.
That’s not enough, experts argue—a hurricane’s flooding rains and storm surge often cause more death and destruction than winds alone.
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Current scale only factors in a storm’s winds
Created in the early 1970s by Herb Saffir and Bob Simpson, the SSHWS grades a hurricane’s maximum sustained winds on a scale from 1 through 5.
Use of the SSHWS is so deeply engrained in coastal culture around the Atlantic Ocean that some residents simply refuse to evacuate unless a storm escalates to a certain category.
But winds are only one component of a storm’s hazards, and its category doesn’t always convey the seriousness of the situation.
Hurricane Katrina was 'only' a Category 3 when it slammed into the Gulf Coast with a catastrophic storm surge. Hurricane Helene significantly weakened as it pushed inland, yet it unleashed historic flooding across western North Carolina.
A new scale designed for multiple hazards
Meteorologists and social scientists have long sought a way to encapsulate a storm’s hazards beyond just its maximum winds. The vast majority of storm-related fatalities are caused by storm surge or flooding rains.
A 2021 paper offered the Tropical Cyclone Severity Scale (TCSS) as a replacement for the current SSHWS. Operating on a familiar 1-to-5 scale, the proposed TCSS would incorporate three major hazards: winds, storm surge, and accumulated rainfall.
The wind component would work exactly the same as the current Saffir-Simpson scale.
Predicted storm surge values account for potentially lethal coastal flooding, with values derived from destructive storms in recent history.
Accumulated rainfall would also play a role, with higher totals representing a greater threat for life-threatening flooding along the path of the system.
The highest category among the three components would constitute the hurricane’s final ranking. A storm that produced 154 km/h winds, a storm surge of 3 metres, and 600 mm of rainfall would qualify as a Category 4, for instance.
Study finds benefits in adopting a new intensity scale
A paper recently published in Nature Scientific Reports found that the proposed TCSS could improve comprehension of a storm’s threats and inform better decisions surrounding preparation and evacuation.
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Researchers offered a detailed survey to more than 4,000 people from Texas to Maine, aiming to understand how residents in coastal regions understand and interpret the threat posed by landfalling storms.
Participants were offered information about hypothetical hurricanes using either the SSHWS or the proposed TCSS and asked how they would prepare for those storms.
“Overall,” the researchers wrote, “our results demonstrate that people make better informed and more appropriate decisions with the TCSS as opposed to the current SSHWS.”
Potential downfalls of a new scale
A new hurricane rating scale could dramatically improve how forecasters communicate the hazards posed by a storm, which could in turn benefit residents in harm’s way.
But switching to a new scale could have plenty of drawbacks, as well.
A multi-faceted scale such as the TCSS may prove confusing for the general public. A larger number of Category 4 or Category 5 storms may result in a crying-wolf effect that meteorologists strive so hard to avoid.
Forecasting both storm surge and accumulated rainfall is complicated. These hazards depend on factors such as a storm’s size, intensity, and track, as well as the affected region’s terrain and coastline.
Any potential replacements for the SSHWS would have to take these issues into consideration.
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