As Hurricane Florence came ashore in North Carolina last week, the drumbeat of forecasts from NOAA’s National Hurricane Center—life-threatening storm surge, catastrophic inland flooding and damaging winds—became a reality. With heavy hearts, meteorologists who tirelessly spent the previous week emphasizing these risks now watched first responders conduct high water rescues, and began to count the lives lost.
This has some questioning the role the Saffir-Simpson wind scale, which ranks hurricanes as category 1–5, plays in risk communication—and whether it’s time to change it or abandon it.
The Saffir-Simpson scale describes the intensity of a hurricane based on its top sustained winds and the damage this can cause. From a communication perspective, it provides a simple way to describe increasing levels of danger. The challenge, however, is that simple doesn’t always tell the whole story.
As Florence neared the coast as a category 4 hurricane, forecasters accurately predicted shifts in wind intensity while continually emphasizing the threats from storm surge, torrential rain and inland flooding threat. As the winds decreased, some people saw this as an invitation to take the threat less seriously. Meteorologists cringed as the tweets came rolling in, along the lines of “It’s only a category 2 storm.”
Although hurricane categories capture the intensity of the winds, they are not meant to convey the intensity of any of the other hurricane risks. Still, despite the weather community emphasizing the catastrophic, life-threatening storm surge and flooding risks, a portion of the public remains focused on category.
Why? Because wind is among the first pieces of information we know. When a hurricane forms over water, forecasters depend on observations from hurricane hunter aircraft, satellites and ocean-based sensors for wind, pressure and humidity data. At the time of formation, the weather community may not immediately know the storm surge impact or the rainfall amounts that may cause flooding. So wind intensity becomes the primary description of a hurricane until additional information becomes available.
And just as forecasters use their first observations to describe the storm initially, humans hold onto to the first piece of information they hear. The phenomenon is known as “anchoring”—and while some people might adjust their risk perception as new and more detailed forecast information about flooding and other threats becomes available, many people stay anchored to the danger of winds alone and, hence, the wind category.
There are historical reasons for this. We once thought that wind speeds and storm surge had a linear relationship: if one hurricane had 20 percent higher winds than another, the surge would be 20 percent higher as well. That made hurricane categories vital to identifying evacuation zones. With advanced research from NOAA laboratories and academic scientists, however, the weather community learned that the relationship between wind and surge is much more complex. This is why NHC developed a storm surge flooding mapand now issues surge watches and warnings where appropriate. Thanks to these advancements, storm surge, not wind categories,provides the basis for evacuation zones, as determined by emergency management teams.
While hurricanes happen every year, they do not always happen to you, and thus, the public may not know the important distinction between wind and surge with respect to categories. As such, this may offer one reason why some people still emphasize them in their decision-making.
What’s more, though, is that wind can play a prominent role in a hurricane’s description for days, especially if it forms in the eastern part of the Atlantic Ocean. Even if all weather communicators stopped using the Saffir-Simpson wind scale, people might still anchor to the wind speeds. Introducing a new scale closer to landfall that incorporates all hurricane risks may help to adjust people's risk, but there will still remain a cognitive bias for some to anchor to the first piece of information, wind.
Despite knowing this cognitive bias, there still exists a desire by some meteorologists and emergency officials to change the scale. Perhaps what is influencing them is that today’s observational technologies are markedly different than when the Saffir-Simpson wind scale was developed in 1971. New observational capabilities, such as advanced satellites, combined with continued physical science research advancements, may unleash the potential to innovate the broader hurricane communication system. Innovation, however, takes time and further research—both in the physical and social sciences.
Like the atmosphere, risk perception is complex. Evacuation decisions even more so. Hurricane categories are one piece of a complex, public and private risk communication structure that influences public decision-making. While categories may play a role, it's not the only aspect of perceiving risk. People must personalize and believe that the risk applies to them, factoring in their past experiences. They must adjust their risk perceptions as new information becomes available. Understanding these components is critical to knowing how to innovate our hurricane communication system. As we continue to understand our atmosphere, so too should we continue to understand the public it impacts. By combining physical and social understandings, only then will we begin to uncover how to improve hurricane communication.