CULLOWHEE -- As frequent viewers of The Weather Channel during the late summer and early fall can tell you, meteorologists regularly use the Saffir-Simpson scale to predict the destructive impact of hurricanes spinning toward the coastline.
But as residents of eastern North Carolina can tell you, despite its widespread use, the Saffir-Simpson scale is not the most reliable way to gauge the damage potential of a looming hurricane once it makes landfall.
That's why nationally known hurricane researchers Rob Young of Western Carolina University and David M. Bush of State University of West Georgia are calling for the implementation of a new scale that would forecast with greater detail what will happen when storms move on shore.
The Saffir-Simpson scale -- which ranks hurricanes as category one to five depending upon barometric pressure, wind speed and storm surge -- is a satisfactory way to describe the absolute strength of a hurricane in the open ocean, said Young, assistant professor of geology at WCU. "The existing scale is less satisfactory in describing the effect of a hurricane on the shore during landfall, however. The same storm in a different coastal setting could have a very different impact."
Young and Bush have worked for 12 years conducting reconnaissance work at hurricane impact areas along the East Coast and the Caribbean, funded by the Federal Emergency Management Agency and, most recently, the Public Entity Risk Institute. They point to recent hurricanes Bertha and Fran (1996), Bonnie (1998), and Dennis and Floyd (1999) as evidence of the need for a new scale.
"The same section of North Carolina coast experienced five significant storms within three years. All five storms were very similar in wind speed, but the effects on the coast were quite different," Young said. "We believe a new hurricane impact scale will allow more accurate prediction of possible storm impacts and better comparisons of coastal impacts in other hurricanes."
The actual impacts of any given hurricane on the coast will vary, depending on several geologic and meteorological factors, including wind speed, radius of maximum winds, forward speed of the storm center, track of the storm relative to the shoreline, storm duration, onshore topography, underlying island geology, and recent storm history, Young said. It's not just the characteristics of the storm itself, he said, but also the characteristics of the coastline where the storm makes landfall.
"Another way to look at it is that every hurricane is different. Each has its own personality," Young said. "The Saffir-Simpson scale doesn't take that into account. It's too rigid. We think the Hurricane Impact Scale will consider and predict the impacts of hurricanes as individuals."
The new Hurricane Impact Scale proposed by Young and Bush builds upon the Saffir-Simpson scale to provide a larger range of categories than the five within the existing scale. Criteria to be considered for the new scale, in addition to Saffir-Simpson ranking, are maximum elevation of the storm surge, and storm surge spread (how large an area would be impacted by higher water level). Storms would earn up to five points in each of three factors, for a minimum rating of three and a maximum rating of 15.
Young gave some examples of how the proposed scale would work. Under the Saffir-Simpson scale, both hurricanes Andrew (1992) and Hugo (1989) were rated category four storms, based on wind speed. Under the proposed Hurricane Impact Scale, however, Andrew would have earned a rating of eight, compared to a rating of 12 for Hugo. Both storms earned the same point values based on wind speed and height of storm surge; Hugo, however, had a much greater storm surge spread and would have earned the maximum five points for that factor.
Hurricane Opal (1995) was rated only a category three storm on the Saffir-Simpson scale, but the hurricane's incredible storm surge, which was very high and widespread, bumps it up to a rating of 11 on the proposed new scale. That would leave Opal with a higher rating than Andrew, which is generally considered a more devastating storm because of its strong winds and the extremely high cost of property damage it caused upon landfall at a very heavily populated area of South Florida.
Young and Bush were scheduled to present their scale at the national meeting of the Geological Society of America in Reno, Nev., on Wednesday, Nov. 15. They also will offer their proposal in spring 2001 at the National Hurricane Conference.