Standardizing hurricane size descriptors for broadcast to the public

The effects of Hurricanes Katrina and Ike have highlighted the importance of the size attribute of hurricanes, together with track and intensity, in constituting the threat to the public. These two large storms, bearing intensity designations of SS3 and SS2 respectively, presented dangers to the public greater than their Saffir-Simpson categories would have indicated, in part, because of the additional dimension of threat posed by their size. Public awareness of storm size as a significant component of the hurricane threat is particularly important because of the contribution of size to surge heights, as well as the connection of the 34-kt wind threshold to evacuation timing and deadlines, both of which proved significant during Hurricane Ike, an extraordinarily large storm by Atlantic standards. The public could benefit from easy to understand, nontechnical, comparative size descriptors that apply specifically to hurricanes and tropical storms occurring in the Atlantic basin.

Storm size is defined for forecasting purposes as either the radius of the gale force winds or the radius of the outermost closed isobar (ROCI). Since the gale force winds are the same as the 34-kt or tropical storm-force winds, descriptions and forecasts pertaining to the 34-kt wind radii for each quadrant of the storm, as found in the official NHC advisories, may be used to convey information about size for both tropical storms and hurricanes.

The concept of wind radii, mathematical by nature, is a technical construct that requires lengthy explanation to be properly understood by nonspecialists. Sufficient time for elaboration is rarely afforded to broadcast meteorologists, except in the context of a real-time hurricane emergency. In addition, the numerical size descriptor may not by itself be particularly meaningful to the nonspecialist, without some preexisting sense of scale as it pertains to Atlantic hurricanes. It might be more beneficial to communicate to the public whether a current storm, given its estimated wind radii, is particularly small or large as storms go, relative to other hurricanes occurring in the Atlantic basin.

This research examines, using data from past NHC advisories, how the bounds of a small, medium, or large storm might be expressed on the basis of the 34-kt wind radii. Official forecaster characterizations about the relative sizes of storms, informally by Atlantic basin standards, are analyzed in the context of the 34-kt wind radii data the forecasters had available when they made their characterizations. Similar statements and estimates made by official forecasters with respect to historical hurricanes are also examined. It is theorized that these past official characterizations might serve as useful guidance in the development of easily understood, standardized storm size descriptors for broadcast to the public.