CONTINUATION OF DEVELOPMENT OF A NEW HURRICANE IMPACT SCALE: WCI, THE SHELF WIDTH/SHORELINE CURVATURE INDEX

The Saffir-Simpson Scale (SSS), which is currently used to rank hurricanes, is based solely on each hurricane's maximum sustained wind speed. This is an effective method for comparing hurricane strength in the open ocean, it presents problems with predicting hurricane damage at landfall. Limitations of the SSS led to the development of the Hurricane Impact Scale (HIS), which better reflects the potential for erosion, overwash, and property damage at the coast. The HIS considers storm surge height and storm surge spread, as well as the SSS ranking.

As part of the continued refinement of the HIS, the effects of shelf width and shoreline curvature on storm surge are being quantified. The relationships between shelf width, shoreline curvature, and storm surge are qualitatively straightforward: the wider the shelf and the more deeply embayed the shoreline, the greater the potential storm surge.

Shoreline curvature (Curvature = C/P) is a simple measure of the amount of concavity of a given coastal embayment. It is the chord length (C) of the outer (seaward) opening of the embayment divided by the length of the longest perpendicular (P) drawn from the chord back to the innermost shoreline. That ratio is small for deeply embayed coasts (greater surge potential) and large for gently curved coasts (lower surge potential). The WCI is the ratio of shelf width to shoreline curvature. Simply divide the average shelf width by the C/P value for that embayment. A wide shelf with a deeply embayed coast (small C/P) will have a high WCI indicating a high surge potential. Conversely, a narrow shelf with a straight coast (large C/P) will have a low WCI indicating a low surge potential. The Width/Curvature Index (WCI) ratio provides a numerical value to predict the effects of hurricane storm surge on a specific area. The inclusion of this ratio could allow for the maximum storm surge to be accurately predicted, and allow for better guidance for storm preparedness.