An Intensity Scale for Atlantic Coast Northeast Storms

Abstract

A new classification of extratropical storms, or northeasters, is developed for the middle Atlantic coast. The classification is analogous to the commonly-used Saffir-Simpson Scale for tropical cyclones. Based upon wave hindcasts for Cape Hatteras, North Carolina, 1,347 storms over a 42-year period are grouped into five classes. The classification variable is an index of storm "power," which is storm's duration times the square of maximum significant wave height. Based upon cluster analysis, the following storm classes are produced: CLASS I (weak, power ≤ 771 ft²hr), CLASS II (moderate, 771 < power ≤ 1,760), CLASS III (significant, 1,760 < power ≤ 10,000), CLASS IV (severe, 10,000 < power ≤ 25,000), and CLASS V (extreme, power > 25,000). The response of the coast (e.g., overwash, erosion, and inlet formation) to the average waves and storm surge in each class range from minor for Class I to extreme in Class V. This classification is a useful tool in comparing the relative strength of coastal storms and may have some potential applications in near real-time assessment of a storm's destructive power.