The Hurricane Severity Index – A destructive potential rating system for tropical cyclones

A larger tropical cyclone can produce a significantly greater storm surge, wider swath of wind damage, greater duration of strong winds, larger area of heavy rainfall and greater wave heights than a smaller tropical cyclone that is otherwise identical. For example, Hurricanes Ivan (2004) and Dennis (2005) were both Category 3 hurricanes with 105 kt maximum sustained winds at landfall near Pensacola, FL. But Ivan was significantly larger and caused $13 billion in damage versus $2.23 billion from Dennis.

The Saffir-Simpson Hurricane Scale (SSHS) has been used to classify Western Hemisphere tropical cyclones that contain hurricane-force winds since 1969. But because the SSHS is based solely on a tropical cyclone's maximum winds, it is not adequate for quantifying the overall destructive potential of a hurricane. In order to better gauge the potential impact of a tropical cyclone, the size of its wind field must also be taken into consideration.

The Hurricane Severity Index (HSI) rates the severity of all types of tropical and subtropical cyclones based on both the intensity and the size of their wind fields. The HSI is a 0 to 50 point scale, allotting up to 25 points for a tropical cyclone's intensity and up to 25 points for wind field size. Points are awarded on an exponential scale, with the majority of points reserved for hurricane force and greater wind fields.

This paper describes the HSI in detail. The authors propose for the HSI to be utilized by the meteorological community as the primary rating system to quantify the destructive potential of tropical cyclones.