HSI Hurricane Severity Rating explained
One or two addressees have asked me to explain 'hurricane severity index', a measurement we will be making reference to as the season kicks off.
HSI was introduced by two respected US meteorologists Chris Hebert and Bob Weinzapfel in 2006, as an enhanced rating system to more accurately judge the strength and destructive capability of a given storm other than those less scientific scales in use elsewhere at that time. It is slowly becoming adopted by other forecasters. Hebert and Weinzapfel's work was based on the inconsistency of damage caused by hurricanes rated on the basis of wind speeds only.
Hurricane IKE for example devastated the upper Texas coast as a Saffir-Simpson Category 2 hurricane in 2008. However, IKE produced a larger and more extensive storm surge and considerably more damage than did supposedly more powerful cat 3 Hurricane ALICIA in 1983. In fact, IKE's storm surge on Galveston Island was nearly equal to the Cat 4 Galveston hurricane of 1900 as well as the Cat 4 hurricane of 1915, thus demonstrating in their view, that the Saffir-Simpson hurricane scale is not adequate to measure a hurricane's true destructive potential.
Shortly after the 2005 hurricane season, these two experts introduced their new hurricane scale that takes into account both a tropical cyclone's maximum sustained wind as well as the size of its wind field. They named this, rather romantically, the Hurricane Severity Index, or HSI. The HSI is a 50-point scale, with up to 25 points allotted for a tropical cyclone's intensity and up to 25 points allotted for the size of the wind field. The Hurricane Severity Index can be incorporated into a damage prediction model to better estimate a tropical cyclone's true destructive potential in terms of projected loss on the area impacted. In addition, the size component of the Hurricane Severity Index can be used to better estimate potential storm surge for a landfalling tropical cyclone. Personally, until this is proved to be flawed - possible if not probable - I would consider this to be the most accurate storm rating system currently available, without being unduly complicated.
Happy to supply more background reading for the truly determined insomniac or committed dinner party bore.
Do carry on.
Captain Adrian McCourtBack