After Hurricane Sandy in 2012 I decided to try to devise an index that would help me better analyze the potential damage caused by tropical cyclones. I developed the Hurricane Wind Intensity Size Index (HWISI). HWISI is based on a 100 point scale. It is designed so that a hurricane with a maximum sustained wind speed of 200 m.p.h. (320 km/h) and is as big as Hurricane Sandy will get 100 points.
There are two components to HWISI. There is a Hurricane Intensity Index (HII) and a Hurricane Size Index (HSI). HWISI is equal to the sum of HII and HSI.
The Hurricane Intensity Index is a function of wind speed and it is scaled so that a hurricane with a maximum sustained wind speed of 200 m.p.h. (320 km/h) gets 50 points.
The Hurricane Size Index is based on the radius of the 64 kt, 50 kt, and 34 kt winds and it takes into account the variation of the wind field in four quadrants. If the hurricane has a wind field of the structure and size of Hurricane Sandy it would get 50 points.
In order to help people understand the meaning of the magnitudes of the indices, I developed categories and descriptors for HII and HSI. The categories and descriptors for HII are based on the Saffir-Simpson Scale with some modifications. The descriptors for HSI were chosen after looking at the way the Storm Prediction Center describes the potential for severe weather and the Centers for Disease Control describes the spatial pattern of diseases.
00 – 08 Minimal
08 – 16 Minor
16 – 20 Serious
20 – 25 Major
25 – 35 Significant
35 – 50 Catastrophic
00 – 10 Localized
10 – 20 Regional
20 – 30 Widespread
30 – 50 Extensive
I calculate these indices for all tropical cyclones over the Atlantic Ocean, Caribbean Sea, Gulf of Mexico and Eastern North Pacific Ocean. I also calculate the indices for tropical cyclones over other ocean basins when it looks like they might have a significant impact on land. The indices are presented on the Current TCs page and in my blog on the home page when appropriate.