The Tropical Cyclone Intensity Scale (TCIS) is an unofficial scale used to determine how intense a tropical depression, tropical storm, or hurricane is beyond the standard Saffir-Simpson hurricane categories. The Saffir-Simpson scale only factors in wind speed to determine the strength of the storm. While this is a perfectly fine way to categorize storms, sometimes the public does not heed the proper precautions for lower storms like tropical depressions and storms, and even category 1 and 2 hurricanes. Additionally, by assigning numbers to storms instead of broad categories, comparing two storms is easier.
The TCIS factors in not only wind speed, but also pressure, forward movement, physical size, and distance from land. Physical size in this context refers to the distance that tropical-storm-force winds can be felt. Each of these factors is weighted differently, depending on importance to determining intensity.
The scale is measured in Intensity Points (ip) between 0.0 and 12.0, including tenths. For reference, some recent historical storms and their Saffir-Simpson rating, along with their TCIS rating:
Katia 2011 (Cat3): 7.5
Lee 2011 (TS): 5.5
Isaac 2012 (Cat1): 8.1
Harvey 2017 (Cat4): 8.5
The TCIS was created by weather nerd and comedian Geoffrey Gauchet in 2011. Other than his interest in tropical weather and being a software engineer, he has no real qualifications to create this type of scale. As such, it should not be used for emergency planning purposes. This is an unofficial scale and has not been overly tested, nor has it been peer reviewed. The algorithm is tweaked each season. For more information, contact him on twitter at @animatedGeoff. All raw storm data is from the National Hurricane Center.