14 September 2017

It’s Time for a 21st Century Hurricane Scale

Posted by Dan Satterfield

Irma was a monster but the Saffir Simpson scale could not tell how mean she really was. GOES-16 image from U. Wisconsin.

Most folks are familiar with the Saffir Simpson hurricane scale and while it’s very useful, it also has some drawbacks. It’s greatest attribute is that the public understands it, but I’m not alone among meteorologists who think the time has come to replace it. We need a new scale that will better indicate the destructive potential of a tropical cyclone, and there are some good candidates out there.

The main reason we need to change is that the Saffir-Simpson scale is mainly dependant on the wind speed and the associated low pressure at the center of the storm. What it does not take into account is the size of the storm and how far out hurricane force winds extend from the eye. That matters. It matters a lot when you think about how destructive it might be and how much water it can throw around.

It matters a lot when you think about how destructive it might be and how much water it can throw around.

Size matters. Not all Category three hurricanes have the same destruction potential. The HSI index is a good candidate for replacing the old Saffir Simpson scale.


Hurricane Camille, for instance, was a category 5 when it came ashore in Gulfport Mississippi on a hot summer night in August 1969, but it was actually rather tiny compared to most strong hurricanes. Hurricane Allen in 1980 covered most of the Gulf of Mexico and if it had not weakened, it had a much higher potential of destruction. Hurricanes come in various strengths and sizes and we need a scale that takes this into account.

There are already methods that measure hurricanes that you have not heard of. One that is commonly used is the ACE. ACE=Accumulated Cyclone Energy index, and it takes into account the wind speed and duration of the storm. Hurricane Irma had an ACE that all by itself was equal to an average entire hurricane season! It did this because it was very intense and stayed that way for days. It set a record for being a acategory 5 hurricane for so long. That said, ACE too ignores the size of the wind field.

The IKE for Hurricane Katrina.

There is also the IKE or Integrated Kinetic Energy Index. It DOES take into account the wind speed. The IKE depends on how wide an area around the storm is experiencing tropical storm force, 50 knot, and 65-knot winds, and it also gives a Surge Destructive Potential (SDP) that goes from 0 to 6. To consider the entire history of a storm a method of integrating the IKE for the storms entire history has been developed, and you can read about TIKE here.

Lastly, is another scale developed by three meteorologists at Impact Weather in Houston. Their HSI scale appeals to me and you can read the paper here. It is similar to the IKE but uses a points system based on max winds and the size of the wind field. I think this scale has real promise with perhaps a merging of it and the IKE even better.

None of these proposed scales is perfect, but it’s time for some of the top hurricane experts to get together and propose a replacement to Saffir-Simpson. Kerry Emanuel, and Chris Landsea would be my pick to lead the group, as they are both renowned experts on tropical cyclones. The panel should have experts on structural damage and someone from the broadcast meteorology community and the NHC. The new scale should be easy to understand by the public, but based on the kinetic energy of the storm and its potential to be destructive. Factoring in flood potential inland is a whole different problem, but it too should be looked at.

The public needs a better idea of how bad a storm will possibly be and Saffir Simpson is so last century.

Note: The two best books EVER on Hurricanes: