It strikes me as a relative outsider that the US needs another metric to describe the power of a hurricane describing the possible future outcome not the current windspeed.

Perhaps its current energy impulse measured in Terawatts, although that is a bit opaque for many people. I doubt the US would warm to the use of 'Hiroshimas' as used in the UK to describe lots of energy.

I notice the news uses Katrina as a yardstick on occasion i.e. 'this hurricane will be less powerful than hurricane Katrina but will last longer' so perhaps that could be used as a reference 'the hurricane will make landfall tomorrow with 70% the destruction of a "Kat".

Perhaps not.