Hurricane Irma has unleashed her fury across the Caribbean and the south-eastern US. She’s been the second major hurricane to barrel into the US mainland in recent weeks, and with Hurricane Jose following hot on her heels, 2017 is shaping up to be one of the busiest hurricane seasons for at least a decade.

The strength and intensity of Irma – she sustained wind speeds of 185mph for a record breaking 35 hours – has taken everyone by surprise, and some have raised the question of whether a new category is needed, to describe “super-hurricanes” like Irma.

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The Saffir-Simpson hurricane wind scale is based on hurricane wind-speed, with anything over 157mph being given a category 5 – the highest rank on the scale. When it was developed, more than four decades ago, super-hurricanes like Irma were exceedingly rare. But since then oceans have warmed, and models suggest that the probability of more intense hurricanes is likely to rise (for every degree of warming in tropical seas hurricane wind-speeds increase by an average of 10mph), though the overall number of tropical storms is expected to fall.

So from a measurements perspective adding a category 6 (winds over 175mph) seems reasonable, though this extra category tells us little about the risk associated with these winds; any hurricane of category 5 and over is going to flatten most things. Instead, a revamp of the hurricane rating system might make more sense. The National Center for Atmospheric Research’s hurricane severity scale includes such risk factors as whether the hurricane is likely to stall in one place (as Harvey did to devastating effect).

Kate Ravilious @katerav