Experts debate whether higher 'Category 6' cyclone rating is needed amid increasingly volatile storms

February 24, 2018

A Cyclone 5 rating is currently the most severe category for tropical storms.

The recent destructive weather, and predictions that climate change will bring more of it, have started a debate over the way cyclones are classified. 

The most severe tropical storms are rated Category 5, but now it's being suggested a Category 6 should be introduced. 

Although prepared, Fiji proved no match for Cyclone Winston's fury two years ago when its brute force wreaked havoc and claimed 44 lives. 

And despite the highest cyclone classification possible, Winston's 230-kilometre-an-hour winds exceeded its Category 5 cyclone rating.  

That's now fuelling discussion over whether a new Category 6 rating is needed. 

"Given the likelihood that we will continue to see more severe storms in the future that might be something that's worth considering," said James Shaw, Climate Change Minister.

Weather experts agree climate change is creating far more frequent and volatile weather events, but say a cyclone's classification doesn't always determine its behaviour.   

"Even though Fehi was on the scale very low, it had king tides, so it's storm surge was just overwhelming," said Dan Corbett, 1 NEWS meteorologist.  

NIWA chief scientist Chris Brandolino pointed out that weak tropical cyclones such as a Category 1, the lowest on the scale, "can cause a lot of flooding, and cause a lot of damage and a lot of disaster". 

Ex tropical storms Fehi and Gita still packed a punch when they arrived here, despite no longer having a cyclone rating. 

"Yes there was wind damage in Taranaki. But think of all the flooding and slips and the water impacts that occurred from the Tasman region down to Kaikoura. And that was much larger than the wind impacts," Mr Brandolino said. 

Dan Corbett says understanding the weather and its impact is the best way to keep people safe. 

"It's also our job as well, when we're talking about the storms, to drill it down and communicate to people, to sit there and say this is a storm number but it's going to do so much more damage. And that's where people can then understand it better," he said.

The weather is now more than just a numbers game as the world gets to grips with climate change. 

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