Is it time for a Category 6 for super cyclones? No – warnings of floods or storm surges are more useful

• If a Category 5 storm with wind speeds of 250 kilometres per hour is heading for you, you prepare differently than you would for a Category 1 with wind speeds of 65 km/h.
• In a hotter world, cyclones are expected to become less common but more intense when they do form.
• Only one hurricane in the Western Hemisphere has yet gone past the 309 km/h winds the researchers nominate for a Category 6.
• And the whole idea of storm scales, including Australia’s own tropical cyclone scale, is that Category 5 storms are those likely to do catastrophic damage.

What are storm scales for?

• There are several different intensity scales in use.
• Different scales are used in the Australian, North Indian, Southwest Indian, and western North Pacific basins.
• Tropical Cyclone Oswald, a 2013 Category 1 storm, led to heavy rainfall and flooding through Queensland and New South Wales, while the 1992 Category 5 Hurricane Andrew caused catastrophic wind damage – but little rain or storm surge damage when it hit Florida.

So do we really need a Category 6?

• But this is the only one which meets their criteria in the last 40 years, as it was well observed by US aircraft missions.
• The Australian Tropical Cyclone Scale has different thresholds but similar reasoning for a Category 5 storm.
• Based on the understanding that winds at Category 5 and above lead to catastrophic outcomes, it’s hard to see how adding a Category 6 would help the public.
• If a Category 5 means “expect catastrophic consequences”, what would Category 6 mean?

How can we best communicate cyclone threats?

• Scientists came up with tropical cyclone intensity scales as a way to clearly communicate the nature and size of the damage likely to occur.
• Fundamentally, these scales are meant to measure how well our buildings and infrastructure can survive the wind force and also protect us.
• Read more:
  Even weak tropical cyclones have grown more intense worldwide – we tracked 30 years of them using currents

Liz Ritchie-Tyo does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.