News media · Science

¡Hola! Buenos días del Ciclón Hola! Or maybe not.

In recent years, the media has gleefully embraced tropical cyclone categories, telling us, for example, that Cyclone Gita, which reached Tonga on February 12 was “Category 4,” the same intensity claimed for the meandering Cyclone Hola, which the media tell us will wreck New Zealand’s Northland,  Coromandel and East Cape today.

Further, we’re often told, many of these storms are almost as big as the Category 5 Hurricane Harvey, which affected Texas and Louisiana last August (a cyclone, hurricane and typhoon are simply different terms for the same kind of tropical storm, depending where they are).

Until relatively recently, they were simply cyclones, when they were cyclones. Or just storms, when they were just storms.

It’s time to hang on a minute. For a start, Hola is so weak it’s no longer a cyclone by any definition, whatever the media are frantically telling us. It is not now even a particularly big storm, as storms go. MetService, the voice of reason, says it will be a “one-day wonder,” but if you find that at all in a news story, it will be buried at the end.

Most importantly, New Zealand forecasters use a completely different category-system than the US. What we call Category 1 and 2 cyclones are not even Category 1 in the US; their Category 1 is our Category 3. Our Category 4 is their Category 2, and so on. The only similarity is that 5 is the top category in both, and we get to 5 well before the American category does.

We use Australia’s Bureau of Meteorology Scale, which (to the media at least) makes our cyclones appear bigger than the same-digit category used under the American Saffir-Simpson Scale. Look at the chart below  this article, or read more about it on the Bureau of Meteorology Tropical Cyclone FAQ.

And stop worrying. Such storms are not becoming more frequent, anywhere. It is just the media coverage of them becoming noisier and more doom-laden. Harvey was the first major hurricane to make landfall in the US since Katrina and Wilma of 2005 — an 11-year gap — but you would never have learned that from the panic-driven media.

New Zealand has had just two real cyclones in the past half century — Bola in 1989 and Giselle in 1968. Bola mainly affected East Cape north of Gisborne. Giselle was the biggest storm by far  experienced in New Zealand’s continuously recorded history, which goes back to a little before 1800. Giselle  did enormous damage along most of the length of the country and sank the inter-island ferry TEV Wahine with the loss of 52 lives. But the way every tiny storm gets reported now, you’d think they’ve never been worse and that this week’s quite normal storm is always worse than last week’s.  And that is nonsense.

cyclone category scale

Chart: Bureau of Meteorology, Australia.