Auckland will be met with stronger but less frequent cyclones in the future, climate scientists say.
As the most powerful Atlantic Ocean storm in recorded history tears a path of destruction across the US state of Florida and neighbouring countries, it begs the question: Could such a storm ever hit New Zealand?
With top sustained winds of 290kmh, Hurricane Irma, which killed at least 22 people in the Caribbean, could inflict a natural disaster causing billions of dollars in damage.
For perspective, the highest recorded winds in Auckland over the weekend were about 109kmh.
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MetService meteorologist Peter Little said Auckland’s narrow position between two seas in the north of the country meant that it, along with Northland, tended to bear the brunt of storms that hit New Zealand.
Cyclones tended to weaken over land so Auckland’s position closer to the top of the country nearer open water meant it faced stronger weather systems than the rest of the country.
A cyclone is a group of thunderstorms rotating around a central point due to planetary spin.
Air swirls in towards the centre in a clockwise direction (in the southern hemisphere) and is expelled out the top.
Hurricanes, typhoons, and tropical cyclones are all the same thing, except with different names for different ocean basins.
There is no evidence of a tropical cyclone ever hitting New Zealand, the MetService said.
Wind gusts of 205kmh were recorded in Auckland at Manukau Heads in 1992.
New Zealand’s windiest place on record was Mt John in Canterbury in 1970 with wind gusts up to 250kmh.
Niwa principal scientist Chris Brandolino said modelling future climates was complicated, but emerging research showed that tropical cyclones could become less frequent but stronger.
“The ones which do form will become more intense,” Brandolino said.
Water would be an increasing threat, from either more destructive storm surge due to rising sea levels or flooding from high levels of rain, he said.
Victoria University climate expert James Renwick said while New Zealand would not be directly affected by tropical cyclones some of New Zealand’s most extreme storms came from ex-tropical cyclones.
These were were tropical cyclones that had left the tropics and re-formed as mid-latitude storms due to strong westerlies and lower sea temperatures.
For example in 1968 the effects of Cyclone Giselle were responsible for sinking the Lyttelton to Wellington ferry the Wahine in Cook Strait, and in 1998 the effects of Cyclone Bola caused heavy flooding across the country.
On average one ex-tropical cyclone approached close enough to cause damage or to affect some part of New Zealand each year, he said.
“Three to four such storms might come close to New Zealand in one year, followed by several years of nothing.”
The expectation was that the numbers of storms would go down over time, he said.
Auckland was as prepared as any city in New Zealand, Renwick said.
A snapshot of Auckland Council’s climate mitigation was released several weeks ago, which included addressing coastal erosion, planting trees, enforced green standards for new buildings, intensifying pest management, and harsher building consents.
Last week Mayor Phil Goff announced Tamaki Drive would be raised by up to half a metre to prevent flooding. The seawall would also be made with a curve to deflect waves.