Tornados to increase in ferocity
Tornados are forecast to increase in ferocity, if not in frequency, a prominent climate scientist says.
Auckland-based Professor Jim Salinger said New Zealand experienced about 30 tornados a year, but most were weak compared with twisters in the United States, which could peak at wind speeds of more than 500kmh.
''There might be a tendency to something stronger [in New Zealand] but compared to North America, they're still tiddlers,'' Salinger said.
Twisters in New Zealand fell between category 0 and 2 on the Fujita scale, or F-scale, with wind speeds between 64kmh and 253kmh.
But as climate change created an ever warmer and wetter planet, New Zealand could have more tornados at the upper end of that bracket, such as Thursday's killer 200kmh-plus Auckland tornado.
''The bottom line is that with a warmer atmosphere, there is more water vapour in the atmosphere, so as it condenses into cloud droplets, more energy will be released providing more energy for storms.
''At the same time any precipitation is heavier. This has been seen in recreations of US tornado seasons,'' Salinger said.
New Zealand's twister danger zone stretched through Northland, Bay of Plenty, Waikato, Taranaki and the west coast of the South Island.
Those areas were prone to moisture-laden clashes of warm and cool winds from the north Tasman Sea and subtropics, the pattern that formed the recipe for a tornado.
Salinger said these conditions would escalate as New Zealand was increasingly at the mercy of energetic westerly storms.
''The future of tornados is unclear ... but indications are that they could be a bit stronger.''