In Auckland, Saturday was expected to be partly cloudy with showers possible north of Whangaparāoa from the afternoon. MetService has forecast occasional rain for Sunday. Both days were tipped to reach 15C and fall to 7C at the coldest.
Showers were expected to linger about the city on Monday and Tuesday before drying out from Wednesday when it should settle into cloudy conditions.
Sub-zero temps in south
Almost everywhere south of Auckland began the weekend with frosts and mostly clear skies. MetService recorded sub-zero temperatures across the South Island this morning, falling as low as -10.7C at Mount Cook Airport.
St Arnaud dropped to -8C, Twizel to -7.7C, Dunedin Airport fell to -6.5C, Alexandra Airport to -5.2C and Christchurch Airport went to -5.1C, MetService said.
MetService meteorologist Alwyn Bakker said temperatures are colder than usual for this time of year due to a “sudden stratospheric warming” (SSW) event – a rare phenomenon that has only been observed three times in the satellite era in the Southern Hemisphere.
This is combined with a ridge of high pressure clearing the skies overnight.
“So there’s a lot of heat loss happening overnight.”
Bakker urged those travelling to the ski fields to take extra care on the roads, as the lower temperatures will cause ice on the road to stick around for longer.
The National Institute of Water and Atmospheric Research (Niwa) explained the SSW event as an anomaly in wind patterns around Antarctica that usually keeps the harsh polar conditions away from New Zealand.
“Every winter, the polar vortex forms high above Antarctica in the polar stratosphere [the second-lowest layer of Earth’s atmosphere]. This year, the vortex is showing signs of being disturbed,” Niwa said.
“When an SSW occurs, it can help to weaken or displace the polar vortex in the stratosphere, which then filters down onto the tropospheric polar vortex [at the lowest layer of Earth’s atmosphere] and influences our weather patterns.”
Raphael Franks is an Auckland-based reporter who covers breaking news. He joined the Herald as a Te Rito cadet in 2022.
