Much of the North Island was forecast to wake to sub-zero temperatures this morning as a blast of cold southern air delivered late-season frosts less than a day after the spring equinox. MetService expected Taumarunui to fall to -4C, Rotorua to -2C and Hamilton and Whakatane to -1C, with parts of Auckland dipping to 3C or 4C on what forecasters picked as the coldest morning of the week.
The equinox fell on Wednesday, the point in the calendar when day and night are roughly equal in length and the season formally tips toward summer. The weather had other ideas. MetService forecaster Chelsea Glue told 1News on Wednesday evening that the North Island would bear the brunt of the cold overnight.
“We’re going for below-zero temperatures for many places in the North Island tonight, frosty conditions,” Glue said. She said the temperatures were “quite cold for this time of year” for the North Island. “Normally [they’re] starting to get a little bit warmer this time of year, but a few late-season frosts are still in the cards for them.”
The mechanism is a familiar spring one. A cold change moved up the country on Wednesday, bringing southerly winds and a colder air mass from the south. Once the rain and cloud cleared away to the north, the skies opened up and the heat escaped. “As the rain and the cloud starts to clear away to the north, we’re left with clear skies and that allows for temperatures to drop overnight,” Glue said.
The South Island was not spared, though its residents are better acclimatised. Christchurch was forecast to reach -2C and Blenheim -1C, and Nelson was expected to fall to 1C, which Glue described as “pretty chilly” for a region that prides itself on sunshine. “They’re probably a little bit more used to the colder temperatures down there, so it’s not quite so unseasonable for them,” she said.
The timing is awkward for orchardists and gardeners. Late September is when blossom is out across much of the country and frost-tender seedlings are going into the ground. “Just when you’re starting to think you’re getting into fruit-growing season, you’ve got to be mindful of these frosts coming in,” Glue said. Anyone with young plants in the ground can check what is safe to plant this month in our NZ Gardener’s Planting Calendar.
Thursday’s frost is the payoff from a week of unsettled weather. MetService meteorologist Dan Corrigan told 1News on Tuesday that a cold change had moved through the lower North Island that morning, bringing colder temperatures and brief rain. “It’s gone through Wellington, it looks like it’s just going through Masterton at the moment,” he said. “That’s bringing significantly colder temperatures and a bit of rain with that, spreading up the North Island throughout today. It’s going to be pretty brief rain, it won’t be lasting long, and that’s quite characteristic of these fast-moving spring weather systems that we often get at this time of year.”
Corrigan put Auckland’s expected Thursday low at just 4C. “Average minimum temperature for a day in late September in Auckland is 10.4, so that’s six degrees below that. It will feel notably cold,” he said. He expected most of the South Island to see frost on Thursday morning, with only Northland and cloud-affected areas such as Wellington likely to escape it. Invercargill was picked for the strongest winds on Tuesday, with gusts of up to 90 kilometres an hour forecast. “Even though it’s going to be chilly in terms of the temperature, it’s also going to be wind-chilly, if you like,” Corrigan said.
Road snowfall warnings were in force across the South Island on Tuesday and Wednesday. Milford Road was under a warning from 10am to 5pm Tuesday, with 2 to 4cm of snow forecast about the tunnel entrance. Crown Range Road faced a warning from 8pm Tuesday to 2am Wednesday, and Lewis Pass from 9pm Tuesday to 4am Wednesday, with 1 to 2cm expected about the summit. The Desert Road in the central North Island was under a warning from 9am to 5pm on Wednesday.
The snow did close a road. NZ Transport Agency Waka Kotahi said the section of State Highway 73 between Springfield and Arthurs Pass Village, including Porters Pass, was closed just before 4am on Wednesday and reopened about 5.20am, according to 1News. An NZTA spokesperson said “winter” driving conditions persisted elsewhere in the South Island, including State Highway 1 between Dunedin and Waitati, and urged motorists to take “extreme care”. Wednesday morning was already cold, with Ashburton the coldest spot at 0C at 7am and Wanaka and Milford Sound sitting at 1C.
The same southwesterly flow produced a rarer sight further north. Photos sent to 1News showed a funnel cloud off the south Taranaki coast near Opunake about 9am on Wednesday. Marama Hohaia saw it forming during the school drop-off. “We watched it for about 30 seconds and it fizzled out again but was very loud then as we were driving home we had real heavy winds,” she said. MetService forecaster Samkelo Magwala said a series of fronts was moving up the country, with a ridge of high pressure over the Tasman Sea creating the southwesterly flow. “There’s that possibility of some form of convective cloud,” Magwala said. “The atmospheric conditions are conducive. There’s cold temperatures aloft, which are more consistent for the formation of such clouds.”
Funnel clouds form when rotating air beneath a convective cloud tightens into a visible spout. They become tornadoes only if they touch the ground, and most, like the Opunake one, dissipate within a minute or two. Cold air aloft over relatively warm sea makes the atmosphere unstable enough for them to form, which is why they tend to show up along the west coast during exactly this kind of spring southwesterly.
The reprieve will be short. Glue said many places would see fine, clear skies on Thursday, although showers would linger in parts of the far south. Corrigan said the next system would move in from the Tasman Sea on Friday. “It won’t be long until the next lot of weather arrives on Friday,” he said. “In springtime, these things tend to move quicker through, so the periods where it’s settled don’t tend to last as long.”
For most of the country that means one sharp, bright, frosty morning and then back to the usual spring churn of fronts and clearances. For growers in the Waikato, Bay of Plenty and central plateau, where the forecast lows were deepest, it is a morning to check the blossom and the seedlings before the sun gets to them.
How cold was it at your place this morning? Did the frost catch your garden or your orchard? Tell us in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
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