Summer’s here — with warmth and a storm
Forecasters are picking a warmer summer than usual for New Zealand — with a few twists in the mix. Jamie Morton looks at three big numbers that tell the story
The fine weather accompanying the first official days of summer will remain for a couple of days yet and temperatures are expected to soar on Wednesday.
However “one of the larger storms of the year” is to move on to the country from today.
Napier overthrew Rarotonga as a sunseeker’s dream yesterday, reaching a scorching 28.8C at the airport, compared to Raro’s 27.5C.
The ridge over the country moves away today and northerlies will pick up ahead of an approaching front.
Kaikoura was the hottest place in the South Island yesterday, as the mercury soared to 28.6C. Hastings also tipped 28C, MetService meteorologist Tui McInnes said.
Today and tomorrow are expected to remain fine and sunny, with the heat sticking around tonight.
Aucklanders will slumber in a minimum of 18C, 17C is on the cards for Christchurch and 16C in Wellington.
But tonight will also see a large area of low pressure developing in the Southern Ocean, creating a large storm that will span thousands of kilometres and brush New Zealand and southeastern Australia.
WeatherWatch has described it as “one of the larger storms in New Zealand this year”.
The West Coast will take the brunt of the heavy rain, and slips, flooding and road closures are possible over the next seven days, WeatherWatch reported.
The wind will be fiercest in the Canterbury high country, and Wellington will have strong winds for much of the week, McInnes said. A combination of wind and rain was likely to hit most of the country.
“Overall, you’re more than likely to have some wet weather and some windy weather at some point.”
Auckland will get a warm week, with the temperature reaching as high as 26C tomorrow but Christchurch fares the best out of three major cities weather-wise this week.
Mid-week is expected to be a high point for the temperatures, which will soar over 25C in Napier, Hastings, Timaru, Oamaru and Dunedin.
40%
Niwa gives a 40 per cent chance of above average temperatures this summer — and 35 per cent for near average ones.
Put simply: summer is likely to be another scorcher, with little probability of a cooler season.
The agency projected that all regions would get temperatures sitting on the hotter side of normal, except the South Island’s West Coast, which was just as likely to get average heat.
As far as Niwa meteorologist Ben Noll was concerned, summer kicked off a month early, when the westerly winds and extra air was dragged across from bushfire-ravaged eastern Australia.
“We’ve had a lot of northwesterly flows pulling hot air across the Tasman Sea from Australia, which has been baking over recent years amid ongoing drought,” he said.
“So each time we get this kind of flow — which is just what we’re expecting for the first half of the season — we’re going to keep getting those warm masses from Australia.
“That means that across the North Island — and especially in the east of the South Island — it’s going to get quite toasty.”
Meteorologists have pointed to the fires across the Tasman for lifting temperatures in many parts of New Zealand to 8C to 10C above what normally would have been recorded.
Last week, the pre-summer swelter also drove down soil moisture levels across the upper North Island, as well as in Marlborough, Tasman and Westland.
Niwa’s latest monitoring showed the driest areas for this time of year were coastal Wairarapa, eastern
Marlborough and inland southern Canterbury.
In all, the month was expected to finish somewhere in the top five hottest Novembers on record.
0.78C
Forecasters are closely watching another important driver of summer heat — warmed-up sea surfaces.
Throughout November, sea surface temperatures (SSTs) climbed to 0.78C above normal off the east coast of the South Island, and 0.39C above normal around the north of the country.
“In the last week of November, especially, the southwest Pacific has really started to cook, which is not surprising given the air flows we’ve had coming off the Australia,” Noll said.
That also signalled the resumption of a 32-month pattern of above average SSTs only interrupted by a rare polar event in spring that hauled them back closer to historically normal levels.
Niwa predicted local SSTs would remain on the higher side throughout the season, which would have its own impact.
Not only did warmer seas create positive feedback effects that cranked land temperatures even higher, they could also modify cooler weather systems heading across water towards the country.
Noll pointed out warmer oceans were big factors in last summer becoming New Zealand’s third hottest — and the summer before that proving the warmest ever.
Both came with “marine heatwaves” that drove the melting of glaciers, pushed warm water fish south and put the winegrowing season several weeks ahead of schedule.
Could a third marine heatwave engulf the country?
“I wouldn’t rule it out — and to be honest I wouldn’t be totally shocked if it did happen, either.”
70%
Further out in the equatorial Pacific, oceans were expected to sit in an ENSO-neutral state, meaning in neither La Nina or El Nino, for the next three months at least.
But Noll still predicted summer would come with a hint of La Ninalike conditions, especially in the rainfall stakes.
Niwa projected rainfall levels to hover around near normal for most of the country, with the west of the South
Island, just as likely to get a higher dose, again proving the exception.
Beyond that headline prediction was a more complex picture.
“Early in the season, we’ll see lots of westerlies, which means those dry areas — that’s from Hawke’s Bay down to Wairarapa, along with other places like Bay of Plenty and Northland — will continue that way,” Noll said.
“In the South Island, it’s going to be quite a different story.
“It’ll be stormy in the west as we go through December, with several rounds of heavy rainfall.”
Other regions to the west, Tasman, Taranaki and Wellington included, could get some decent fronts bringing downpours as they sucked up moisture from a balmier Tasman Sea.
But halfway through the season, the pattern could reverse, bringing rain to drier areas and drier weather to wet areas.
“The upshot is, if you’re going camping this summer, you’re best to do it early in the eastern parts of the country or leave it until later if you’re going in a western area.” Why the flip?
At mid-summer, the specific climate driver that’s been influencing our weather since October — something called the Indian Ocean Dipole, or IOD — could switch places with another.
Having been fixed in a near-record positive phase, the IOD has helped create the unusual dryness that stoked Australia’s fire danger.
“As the IOD fades, it will possibly give way to the tropical western Pacific becoming a bit of a climate driver, overall giving us more of a La Nina-like flavour and encouraging more easterly or northeasterly quarter winds,” Noll said. “But that will all depend on how quickly the IOD fades.”
The final year of the decade was on track to finish New Zealand’s third hottest on record. “I sound like a broken record here, but it’s just more of the same that we’ve been dealing with for several years.”
Five of the past six years have been among the country’s warmest.
“Hotter temperatures sound good for holidaymakers, but there is a much more important factor to consider and that’s the warming planet that we live on.”