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It’s likely to be a hot, humid, and sticky summer for the northern parts of New Zealand, while a drier south may be the place for Kiwis to plan their Christmas getaways.
Those are the weather flavors we can look forward to for the next three months, says a Niwa meteorologist, with a forecast for above-average air temperatures everywhere.
The agency has also formally confirmed the arrival of a La Niña weather system, and warned of the possibility of another marine heat wave developing, with our coastal waters already unusually warm.
La Niña, an ocean-driven phenomenon that traditionally brings moisture to the north, dryness to the south and heat to most places, could prove the strongest in nearly a decade.
Niwa’s newly released forecast predicted near-normal rainfall levels in the north of the North Island, and near- or lower-than-normal amounts elsewhere.
But that pattern was not expected to emerge immediately: November could be a dry month for much of the country, before more subtropical patterns arrived during the December-January period.
For northern places like Auckland, it could be a humid and muggy holiday period.
“I think now we are sitting in the movie theater and watching the trailers,” forecaster Niwa Ben Noll said of the humidity currently hanging over the country.
“[Humidity] It will definitely be a factor, probably more than normal as we move into summer. If you have air conditioning, you will probably want it for your comfort during those sleepless nights. “
Noll signaled a period of hellish humidity that hit Auckland residents during the record hot summer of 2018, which was fueled in part by a weak La Niña.
“The humidity in Auckland was out of the ordinary, it was like Fiji levels, and it was just oppressive and unwieldy,” he said.
“I’d say we could wait a week or two at some point. It’s going to be a bit of a rough summer for that.”
Where were the best places for the Christmas season?
Since high-pressure systems were more likely to be closer to the South Island in late 2020, Noll hoped the southern regions would be the best option.
“Obviously, that flavor can vary from week to week. But given our climate drivers, the dice are loaded a little more towards dryness in the south and humidity in the north.”
In other parts of the Niwa outlook, soil moisture levels were more likely to be below normal in the north of the North Island and the east of the South Island.
And air pressure was predicted to be higher than normal in the Southeast and lower than normal in Northwest New Zealand, a configuration linked to the Northeast airflow anomalies that were a classic business card of The girl.
The outlook also carries the unusual caution of heat wave marine conditions.
Forecasters have already been closely monitoring warming sea surface temperatures (SST), with some pockets reaching 3 ° C above average.
Noll said that local SSTs had warmed “quite noticeably” since September, with waters north of the North Island just over 1 ° C above average.
“That’s pretty impressive. The most anomalous waters are off the west coast of Auckland, where, for the past seven days, the SSTs have been as warm as 2 ° C above average,” he said.
“And looking further west, as you go further into the Tasman Sea, there are actually pockets of water that have been up to 3 ° C above average.”
Sea temperatures around the South Island had also risen to between 0.5 ° C and 0.8 ° C above average.
“So all areas are at least half a degree above the long-term average for October.”
The 2017-18 La Niña coincided with the strongest marine heat wave ever observed in New Zealand.
It pushed the SST to 1.5 ° C above average, and up to 6 ° C above normal in some places on the west coast, as the beaches filled weeks earlier than usual and the beds of mussels and seaweed Marinas around Southland and Otago suffered cascading losses.
Interestingly, Noll said, our waters were getting warmer now than at this point in 2017.
Along with La Niña, another similarity to three years ago was a positive phase of a key indicator called the Southern Annular Mode (SAM).
A positive SAM had meant weaker than normal westerly winds over the South Island with higher pressures, and fewer cold fronts crossing New Zealand with gusts of cold air.
It also blocked the highs in the east of the country, while less churning in local ocean waters allowed the sea surface to warm.
“For people working in the fisheries and marine sectors, I would say keep a very close eye on the situation; you could even draw on your experiences from late 2017 and early 2018 to get a guide to this potential.”
Another marine heat wave would mark the third in just four years, and these events are expected to get longer, stronger and more frequent under climate change.
Warmer seas were correlated with warmer air on land, leading to hot spells and the most melting of our alpine glaciers, but also a wilder climate.
Agencies have already chosen a slightly more active tropical cyclone season in the New Zealand neighborhood, with the possibility of two systems moving within 550 km of the country.
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