After a searing start to 2022, Niwa is forecasting plenty more abnormal warmth this summer – and the possibility of tropical cyclone activity this month.
The agency's extra-hot outlook for the next three months has been put down to a mix of drivers, including La Niña warmth, a record-breaking "marine heatwave" in the north, and the background influence of climate change.
Niwa's just-issued seasonal outlook forecast above-average temperatures across the country, accompanied by warm nights and high humidity.
"I think we'll continue to see those 30C or 30C-plus readings around the country," Niwa meteorologist Ben Noll said.
"While we haven't yet seen temperatures yet cross past 35C and into the late 30s, the exceptional thing to me is there just hasn't been any real break in the heat. So, it's been more about the duration of the heat than those anomalous values."
But that didn't mean the mercury wouldn't soar to uncomfortable heights over the next two months – particularly during periods next month when we could swelter in westerly winds and hot air direct from Australia.
Unfortunately for those hoping for respite, subtropical northeasterly winds and a lack of southerly fronts could continue to make cooler days a rare occurrence.
"The prevailing flow has really been from the northeast, so when you have a real lack of days with southerly winds, the chances of having cooler than average days becomes very, very unlikely," Noll said.
Eastern regions on both islands could expect near-normal amounts of rainfall - with either near or below normal levels elsewhere – while extended periods of higher-than-normal air pressure could drive long dry spells, especially in central and western areas.
That flavour was consistent with La Niña, the ocean-driven climate system that's been meddling with our weather since spring, and which is set to stay at the wheel for the medium-term at least.
"As La Niña has effectively altered the circulation patterns in the Pacific, that's meant more high pressure sitting southeast and southwest of the country, and at times, lower pressure leaning on northern and eastern parts of the North Island," Noll said.
"This set-up has enabled those warm, subtropical winds that we've been experiencing."
The system was also somewhat behind widespread warmth in our coastal waters, where sea temperatures have been running at between 1.6C and 2.5C above average.
In the northern North Island, those temperatures even exceeded that of a record "marine heatwave" that unfolded over our hottest-ever summer of 2017-18, while conditions around the west and east of the island have at least matched those of the dramatic event.
With higher pressure to the east of the country, and the Southern Annular Mode – an indicator of storminess in the Southern Ocean – having been overwhelmingly in a "positive" phase, a lack of strong, ocean-churning winds had allowed warmth to build at the sea surface.
This only added to the heat on land, as shown in blistering hot weather amid the year's opening week.
"And, as we know, there's a climate-change influence embedded in this picture, particularly with the expansion of that subtropical high-pressure belt," Noll said.
"It's all meant that, here we are once again, moving into a new year and already starting to worry about abnormally dry conditions in many regions.
"Despite a wet start to the season in many regions, that weather has really faded off, and we've reached more than 20 consecutive dry days in Auckland."
While warmer oceans meant warmer days, these conditions offered fuel for tropical cyclones, and activity was expected in the tropics to the north of New Zealand later this month.
Around one ex-tropical cyclone veered within 550km of the country each season, and this year, Niwa was forecasting an elevated risk.
Along with that, marine heatwaves could load up low-pressure storms with more moisture – an effect just seen during what was the insurance industry's costliest year for flood and storm damage claims.