Seasonal Climate Outlook December 2025 – February 2026. Image / Earth Sciences New Zealand
Many Kiwis are in for a sweltering, dry start to summer, ahead of a dramatic shift that threatens to bring a wet end to the season for the upper north.
The Earth Sciences New Zealand Seasonal Climate Outlook for December 2025 – February 2026 has revealed what summer may have in store.
Earth Sciences NZ’s principal scientist Chris Brandolino told the Herald this summer will have “two personalities”.
“The summer will certainly unfold a bit differently across the country,” Brandolino said.
He said for the upper North Island, the next few days of summer will be active, with heavy downpours and “nasty thunderstorms”, before conditions take a very different turn.
Once the next few days of wild weather move through, we’re likely to see a transition starting as early as the latter part of this week.
“There will be a distinct theme of less than usual [rain] or drier than usual conditions for much of the country, and that does include the upper North Island.”
Brandolino said the theme will likely be persistent for much of the month and might impact the very start of the new year.
There will also be a continuation of warmer-than-average temperatures, particularly for the western and upper North Island and the top of the South.
“Before we go past December, the lower South Island, so places like Southland and maybe even parts of Otago ... I don’t think it’ll be drier than usual for December.
“There’s likely to be more rain down there, and in some parts it could be even a bit wetter than usual,” he said.
He said there is a concern that in some areas of the country, dryness could develop very quickly.
“I think the main thing to also consider is that some areas last summer had dryness and even drought, and that was the interior and western part of the North Island.”
He said some areas already have “unusually dry” soils for this time of year.
“There will be rain today and tomorrow, but it won’t be enough to turn things around completely. Because those areas are currently dry, they may have kind of a head start to that dubious dryness race,” Brandolino said.
Brandolino said as we move into January, there will be another pivot away from the dry December conditions.
“I think the challenge is trying to identify when we’re going to find this new storyline kind of emerging.”
He said in the second half of summer, wind patterns are likely to change, which will signal the start of the shift.
“We’re likely to see air flows that are more congruent or more akin to La Nina.”
Brandolino said when the winds become more regularly from the east to northeast, a change in the rainfall pattern will be noticeable.
“Places like Auckland and Coromandel and Northland and the Bay of Plenty, they’re likely going to see a transition to increased chances of rainfall and potentially heavy rainfall events because our air flows will be changing,” he said.
Meanwhile, Brandolino said areas across the western and lower North Island, as well as the western and lower South Island, are unlikely to experience the same change to wetter conditions.
Brandolino said a “marine heatwave” is currently impacting New Zealand’s ocean surface temperatures.
This is causing warmer air temperatures and more humidity, which has put water vapour in the air. This vapour is fuel for heavy rain.
“We’re seeing ocean temperatures of 20-21C around our coastal waters. That is very warm. That is exceptionally warm.
“That is going to have an upward influence on our air temperatures.”
He said this would be especially true for the North Island, in places like Bay of Plenty, Coromandel, Auckland, Northland and Waikato.
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