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The Niwa National Climate Centre has put a La Nina alert in place for New Zealand, and is likely to confirm the weather phenomenon later this month.
It means we could be in for another really hot summer, similar to the 2017-18 summer which toppled temperature records.
Centre meteorologist Ben Noll said "historically speaking", La Nina made summers very warm and dry in the lower south and west of the South Island.
The last time New Zealand had a La Nina summer was the summer of 2017-18, which was the hottest on record.
"At this point, I think it’s still a seed to plant — there’s still a few months to sort that plant out — but from a historical perspective, that is what we expect to see during La Nina."
Based on the consensus from international weather models, the probability for La Nina conditions was 77% for October-December — an increase of 20% from last month, he said.
Certainly, for the next three months (October-December), he was very confident the South would be much warmer than average, owing to more northeasterly winds than normal and expected warmer-than-average coastal sea temperatures.
In Southland and inland Otago, temperatures were "very likely" to be above average. Rainfall totals were most likely to be below normal and soil moisture levels and river flows were about equally likely to be below or near normal, he said.
In coastal Otago, temperatures were also "very likely" to be above average. Rainfall totals were equally likely to be near or below normal and soil moisture levels and river flows were most likely to be below normal.