With one month to go, New Zealand is on track to record its second successive warmest winter on record, after experiencing its warmest June and July since records began in 1909.
Data from Niwa’s Seven Station temperature series showed the temperature for the past two months was an "extremely high" 1.53degC above the long-term average.
Meteorologist Ben Noll said the previous record was 1.15degC above average for June and July in 2016.
Several factors had contributed to the warmer temperatures.
"Air pressure has been higher than normal in the east so far this winter which has brought more northeasterly winds to New Zealand, bringing warmer air from the sub-tropics.
"Sea temperatures around the coast have also been warmer than average, modifying colder air masses tracking towards New Zealand," Mr Noll said.
The southern hemisphere polar vortex above the Antarctic had been stronger than normal, which had helped keep filaments of frigid air "tucked away" in the Southern Ocean.
Atmospheric patterns had also leaned towards a La Nina-like direction, which tended to produce warmer conditions in the Southwest Pacific.
Middlemarch recorded its equal-highest daily maximum air temperature on July 6 when the mercury hit 18.2degC, and Manapouri Airport recorded its second-highest on July 25 when it reached 16.1degC.
Lauder recorded its second-highest one-day rainfall total since 1924, when 28mm fell on July 6. On the same day, Haast recorded its third-highest since 1943, when 114mm fell.
Nationwide, temperatures were 1.7degC (June) and 1.9degC (July) above average.
Mr Noll said because the temperatures were tracking so far above average, this winter had a firm lead on last year’s figures.
"This is consistent with our expectations. In the background, the long-term tailwind of climate change continues to churn.
"Of the seven warmest Junes and Julys, six have occurred since 2000."
The year to the end of July 2021 was the sixth-warmest on record, he said.
