"That figure puts Whanganui in the 'well above average' category," Carrier said.
"Generally speaking, the warming trend isn't just a winter phenomenon, it's all seasons of the year.
"Not only has it been a while since we've had a season that's been cooler than normal, it's been a long time since we've had a single month that was cooler than normal.
"In fact, I believe the last month we had in New Zealand that was colder than average was January 2017."
Overall, New Zealand experienced its warmest winter ever, with a nationwide average temperature of 9.7C.
The minimum air temperature in Whanganui on June 27 was 14.2C, the equal-second highest since 1972.
Elsewhere, Ohakune's mean air temperature for winter was 7.3C and its mean maximum air temperature was 12.4C, both the highest on record.
On June 14, the town recorded a daily maximum air temperature of 19C, also the highest since records began in 1962.
Mt Ruapehu (Chateau) recorded 93mm of rain on July 17, the third highest single day rainfall total since 2000.
Carrier said the last time the country had back-to-back record breaking winters was in 1970 and 1971, and atmospheric conditions during all four winters were very similar.
"They were coming off La Niña from the previous summers, there were a lot of northerly winds, and there were warmer sea temperatures than normal.
"The background influence of climate change in the past 50 years has meant our last two winters were quite a bit warmer than the early 70s, in fact the winter of 1971 was 0.75C cooler than the winter of 2021."
Climate change was "certainly a reality", and would increase over the ensuing decades, but that didn't mean every winter moving forward would be warmer than the one before it, Carrier said.
"Not every season will be record breaking.
"The general trend is upward, there's no doubt about it, but there will still be variation in there."
