"There were more northeasterly winds than usual for the month," Macara said.
"Those are coming from the sub-tropics, so that's delivering more warmer air masses than we'd normally receive in June.
"You contrast that with receiving more southwesterly winds, which are coming from Antarctica."
The second factor was warmer sea surface temperatures around New Zealand, Macara said.
"Our climate is essentially characterised as maritime, which means it's influenced by the sea.
"In this case the warmer than normal surface temperatures have helped to sustain those warmer than normal air temperatures as well."
Other local areas were also warmer than usual in June.
Mt Ruapehu Chateau had an average temperature of 5.5C while Ohakune's was 8.6C - both of which are the second highest mean temperatures ever recorded in June.
The average minimum temperature at Mt Ruapehu/Chateau was 1.9C (fourth highest) and the average maximum temperature was 9C (third highest).
For Ohakune, the average maximum temperature of 13.3C was the highest since records began in 1962.
Macara said the third factor in explaining the warmest June on record was underlying climate change.
"New Zealand's climate is warming - it's warmed one degree over the past 100 years.
"It's expected to continue to do so, and it's shifting our base line to a relatively warmer place. In other words, it's increasing the chance of these above average temperatures occurring."
Warmer temperatures were predicted to continue for the rest of winter, Macara said.
"That's not to say we won't have cold outbreaks, we'll have our frosts and snowfalls, but, generally speaking, the expectation is it will be a warmer than normal winter.
"There is difference between weather and climate.
"Our weather will remain variable and conducive to those frosts and snowfall for a long time to come, but the actual climate - the long-term average of weather - is the thing that's shifting and getting progressively warmer."
