This article from Stuff reporting NIWA-talk mentions “A persistent lack of southerlies had a profound impact on the monthly temperatures.”
Or you could say northerly winds brought a flow of warm tropical air over the New Zealand region during June – as shown by this BoM map.
The NZ Herald says – The winter of our content: Warmest-ever June – which mentions June was between 1.8C and 1.9C above normal just beating 2003 which was +1.8C – When global datsets update we can check what they record for June. The NIWA NZ series is heavily adjusted to a warmer trend – explained by Bob Dedekind.
They did have a few sub tropical lows drop down from the coral sea in JUNE. Common in summer but not sure about how common this is in winter. There have been a few tropical dips off the coast of WA as well in June .The sub tropical jet has been anomolusly south as well and sub polar jet contracted well south and very weak.
I thought NZ was having a ripper’ snow season last time l checked. Maybe its the north island that has been much warmer?