June this year was the warmest on record at Niwa's most important measuring sites.
New Zealand's Seven Station Series recorded the warmest June on record, with an average of 10.3 degrees Celsius.
That series was derived from seven locations: Auckland, Masterton, Wellington, Hokitika, Nelson, Lincoln near Christchurch and Dunedin.
The month had been "exceptionally warm" with just about all of New Zealand reporting temperatures in the above normal, or well above normal range, Niwa said.
Above normal temperatures are 0.51C to 1.20C above average, well above normal is more than 1.20C above average.
"Perhaps most impressive is how wide-reaching and sustained the warmth was during June," Niwa said.
The Seven Stations average surpassed the previous record for warmest June, 2003.
There have now been nine Junes since 1909 where the departure from average has been greater than 1.0C.
Of those nine instances, five have been since the year 2000 and eight since 1970.
"Dozens" of climate stations placed in the top four for the warmest June ever recorded, Niwa said.
A persistent lack of southerlies had a profound impact on the monthly temperatures. Only one climate station in Middlemarch experienced a June mean temperature that was not either above average or well above average, Niwa said.
June weather highlights:
• The highest temperature was 22.2C, observed at Waione in Hawke's Bay on June 8.
• The lowest temperature was -7.4C, observed at Hanmer Forest in North Canterbury on June 1.
• The highest one-day rainfall was 137 millimetres, recorded at Te Puke in the western Bay of Plenty on June 11.
• The highest wind gust was 161 kmh, at Cape Turnagain on June 21.
• Of the six main centres, Dunedin was the driest and cloudiest, Auckland was the sunniest and warmest, Tauranga the wettest, and Christchurch the coolest.
• Of the available, regularly reporting sunshine observation sites, the sunniest four centres so far in 2014 (January to June) are: Whakatane (1392 hours), Tauranga (1261 hours), Auckland – Albany (1214 hours) and Takaka (1207 hours).