Northland's warmest May on record has been shattered by the first frost of the winter, but weather forecasters say June should be milder than normal for the region.

Virtually the whole of the country experienced a record warm May, while in Northland, Whangarei, Kaitaia, Kaikohe and Kerikeri all had their highest ever mean maximum and minimum temperatures for the month.

The climate summary for May released yesterday by Niwa said, during the month, lower than normal air pressure, frequent northwesterlies and warmer than usual sea-surface temperatures contributed to the exceptional warmth felt across New Zealand.

In Northland, Kaitaia recorded a mean maximum air temperature for the month of 21.3C, which is 3C higher than normal and its highest since records there began in 1948.

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Kerikeri had a mean maximum of 21.2C, which is 2.6C above normal and the highest since records began there in 1981 while Kaikohe had a mean maximum of 19.9C, 3.1C above normal and the highest since records there began in 1973. Whangarei, meanwhile, had a mean maximum of 20.8C, 2.7C above normal and the highest since records started in 1967. All four centres also recorded their highest mean minimum temperatures ever for May, with Kaitaia at 13.7C (2.3C above normal); Kerikeri 12.1 (2.4C); Kaikohe 13.9C (3.3C) and Whangarei 13.4C (2.6C).

MetService meteorologist Lisa Murray said the maximums and minimums were significantly higher than the norm, and were reflected right across the country.

"A difference of 2.6C to 3.1C might not sound like much, but that's definitely noticeable, anything above 2C more than normal is really quite a significant difference and you would feel it," Ms Murray said.

"It's well above the norm. The most recent record highs were in 2011 and these have absolutely smashed them by a country mile."

However, yesterday saw the first ground frost in the region this year in places as temperatures dropped to 3C in Kaitaia and 5C in Paihia and Whangarei.

"Well, it is winter you know, and you've got the tail of the cold front that's been moving up the country," Ms Murray said. While the start of June has been a bit cooler across the country, next week would get back to above-normal temperatures for the time of year.

This long weekend will also see some fairly nice weather for the time of year, with plenty of sunshine, some cloud and the possibility of some scattered showers.