Wanganui sweltered last month under some of the warmest December temperatures experienced in recent years.
December was a significantly warmer month than average for most of the North Island, including Wanganui, according to figures released this week by Niwa.
Andrew Tait, a Niwa climate scientist, said Wanganui's top temperature of the month, 29.7C, on the 24th, was the hottest December temperature since records began in 1987.
"It was a very warm month over the whole North Island and parts of the South Island," Dr Tait said.
The coldest temperature in Wanganui last month was 8.4C, on the 4th.
Wanganui's mean temperature for the month was 17.8C, which was 1.2C above the average mean temperature for December and the fourth highest recorded.
Also fourth highest was the overnight minimum temperature of 19.4C recorded on the 22nd.
Dr Tait said an increase in mean temperatures of around 1C was significant. He said during December a lot more anti-cyclones than usual were lying east of the country.
"This drew northerlies and north-westerlies down onto the North Island particularly, which brought warmer weather.
"To top this off, ex-Cyclone Evan tracked down and just skipped over the top of Northland, bringing a very hot air mass. This was responsible for the very warm weather over the Christmas period," Dr Tait said.
The predominance of northerlies, and the warm air, meant that strong winds and thunderstorms were common.
Rainfall for the month was 90mm, compared to the December average of 86mm.