Warmest winter yet fading out to a fine start to spring

New Zealand has experienced one of the warmest winters since records began in the mid-19th century, a climate expert says.

This year has brought on unseasonably warm temperatures during late July and throughout August, with an average 9.5C.

The normal average during this time is 8.3C.

Climate scientist Dr Jim Salinger said this winter had been one of the warmest since records began in the 1860s, with temperatures normally expected in spring and early summer coming a month early.

"The door to cold spells from the southern oceans - apart from a brief surge in June - has been well and truly closed this winter.

"September-like temperatures have been occurring throughout August, giving the country its warmest winter and August ever," Dr Salinger said.

Before this year, the warmest winter was in 1998, when an average 9.3C was recorded.

Other warm winters were recorded in 2001, with an average of 9.1C, 1984 (9C) and 1916 (8.8C).

Dr Salinger said records showed a "warming trend" over time.

"The clearest climate warming signal is seen in winter, where temperatures are now 1.1 degrees warmer than they were around 1870," he said.

"The warming trends have been very consistent, especially since the 1950s, when frosty days have decreased dramatically across the country."

In its latest seasonal climate outlook, the Niwa climate centre says the above average temperatures in August would also bring warmer than normal temperatures next month and in October.

Rainfall around the country is forecast to be normal and there would still be frosty conditions in some parts.

"Cold snaps, frost and snow conditions will of course still occur in many areas from time to time, as is typical of this time of year," the outlook reads.

WeatherWatch head analyst Philip Duncan said temperatures in Auckland and around the North Island were usually around 15C in August, but had been getting up to 18C, 19C and the early 20s.

"It's been an unusual winter ... and you can see it.

"Everything looks different for this time of the year.

"We've seen plants that were flowering in the middle of winter, that should have been flowering in the middle of September."

Meanwhile, the MetService says the country can look forward to a fine start to spring next week.

Forecaster Erick Brenstrum said a huge anticyclone was on the cards for the last day of August - signalling a fine day for the first day of September.

"We're expecting a fine start to spring in Auckland and probably in quite a lot of places.

"The first two or three days of spring looks like settled weather at this stage," Mr Brenstrum said.

The last week of August is forecast to bring a mix of fine weather and showers for both the North and South Islands.

Warmest winters

* 2013: Average temp of 9.5C.
* 2005: 9.1C.
* 1998: 9.3C.
* 1984: 9.0C.
* 1916: 8.8C.
* 1873: 8.0C.

Spring outlook

* First few days of Sept: Fine and settled weather in Auckland and most parts of the country.
* Temperatures in North Island and upper South Island predicted to be above average.
* Cold snaps, frosty and snow expected in lower South Island at times.