Weather: New Zealand's 2020 winter to be among warmest on record

There were three key ingredients that made New Zealand's winter this year "remarkable" and one for the record books, according to NIWA meteorologist Chris Brandolino. 

As Kiwis get ready for the start of spring next week, NIWA says this winter has been among the warmest on record.

"When we look at the nation's temperature… it's been, in existence - the records go back to 1909 - we are looking at the top 3 warmest winters on record. We will see where exactly we sit - one, two or three - by the end of the month," Brandolino told The AM Show.

"A very warm winter. Obviously, when we are talking top 3 out of 110 winters. That's just remarkable. That's what we are going to be. It's been a warm winter. There have been cold days, of course, but they have been outweighed by the warm ones."

Three key ingredients were behind the recent warm weather, Brandolino said.

"There is a climate change component and that is because our Earth is warming. Yes, we have always had warm periods and warm spells, that's unquestionable. But, fertiliser works too. Grass would grow on its own but if you throw on fertiliser it grows more, it grows better, it grows faster. That's what happened."

"We have had a lack of southerlies, our ocean temperatures around our coast are anywhere from a half a degree to to more than a degree celsius above average for the time of year. 

"So warmer than usual ocean temperatures, a lack of southerlies and then you throw in climate change. Add those three together and you end up with a top 3 warm winter."

While the next week may be slightly chilly, the meteorologist says spring is also likely to be more tropical than usual. 

"When we look at September, October, November, what we call spring as a whole, we feel with high confidence it will be a warmer than average spring. A warmer than average spring doesn't mean there won't be cold days. A great marriage will have a bad stretch."

He said that could mean an earlier start to the agriculture season and more Kiwis may also be heading to the beach in November.

However, the dry weather won't be welcomed by all.

"On the flip side of the coin, we have got to watch the dryness. We talked about Auckland. The soils are where they should be in terms of moisture. Keep in mind, soils are like a sponge. When that sponge gets saturated, it can then release the water out into the streams and rivers and tributaries."

"The sponge has been saturated for the North Island. But for the South Island, that sponge is pretty darn dry. Particularly, central and southern parts of eastern Canterbury, northern Otago. As we are looking into the growing season and irrigation season not too far from now, that could be problematic because we need rain.

"Unfortunately, over the next three months, the entire South Island, we are tipping to be either near normal or below normal."

On Wednesday, NIWA said snow coverage has been "poor" this year, with some sites recording half their typical snow depth for this time of year.

Eleven stations saw "very little snow fall between the last week of July until this week", with the Arthurs Pass and Mt Philistine stations having the least.

NIWA snow experts Dr Christian Zammit and Dr Jono Conway say there is often a hiatus in snowfall during mid-winter when large high-pressure systems cover the South Island, producing settled weather. 

"This often occurs around late July, but this year seems to have been longer and stronger than usual.”

The snow experts say warmer winters in the future are expected to cause more rain and less snow, especially at mid and low elevations.

"At higher elevations, changes in the total amount of precipitation may result in increases or decreases in snowfall depending on whether a region is getting wetter or drier. Again, because of the large year-to-year variability we are likely to see years with lots of snow and years with very little."