Rachel Ashton plays with her pug Frankie on the summit of Auckland’s Mt Roskill as the sun sets on a crisp winter evening last Wednesday. June could set a new temperature record. Photo / Jason Oxenham
What’s expected to go down as New Zealand’s warmest June on record will be followed by more unseasonably mild weather over the next three months, Niwa’s just-issued outlookpredicts.
But, unlike last month’s generally tidy conditions, it’s likely to come with more week-to-week swings.
The agency predicted that, overall, temperatures were “very unlikely” to be colder than average between now and the end of September, although occasional cold snaps and frosts could still happen.
Above average temperatures were most likely for the east and west of the South Island, with about equal chances for above average or near average temperatures elsewhere.
But more heavy rainfall events were also possible over the coming months – especially in eastern areas – and some of them could be fuelled by “atmospheric rivers” connecting to the subtropics, which powered Canterbury and Gisborne’s recent deluges.
Generally, Niwa predicted rainfall levels were equally likely to be near or above normal in the east of the North Island and west of the South Island, and near near normal elsewhere.
As well, lower than normal air pressure – particularly to the west of the country – could help bring in more westerly and northwesterly winds than usual throughout the rest of winter and early spring.
Niwa meteorologist Ben Noll said New Zealand had likely just experienced its warmest start to winter – June’s record was still to be confirmed – and now Kiwis could expect to see more “variable” weather.
“Over June we saw a large area of high pressure that was sitting to the south and east of the country, and they helped to cradle those northerly lows as they tracked down,” he said.
“Whereas if we go through July, the week-to-week variability – the ups-and-downs – will be more prominent than in the past, where it’s just been consistently warm.
“We can expect more low pressure systems coming in from the west rather than the north, which will mean, temperature-wise, we won’t be quite as warm over the next two months.”
Soil moisture levels and river flows, meanwhile, were equally likely to be near normal or above normal in the east of the South Island, and most likely to be near normal in all other regions.
“I think farmers would be pretty pleased that we’re expecting at least near-normal rainfall for the next three months,” Noll said.
As for skifields, which welcomed this week’s polar blast after seeing a lack of snow, Noll said the chances of getting more decent dumps came down to timing.
“When these predicted cold snaps come through, will there be enough moisture there to have snow fall on skifields?” he said.
“But if we’re expecting things to be a bit more variable than last month, the opportunities for snow are definitely higher.
What we could be more sure of, he added, was that Kiwis would be using their heaters much more than they did last month.
Niwa’s outlook singled out a key factor for the balmy June: that coastal sea surface temperatures had been ranged between from 0.9C and 1.3C above normal over the month.
Other drivers had been a large swathe of warm ocean in the West Pacific – something which packed more energy into the recent storms – along with the cold to our south being locked up by an unusually strong polar vortex, and the background influence of climate change.
While the tropical Pacific was currently stuck in a climate state between La Nina and El Nino – called El Nino/La Nina Southern Oscillation (ENSO) neutral – the Western Pacific still packed some remnant warmth from a now-faded La Nina event.
The outlook comes as MetService is forecasting mostly fine weather throughout the country this weekend.
Saturday and Sunday were forecast to be mainly fine with morning frosts, and areas of cloud or fog in central parts of the North Island and valleys of the South Island.
On Sunday, any remaining showers about Gisborne and Northland were predicted to clear, while in the South Island, cloud was due to increase in the west, with light rain or drizzle in fiords and southern Westland.