June tracking to be NZ's hottest amid warm and wet winter

New Zealand is on track to record its warmest June on record, with an unseasonably mild weekend forecast ahead of a surge of freezing air early next week. Photo / Brett Phibbs

New Zealand is on track to record its warmest June on record, with an unseasonably mild weekend forecast ahead of a surge of freezing air early next week.

Niwa meteorologist Ben Noll said the past few weeks had been substantially warmer than average across the country.

That had been prompted by warm sea temperatures in the western Pacific fuelling northerly low pressure systems bringing warm air to New Zealand.

Noll said the warmth was also due to a stronger-than-normal polar vortex.

"This is an expanse of cold, stormy air over Antarctica that has been particularly efficient at preventing outbreaks of cold air into the Southern Hemisphere mid-latitudes, especially in New Zealand."

Up until June 20 the nationwide average temperature was 10.97C, well above the long-term average of 8.59C.

"If the month ended today, it would become the country's warmest June on record, according to Niwa's seven-station series," Noll said.

The highest temperature was 22C at Leigh on June 19, and there were now more than 80 locations tracking toward a record or near-record warm month.

They included Kaitaia, Whangarei, Auckland, Gisborne, Whanganui, Palmerston North, Wellington, Nelson, Greymouth, Hokitika, Milford Sound and Wanaka.

Noll was predicting an unseasonably warm weekend coming up with mild nights in the 10C to 15C range and daytime temperatures possibly exceeding 20C in some places in the north and east of both islands.

Remnant warm water in the western Pacific, on the back of La Niña, has been a key driver of plumes of tropical moisture down toward New Zealand over the last several weeks 💧

There's likely more to come over the next several weeks as the pattern continues. pic.twitter.com/oPAwSRtDYJ

— NIWA Weather (@NiwaWeather) June 21, 2021

But, depending on location, the warmth wouldn't necessarily come with dry weather.

Heavy rain in Fiordland and the West Coast on Friday and Saturday could cause flooding and slips, resulting from a plume of tropical moisture extending down from southern Indonesia.

Strong northwesterly winds will buffet the Southern Alps and race through the Cook Strait and Wellington on Saturday and Sunday.

A surge of freezing air from the Southern Ocean could approach the country from next Monday or Tuesday, bringing a chance of snow to low levels and icy, strong southerly winds.

A return to milder conditions is possible during the first week of July.

Niwa research has shown that New Zealand winters have been consistently shorter than they once were.