April temps 'near average' after scorching first three months

April's cooler change was noticed more in the south. Queenstown's Remarkables skifield received a dump of 30cm of fresh snow late last month. Photo / The Remarkables

A cool change made April the first month in nearly a year that didn't finish up with above-average temperatures, as the big drivers of New Zealand's record-hot summer effectively ran out of gas.

Niwa meteorologist Ben Noll said just-released statistics for last month showed it was the first time since July 2017 that overall temperatures had been closer to average across most of the country.

April's nationwide average came in at 13.3C - just 0.1C above the 1981-2010 average, and officially putting it at "near average".

It wasn't the same everywhere: while near average temperatures were seen in the southeast of the North Island as well as parts of the central North Island, the rest of the north still got above average conditions.

In contrast, large parts of central Canterbury, Fiordland, and the West Coast felt the chill of below-average temperatures - or those that ranged between 0.5C to 1.2C below the baseline.

So what happened?

Noll pointed to the major factors that made summer the hottest on the books, and also gave 2018 the warmest first three months of any recorded.

A La Nina system that set in last year had been driving more winds from a northeasterly direction, and this influence went hand-in-hand with the positive phase of an effect called the Southern Annular Mode, which had been blocking colder winds from the south reaching New Zealand.

The La Nina had faded, as had a persistent and remarkably strong marine heatwave in the Tasman Sea that warmed up sea surface temperatures, with wide-ranging consequences for the country.

Mt Ruapehu's Turoa skifield received plenty of snow in the April 10-11 storm. Photo / Mt Ruapehu

In their place over April came more southwesterly winds than normal for much of the country, and several low pressure systems and cold fronts passed over the country.

The storms seen on April 10-11 and 28-29 were especially damaging, with the former bringing destructive winds and several tornadoes to some locations - notably Taranaki and Auckland - and the latter bringing heavy rain to parts of the country.

"The first couple of days of April were very warm, and while I know it might seem like a distant memory now, the month did have a very hot start," Noll said.

"But then there were several cool changes, and the South Island certainly felt it most - we had snow capping the mountains."

Auckland - and homes like this one in Massey - bore much of the brunt of a fierce storm that hit on April 10-11. Photo / File

The month's coldest temperature reading was recorded at Ranfurly, where the mercury dropped to -4.9C on April 14.

The warmest, meanwhile, was the 28.5C observed at Napier on April 4.

The record books also showed the highest amount of rainfall in a day (133mm at Te Puke on April 15); the highest wind gust (161km/h at Akitio on April 20).

Of the six main centres, Dunedin and Auckland were the wettest, Hamilton was the driest, Auckland was the warmest, Christchurch and Dunedin were the coolest, Tauranga was the sunniest, and Dunedin was least sunny.

Source / Niwa

Noll said the last time New Zealand saw a month where temperatures were below average was January last year, when Wellington suffered its miserable "bummer summer".

There was no indication of that happening again any time soon.

Temperatures over the next three months were forecast to be above average in the north of the North Island.

That included Northland, Auckland, Waikato and the Bay of Plenty; elsewhere, temperatures would likely be above average or average.

But Niwa reported frosts and cold snaps would still become more common, with some cold snaps "possibly quite sharp".

"Roughly a week to two weeks from now we can expect a couple more stronger southerly changes coming up the country, and that will lead to some colder conditions in mid-May."