This time last week 15 towns and cities across New Zealand were on track for their warmest May on record - some were recording temperatures more like early summer by mid month.

By the end of the weekend just three were still in with a chance. On Monday, they too fell out of the running. 

The typically sub-tropical Whangarei dropped to 0.8 degrees Celsius on Wednesday morning, its coldest May temperature since 1976, according to Niwa.

Auckland, Hamilton, Whangarei, and Thames were all colder than Christchurch and Dunedin overnight. But the coldest temperature of the year so far was in Ranfurly and Middlemarch in Central Otago where it was -6C.

ROBYN EDIE/STUFF

Robyn Pickett, of Invercargill, walks her dog Midas in Queens Park, during the first decent frost of winter.

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It hasn't been that cold anywhere in the country since last September, Niwa said.

Wednesday night was expected to be cold again. 

Niwa meteorologist Ben Noll was expecting more near records - and Whangarei could break its coldest May temperature record of 0.6 C.

The cause of the changeable weather was the lack of a prevalent climate pattern.

"For months we'd had a La Nina weather pattern which brings more warm northerly winds our way. Then it was like the rug was pulled out from underneath this global climate driver and we got something completely different," Noll said. 

John Hawkins/Stuff

Frost sparkled in the early morning sunlight as commuters passed the Invercargill cenotaph on Dee St.

Now, we were in limbo without either La Nina or El Nino driving the climate, he said.

That meant a lot of variable weather was likely on the way.

"Basically, once April came ... La Nina faded away and it gave way to a much more variable pattern. The wind flow patterns around New Zealand responded to that change and we saw for the first time in a long time southwesterly winds.

"That has persisted off and on over the course of the last two months.

But it was not an indicator of the coming winter as a whole.  

"The interesting things is that going forward into June there is some indication that the pattern may go bounce back in the direction of La Nina," Noll said.

"We wouldn't go into an official La Nina again but that means the climate could behave in a La Nina-like manner. So a lot of people may be sitting there right now like 'wow, its cold now is this a sign that this winter is going to be brutal, awful, terrible?'

JOHN HAWKINS.STUFF

Southlanders awoke to a frost covered landscape on Tuesday morning.

"I guess my piece of advice to that is hold on a second here. The climate system has a memory. The sea surface temperatures they have a long term memory so often you se them going back to where they once were. 

"In the climate system things don't typically disappear without a trace so the fact that we've had this last two month period where things have been up and down, the ocean remembers that it was in La Nina for a long time preceding this two month period so I would expect us to bounce back into La Nina like conditions. 

"It's somewhat unlikely that it will end up being a record cold winter - in my opinion."

Conditions would turn slightly milder at times during the first half of June and we were not necessarily in for a winter with regular record-breaking cold, Noll said.

However, the periodic sharp cold snaps that we have experienced this week could continue. 

Earlier in May, Niwa principal scientist Chris Brandolino said a rapidly changing climate probably played a part in our uncharacteristic weather.

This summer was the country's hottest on record and while it's hard to tell what Winter holds, July is looking to be warmer than usual too.

"Our earth is warmer than it was 20 years ago. I'm sure there's a bit of a climate change component to it. 

"I don't want to say it's caused by climate change, but everything is influenced by climate change." 

 - Stuff