A slow slide into winter for most Kiwis during the next few weeks

Tuesday, 7 May 2019

New Zealand may be stepping closer to winter each day, but it could still be a couple of weeks before the change goes from imperceptible to obvious.

Forecasters say the broad weather patterns across the country and surrounding oceans are this week starting to shift into winter mode, with sea-surface temperatures having cooled to more average levels for the time of year around the North Island but a little warmer than normal further south.

After this week's unseasonably mild northerly weather, the latest advice is next week will become cooler with west or southwesterly winds across much of the country.

Forecasters say there are the earliest signs of snow in the far south by the end of May. A car drives across Three Mile Hill in Halfway Bush, Dunedin (file photo).

The following week may be much the same. But by the time we get to the last week of the month, starting May 27, there are the earliest indications of much colder, stormier weather, with a signal for snow in the south of the country, according to both MetService and Blue Skies Weather.

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Georgina Griffiths of MetService says there is a change going on to a winter weather pattern, with a signal for possible snow in the south in the last week of May.

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Of course that could all yet change. And when you look at it, that might mean proper winter would arrive at the start of the traditional calendar winter anyway.

Blue Skies Weather forecaster Tony Trewinnard, who thinks this winter could be cloudier than normal.

In the shorter term, MetService meteorologist Stephen Glassey said temperatures across the country would stay warmer than average this week, but a front would bring rain to western parts of both islands on Thursday and Friday.

A more active cold front on Sunday with a developing low-pressure system looked likely to bring another dose of briefly heavy rain to western places ahead of a colder southwesterly change.

Snow makes for a slippery drive up and down Stuart St in Dunedin.

'Behind that front we'll start getting some cooler temperatures. However, at this stage it's not looking like a real cold snap, just more of a return to what's normal for this time of the year,' he said.

Looking further ahead, MetService meteorologist Georgina Griffiths told Stuff the signs of change were there now in some of the models.

'It's quite clear that it's a regime shift under way.

'We've got the ridge [of high pressure] going back on to the North Island and westerlies across the South Island next week, and there will be some features in that. So there's a real dipole between dry in the north and fronts further south.

At the end of May, the models were showing quite a strong snow signal in the far south, Griffiths said.

'This ridge holding on to the North Island, this will be a problem, It has been very dry up here for many north of about Taupō.

'May is usually wetter and when there's a water recharge. But it doesn't look like we are going to get the real decent rains in that short-term,' she said.

Blue Skies Weather forecaster Tony Trewinnard said medium-range forecasting models had been suggesting an increasingly southwesterly-dominant weather pattern as May progressed.

Next week and the week after would be mostly westerly, with periods of wetter and colder weather in western and southern parts of the South Island but generally fine conditions in the east and for much of the North Island, with some cold nights.

'But before the end of May, we should start to see low-pressure systems becoming dominant for a time, and into the first week of June.

'It could well be a wet Queen's Birthday weekend, with some snowfalls further south.'

Trewinnard said it might be a cloudier than normal winter in many places.