Weather: High-risk months for 'sudden polar blasts' coming up, major snowstorms could hit New Zealand

Kiwis are being told to be prepared for winter storms up to October.
Kiwis are being told to be prepared for winter storms up to October. Photo credit: Getty Images / WeatherWatch

Forecasters are warning the danger months for "sudden polar blasts" are coming up - and New Zealand could be hit by "some of our biggest snowstorms".

"While the consistent run of freezing cold days may be thawing, August and September are high-risk months for sudden polar blasts. They may not linger as long as they do in June or July but they can be aggressive," says WeatherWatch's head forecaster Philip Duncan.

Duncan says Kiwis should "be prepared for winter storms right up to October".

He says traditionally August and September can bring "some of our biggest snowstorms" - so it's still far too early to say the winter weather is over.

"Worse, it may still be on the way and severe frosts may still return.

"But the consistent run of very cold weather at the end of June and start of July (an Antarctic blast, followed by a slightly weaker Southern Ocean blast) may now be replaced by more windier westerly weather - and that usually lifts overnight temperatures."

Duncan says those holding out for summer to return "may be pleased to know that it's possible we have passed the peak coldest point of winter now".

"By early to mid-August we'll be able to confidently say this."

In the shorter term, MetService is forecasting a narrow ridge of high pressure will move over the country this week.

However, the fine weather will be "short-lived", as another low-pressure system is set to bring showers to the southwest of the South Island by the end of Tuesday.

"This next system is expected to move across the country from late Wednesday and Thursday, bringing rain to many regions," says MetService meteorologist Amy Rossiter. 

"Areas exposed to the northerly flow, mainly the western and northern parts of both Islands are expected to be the focus of this rain, with potential for heavy falls about the higher ground.

"It's worth noting this system is expected to move across the country faster, and with lower rainfall accumulations than what we saw this past weekend," Rossiter says.