Wintry southerly blast could bring flooding, snow

A wintry southerly blast is about to pound New Zealand and could result in parts of Canterbury being flooded. 

According to a new forecast from Weatherwatch, a large low system is developing in the Tasman Sea and will soon cross over New Zealand. 

Coupled with a "very powerful high pressure belt" stretched over Australia and down south of New Zealand, it's expected the systems will "dredge up a wintry southerly blast" and also "pull down moisture-rich air from the sub-tropics".

Most of that moisture is going to be funnelled into Canterbury over the weekend and early next week with some parts of the southern region potentially lined up to see 200mm of rain in just two days.

"If this occurs flooding and slips will be highly likely, as parts of low lying Canterbury have been known to flood with just 30mm in a day," Weatherwatch says.

The colder air will also turn rain into snow with 80cm possible along the Southern Alps. Weatherwatch says there could be pockets of snow exceeding 1m over the weekend.

But northern parts of the country may escape mostly unscathed over the weekend. The north-east of the country can expect a drier than average next seven days while central New Zealand will likely enjoy "calm, settled weather".

"However, by early next week all of NZ gets the southerly – before another high rolls in. The fairly deep low coupled with the high pressure belt in Aussie will help push up wave heights in the Tasman Sea with peaks over 10 metres at sea making for increasingly rougher beach conditions along western and southern NZ this weekend."