Weather: 'Significant spring storm' to hit New Zealand next week, major temperature plunge forecast

Watches and warnings are being issued for a "significant spring storm" preparing to hit New Zealand at the start of the week.

WeatherWatch says stormy weather will bring severe gales to both islands, pockets of heavy rain and heavy snow and a wintry temperature drop for the lower South Island in particular.

"A deepening low, and an active front preceded by strong and moist northwesterlies, approaches New Zealand from the west late this weekend," MetService reports.

"The front associated with the low moves northeastwards over the South Island on Monday and the North Island during Tuesday morning.

"Following the front, a very strong and cold southwest flow spreads over the country, which persists through until Wednesday or early Thursday, before a ridge of high pressure builds over New Zealand again."

MetService says this is forecast to deliver a period of heavy rain to western parts of the lower South Island, with a high confidence rainfall will reach warning criteria about Fiordland and Westland south of Otira and moderate confidence for the remainder of Westland, Buller, and the west of the Tasman region on Monday.

For Southland and eastern parts of Otago, there is moderate confidence of heavy southerly rain on Monday and Tuesday, then the confidence of heavy rain decreases to low on Wednesday.

WeatherWatch predicts temperatures will plunge significantly well-below normal from Tuesday with single-digit highs in some places in the south of New Zealand and then single-digit overnight lows across much of New Zealand.

Minimum temperatures may drop to near-freezing in some portions of the lower South Island.

"Additionally, snow will likely lower to around 600 metres about the lower South Island on Tuesday and Wednesday, and there is low confidence of heavy snow reaching warning criteria about southern parts of Central Otago and the Queenstown Lakes District," MetService says.

"However, heavy snow are possible at higher elevations in the surrounding regions, affecting some roads and high country farms but minimal confidence of reaching warning criteria."

There's also high confidence of severe northwest gales in exposed parts of Wellington and Wairarapa on Monday and Tuesday, and moderate confidence of severe northwest gales in exposed parts of the Canterbury High Country and Marlborough on Monday.

On Tuesday and Wednesday there is moderate confidence of severe westerly gales in exposed parts of the Tararua District and Hawkes Bay from Napier southwards.

Lastly, there is moderate confidence of severe south to southwest gales about coastal parts of Otago, Canterbury and the Kaikoura Coast on Tuesday and Wednesday, and low confidence about Wellington and Wairarapa on Wednesday.