Gusty winds have been building since this morning, and had spread north into Wellington, particularly the Rimutaka Range and Castlepoint in Wairarapa, where gusts of up to 65km/h have already been recorded, MetService meteorologist Marylin Avery said.
The winds were "just starting to pick up," she said, with the region expected to get windier into this evening.
"We've got quite a strong westerly wind spreading over the country, and behind it there's a cold southerly outbreak," she said.
"We're going to expect some snow to low levels overnight, and probably in Southland and Clutha tomorrow."
Ms Avery said westerly and northwesterly gales in Canterbury would spread over most of the country later today and into tomorrow.
In a weather warning issued this morning, MetService predicted gales gusting up to 130km/h would batter exposed parts of the Canterbury high country and foothills today, easing this evening.
A watch is in place for the possibility of severe northwest gales in some eastern areas.
A burst of heavy rain and possible thunderstorms were expected about the Tararua Range from tonight until mid-morning, when 60mm to 80mm was expected to accumulate over a nine hour period, MetService said.
"This amount of rain may cause streams and rivers to rise rapidly, and lead to slips," it warned.
Heavy rain was also expected in western parts of the country.
A northwest flow would bring rain, gales, thunderstorms and hail to much of the country, Ms Avery said.
"It's giving wintry weather for everybody."
In Auckland, the shock change from a warm and sunny autumn would come tomorrow, with the possibility of heavy rain, and squally thunderstorms with hail.
"You might not get as cold as it is down south, but there's still some nasty weather coming," Ms Avery said.
Behind the wind and rain, a cold front was looming, with a weather warning forecasting "significant" snowfall across Fiordland, Southland and Otago from this evening until Tuesday morning, above 300m, and particularly above 500m.
"So it's quite a cold outbreak coming up behind it," Ms Avery said.
"But it's not quite at the south coast [yet]. It's just poised to strike. They've got a bit of a southwest but not the real cold one yet."
The cold blast was expected to gradually ease off during the week, she said.
MAIN CENTRES FORECAST:
* Whangarei - Monday will see morning rain, heavy falls and then showers, a strong westerly and a high of 21C. Showers on Tuesday, with a strong southwest wind easing in the afternoon, a high of 17C.
* Auckland - Morning rain on Monday, with heavy falls turning to showers later, strong westerlies and a high of 19C. Temperatures look set to drop to 15C on Tuesday, as showers hit the region, some heavy, and a strong south-westerly easing in the afternoon.
* Hamilton - Monday will see morning rain then thundery showers, a strong westerly and a high of 17C. Showers, clearing and increasing to fine spells on Tuesday, with a southwest wind and a high of 14C.
* Tauranga - Rain around noon on Monday, then showers, strong westerlies and a high of 19C. Showers on Tuesday, clearing in the morning, fine spells increasing, a southwest wind and a high of 16C.
* Wellington - Early rain on Monday turns to showers, a strong northwest wind turning to a late southerly, and a high of 16C. Tuesday will see occasional showers, clearing by the afternoon, a strong cold southerly and a high of 12C.
* Christchurch - Showers on Monday, with hail developing, a cold southwest wind which strengthens during the day, and a high of 12C. More showers on Tuesday, and a strong cold southwesterly, with a high of 12C.
* Dunedin - Monday is likely to see showers with hail and a chance of thunder, a strong cold southwest and a high of 9C. Temperatures rise slightly on Tuesday, to a high of 11C, with showers easing in the evening, and a strong cold southwest wind.
(Source: MetService)
