An active front barrelling up the South Island "like a freight train'' is leaving cool Antarctic air in its wake and threatening the eastern side of the country with 100km/h winds.
The strong winds brought by the front has resulted in a severe weather warning for Hawkes Bay, Wairarapa and Canterbury.
The front was dredging up cold Antarctic air from well south of New Zealand, WeatherWatch head weather analyst Philip Duncan said.
Daytime highs for the middle of January were well below average and would struggle to reach double digits in some areas tomorrow, he said.
For parts of coastal Southland and Otago, the highs would reach a mere 11C to 13C degrees tomorrow.
Despite its large size, the system didn't look like it would linger, Mr Duncan said.
Christchurch's high would shoot up back up to 27C on Sunday as the nor'westers returned, and Dunedin would bounce back up to 18C.
Regions far from the south, including Bay of Plenty and Gisborne, were seeing much hotter and drier weather, Mr Duncan said.
MetService spokesman Dan Corbett said the front was bringing the risk of thunderstorms to eastern parts of the South Island, along with some strong gusty winds, which would "barrel up the east coast of the South Island like a freight train''.
"It will move through Christchurch this evening and Wellington around midnight. Winds gusts in the southerly could get up to around 100km/h later today, early tonight.''
A severe weather warning was in place for Hawkes Bay, Wairarapa and Canterbury - where west to northwest gales were expected to gust around 120km/h this afternoon, before easing later in the evening, Mr Corbett said.
The winds had the potential to damage trees and powerlines, and make driving difficult, especially for high-sided vehicles and motorcycles.
The front would also bring cooler temperatures to across the south and east of the country and there could even be a dusting of snow across the Southern Alps in the far south down to around 1000m by early tomorrow, Mr Corbett said.
However, the cooler air would have little impact in the far north of the North Island.
Auckland, Hamilton and Tauranga could expect a few showers later tonight and early tomorrow followed by a gusty southwesterly, which would be particularly strong across eastern parts Coromandel and the Bay of Plenty, Mr Corbett said.
Meanwhile, looking forward to the weekend, an anticyclone building across the country would bring mostly fine and dry weather, he said.