Temperatures are warmer than usual on the first day of meteorological winter due to an interaction between strong northwesterly winds and the Southern Alps.
But don't get accustomed to it.
The conditions are being driven by a dry wind emanating from the west, with MetService issuing strong wind warnings for the Canterbury High Country, Fiordland and Stewart Island.
Strong wind watches were also in place for Central Otago, Queenstown Lakes, inland Southland and Canterbury, Marlborough, Wellington and Wairarapa.
Christchurch was currently the warmest centre in New Zealand at 20°C, with Kaikōura hitting 22°C earlier today.
MetService meteorologist Ngaire Wotherspoon told 1News "unusually strong" northwesterly winds, known as Foehn winds, were responsible for the bump in temperatures. Foehn was pronounced "fern".
As the air ascended over the mountains, it cools and — if there is enough moisture in the air — clouds can form.
Often, northwesterlies arriving on New Zealand's western coasts have enough moisture to produce not just cloud, but rain. That also explained why Westland was currently under a heavy rain watch, she said.
Wotherspoon said the loss of moisture meant "you get this really hot temperature dry wind coming down the other side".
Drier air warmed at a faster rate because there was less water to heat, she said.
"This is why we're seeing those really warm temperatures in eastern areas today."
She said there would be a "dramatic shift" in temperatures tonight when compared to Saturday's high.
"Alexandra has a forecast high of 20, but then overnight they are expected to get down to -1."
Five large fires wre currently burning across the South Island, fanned by the strong winds.
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