The shortest day, the longest night - it's the winter solstice and yet the trees are flowering.
The National Institute of Water and Atmospheric Research (NIWA) predicted many places across the country were likely to record highs more typical of mid-April than late June.
It said Auckland and Hamilton were likely to challenge their record for 21 June of 17.8 degrees, with New Plymouth set to beat its 16.4 degree high.
Areas around the South Island, including Nelson and North Canterbury, were also likely to top their record highs for the day.
After the longest night last night, today is the shortest day - also known as the winter Solstice - when at 10.34am this morning, the sun's position in the sky will reach its farthest point north of the Equator.
NIWA meteorologist Ben Noll said the amount of daylight today varied across the country, but it would be about about 9 hours 37 minutes in Auckland, and 8 hours 35 minutes in Invercargill.
Writer Jolisa Greenwood tweeted a picture of her flowering daphne which monarch butterflies had not left all season.
Other users reported summer orchids and salmon catches as unseasonal highlights.
@meganjwhelan Regretting wearing a coat today as I walk to work— Natasha Frost (@natashamfrost) June 20, 2016
Mr Noll said a big storm over the Tasman sea was making its presence felt.
"And that's a warm flow, a sub-tropical flow, coming from a warmer place, and that draws the warm air southward and over New Zealand, and with the warm oceans temperatures surrounding the country, mix those things together and you're setting yourself up for a really warm day."
Even warmer temperatures were expected tomorrow.
This autumn was the second hottest on record, with a nationwide average temperature of 14.7 degrees celcius.