The cold nights are set to continue over the next week, but the good news is the days will be warm and largely free of rain.
A "huge" high anchored in the Tasman Sea and stretching all the way to Fiji and halfway to Antarctica is to thank, according to WeatherWatch.
This "will bring a drier than average week ahead for New Zealand with warmer than average daytime highs but cooler than average nights, at least to begin with".
"Warmer sub-tropical winds are likely by Friday and this weekend, pushing temperatures up even further," WeatherWatch said on Monday.
MetService says because the high is so huge, the changes in atmospheric pressure are spread out over large distances - and this means any wind, even the cool southerlies, will be "gentle".
"The fact the air is piling down over the country from way up above us means that it's hard for any convection to occur," it said on Facebook. "It's hard to get the air to rise, cool, condense and form clouds and showers when the air above it is constantly pushing back down against it.
"So, while all this is going on in the background many of us will experience a generally fine and pleasant day. There will of course be the odd outlier with a few isolated showers and cloudy patches about the coasts but overall a fine start to the week."
By Friday sub-tropical winds will bring more warmth, pushing temperatures up but also increasing the chance of rain, which is likely to hit Fiordland, Southland and Westland.
WeatherWatch forecasts temperatures 8degC above average in the Mackenzie and southern Tasman regions during the days. Most of the South Island will be not far off, with the exception of the east coast.
In the north, Rotorua and Taupo will be the places to be if you want to taste of summer in October.
But at night, most of the country will be 2degC or more colder than usual at this time of year, Westland the only significant exception.