"The warmest places are expected to be Hawke's Bay and Northland, where we are forecasting a relatively balmy 20C for this time of year.
"On the flipside, the starry nights do mean that all that daytime heat is going to escape back into space, causing temperatures to drop significantly once the sun goes down."
The coldest night time temperatures were predicted for the South Island with Christchurch likely to dip to just a couple of degrees, while further inland Twizel and Pukaki may reach zero, Ms Blades said.
Spots in the North Island will also feel those cold nights, with Hamilton set to drop to 5C on both nights of the weekend.
But the temperatures would pick up again next week, as a warmer flow headed our way from across the Tasman Sea, she said. This moist air will bring some rain to western parts of the country towards the middle of next week.
Meanwhile, WeatherWatch.co.nz said winds today had lashed Auckland with average wind speeds sitting about the 50kmh thus far - with some passing squally showers in parts.
Winds had been pretty strong around eastern parts of the island, with Hamilton and Tauranga seeing some strong west and southwest gusts of about 40kmh too.