Summer in New Zealand is warm, without too much heat and humidity, with average temperatures around 25 °C. There is a lot of sunshine, and rains are very rare. New Zealand receives over 2,000 hours of sunshine a year. And daylight during the summer lasts up until 9 pm.
However, when you are exploring New Zealand, you have to take into consideration its position. The north of the country enjoys the subtropical climate. If you move to the south of the country, the temperatures generally get cooler, especially during the night. Sometimes in the summer polar air can blow towards the islands, then it gets a bit chilly. So if you plan to visit Queenstown or Fiordland National Park, pack some warm clothes. You'll need an umbrella too because summer is the rainy time on the South Island.