The first thing you need to know about New Zealand's climate is that its seasons are the opposite to those in the Northern Hemisphere. 
The best months for touring are October, November and February, March, April. May is recommended for photographers seeking clear blue-sky days and stunning autumn (fall)    colours reflected in mountain lakes, August and September are perfect for skiing. 

Overall, New Zealand has a very mild and temperate climate making it a suitable holiday destination all year round.

New Zealand comprises of two long narrow islands that run north-south and, as such, there is a huge difference in the climates of the top of the North Island, which is sub-tropical and the bottom of the South Island, which can be sub-antarctic at times! The temperature rarely rises above 30°C and will not stay long below 0°C except of course in the ski zones. 

The average rainfall varies considerably, from less than 400mm in Central Otago on the eastern side of the Southern Alps, to 12,000mm on the west coast of the South Island. The North Island and the east and north of the South Island is mostly dry in the summer months, and in the winter months it is mostly dry on the west and east coasts of the South Island. Confused? Just remember that this is a green land completely unlike Australia, with lush rain forests and many ferns, so bring your rain jacket as chances are you will experience rain somewhere on your trip!