Summer (December to February) is usually warm. Dry in the east and wet on the west side. Winter (June to August) is wet in the north and coldish in the south. You can still get fine periods in the winter though but it is usually the wettest part of the year. Summer is the camping season. Winter is the sking season (of course). There are many good ski fields to choose from. I suggest tramping in the bush during the summer. Just be prepared if you go out into the bush (forest) especially the Mountains The weather all year can change within hours from good to horrible and if you are unprepared you can get into a lot of difficulty quickly. Make sure you make people aware of where you are going when you head out into the mountains as well for if you get into difficulty (e.g. injured ) it can make it very hard for rescuers to find you or get to you. If you are well prepared you will have a great time. I suggest checking the Department of Conservation website.

Thanks, David Lorier-May, for all the great info on New Zealand's weather & the alert about preparation for forest exploration. Hopefully, I will be able to travel there in the near future.