I went NZ last march/april and the weather was very mixed.
In the north island, especially at Rotorua and Auckland it was very hot (Im from the UK, so my version of very hot may be a lot different to yours !!). Whereas the South Island got a little cooler i did find it pretty warm, and a word of warning, apparently Wellington was having really good weather but it was very very windy so i ended up going buying a top. I took a fleece, waterproof and bought a ziptop but hardly (if ever) used the fleece and waterproof
On a seperate note, if you fancy skydiving when your there i wouldnt neccessarily wait until you reach a specific resort if the weather isnt great. I met up with my sister in the South Island and she almost missed out on a skydive as we waited until Queenstown and unfortunately it was cancelled due to the wind. Luckily it cleared up in Christchurch and we skydived on the 2nd to last day there.
Only my opinion but if its something youve got your heart set on then do it anywhere you get the chance