2017 I think. There was a massive storm and floods on North Island that made travel difficult. Just tried googling, sounds likes it happening again.You were very very unlucky. They are the best months. We used to live there. December was usually rubbish but Feb, March, April and even may was much warmer and sunnier than the UK.
What year were you there?
Don't get me wrong, it wasnt raining much and it was shorts and teeshirt weather, but it was grey and overcast a lot - much like a UK summer.
Still a fantastic place to go motorhoming. I wish we had the NZMCA instead of the crappy caravan club.