How to measure? Is it the smaller isolated but severe events, widespread events which are generally less severe but effect more people, or measured by the cost of the damage or lives?
Many severe events in the distant past will have been missed due the lack of population and communication or not caused as much damage given the extra vegetation of a century or so ago.

One of the biggest for me was Cyclone Alison in 1975, but that was overshadowed by the NW blast later in the year which caused more widespread damage.

1973 temperature records set in eastern South Island reaching 42deg C in Rangiora and somewhere in Marlborough – Blenhiem?

I think the storm in July of 2007 caught a few of us by surprise. Especially North of Auckland, where the power was out for 5 days.

This storm may not have been “big”, but it killed 21 people:

http://www.nzhistory.net.nz/21-people-drowned-after-cloudburst-at-kopuawhara

Thanks, that’s a good ‘starter for 10’ to begin with.

In my opinion, in order to be rated amongst the nations biggest 5 weather events, an event would either have to cause significant disruption over a wide area of the country – not just be restricted to one region – or if it was an event focused on one region then the impact must be so severe – perhaps deadly – that it was felt nation-wide.

To that end I would add – as most people would – the August 2011 snowstorm, as that was a truly national event. I would also take away the weather bombs of 2002 and 2008, as well as Drena and Fergus, as they did not do any major damage over a wide enough area.

I would also retain Cyclones Giselle and Bola, and the windstorm of ’75. I would also retain the 1992 snowstorm in Canterbury, but only because it had such a severe impact on farmers cause so many lambs died (1 million plus).

My Top 6 (only because I have a 3 way tie for 4th) would be as follows:

1) Cyclone Giselle.
2) Cyclone Bola.
3) 1975 windstorm.
4=) Nationwide snowstorms of 1939 & 2011, and the 1992 Canty snowstorm.

Having said that, Wikipedia has a list of NZ’s worst disasters by death toll at the following link:

http://en.wikipedia.org/wiki/List_of_New_Zealand_disasters_by_death_toll

I would think that any of these that are strictly weather related should be taken into consideration for this list.

http://www.teara.govt.nz/en/floods/1 has excellent stories,Maori mythology & images.

There was also the 1936 storm as well in the north island.