The polar blast which roared across New Zealand was the most powerful storm in almost a decade.
The event was the right ingredients coming together, said MetService spokesman Daniel Corbett. "On Wednesday there was a surface low just to the northwest of the South Island and at the same time there was a southerly coming in with some cold air at the top of the atmosphere.
"The whole thing developed as a massive low that started to move across the west of the South Island, then [on Thursday] it moved across Cook Strait to create a new low just east of Kaikoura ... that was the real kick in pants that caused a clockwise circle of wind."
Associate Professor James Renwick at the School of Geography, Environment and Earth Sciences at Victoria University has researched how polar conditions affect our weather.
"To get an event like this, which is pretty extreme, we need the westerly wind that normally blows across New Zealand and the southern oceans to slow down and to buckle into a series of big meanders, north-south waves around the hemisphere."
