New Zealand is expected to endure extreme temperature fluctuations from warm to cold, as well as wind direction changes over the next couple of weeks. I mentioned winter in the title because in New Zealand, winter takes place in June, July, and August, while summer is in December, January, and February.
This is due to the position of New Zealand on the Earth. Seasons are determined by the proximity of regions to the sun. When the region that New Zealand is in is facing the sun, it is summer there, when the planet rotates and that side of it points away from the sun, winter can be expected. [Source]