Over all New Zealand has a much warmer climate in the North Island year round, the Northland Region having the warmest temperature during the New Zealand winter and is some times refered to as the winter less North, the very top of the North Island is also very dry during the summer months and can flood during the winter months.
The North island has a prevailng south west wind direction which pushes the swell along the west coast from the south west direction and this wild mix of rough water is what makes the west coast so much different than the east coast, the waves and big ocean swells erode away the rocky coastline forming the high cliffs that are predominant on the coast and the same swells form the open sandy beaches in this part of the country.
The central plateau region around Lake Taupo and the great Mountains of Ruapahu, Tongaroiro and Ngauruhoe are the coldest regions of the North Island and are great skiing destinations in the winter, the Desert road on eastern side of the mountains is a cold and desolote place in the winter and one of the most dangerous to drive on, in contrast this area is stunning during the summer months with a warm climate for a few months of the year and draw tourists here for the lakes and the trout fishing.
The regions south of the great mountains and down to Wellington are some times prone to flooding as there are a lot of rivers in this region and alot of flat land as well, the bottom regions of the North Island around the Wellington area are prone to windy conditions as they catch the wind from across the Cook Straight and also from the west coast as well.
The coldest months in New Zealand are around april to september and the warmest from october to march, the South Island is mostly covered in snow for the winter months particually the high plateaus and the mountains and these areas can be very deslote and dangerous places in the middle of winter, the predoment wind direction is from the south west and the coast line is much the same as the North Island with a rugged coast and high mountains running up to the edge of the coastline.
The South Island East Coast is open and flat in most places and can have servere drought conditions in the summer time, although this can vary from year to year, there are numerous rivers that flow down from the mountain ranges of the central South Island but there is not alot of rain fall in places and alot of the farming community rely on the water from these rivers for irrigation, the wettest place goes to the Milford sound area and generally the south eastern corner of the south Island here they can get several metres of rain fall a year.