New Zealand's Climate
New Zealand is in the same hemisphere as South Africa and Australia, having a temperate climate with moderate, year-round rainfall and in the North Island especially, an absence of extreme temperatures.
The country enjoys a pleasant and generally stable climate. Average summer temperatures will be between 20 and 30 degrees Celsius and winter temperatures between 10 - 18 degrees.
New Zealand is long and narrow, stretching a distance of 1600 kilometres in a North to South direction and being no more than 450 kilometres wide, at its widest point. The North and South Islands have a combined area of approximately 268,000 square kilometres.
The sea moderates the climate bringing mild temperatures and a reliable climate throughout the year. The country is close to the International dateline and it is claimed that Gisborne, on the East Coast of the North Island is the first city in the world to see the light of each new day.
October through to April are the warmest months and May to September are the coolest. A typical summers day in the North will range in temperature between 24 and 30 degrees centigrade (72 and 86 Fahrenheit), while a mid-winters day will rarely fall below 14 or 15 degrees centigrade (around 52 Fahrenheit).
Auckland has never known snow. Or so I thought when I wrote this section some years ago. Apparently in 1939 it did snow in Auckland and a number of our extinct volcanoes had a dusting but it was well melted by morning tea time.
In the south it can be quite different or even in the north at higher elevations. Christchurch will occasionally have snow but is generally a very dry and sunny climate. Dunedin too is very dry with low year round rainfall but it is more likely than Christchurch to experience snow in winter.
Snow is generally not seen at sea level, though there is an abundance of snow during winter in the South Island high country and in the mountain ranges in the North Island. Both the North and South Islands have ample winter ski fields, with the South Island renowned for the majesty of its mountains and beauty of its woodlands, lakes and rivers.
Nelson, at the top of the South Island is the sunniest city in the country, however most of the country enjoys over 2000 hours of sunshine per year. The country is largely pollution free but on still winter days in Auckland and Christchurch air quality can certainly be at levels we should not be proud of.
Table 1: Average Rainfall and Average Sunshine Hours
Table 2: New Zealand's Climate Summary (1971 - 2000)
Data are mean annual values for the 1971 - 2000 period, for locations having at least 5 complete years of data. Extreme temperatures are for the full historical record. Monthly temperature and rainfall data for each location are recorded in separate tables.
NIWA Analysis of 2012
The year 2012 was rather dry and sunny in western areas of both Islands, but annual rainfall in eastern areas of both Islands was generally near normal or above normal. Many regions experienced a somewhat cool year.
Annual mean sea level pressures were slightly lower than usual across New Zealand in 2012, but the circulation anomaly for the year was rather weak. More easterly circulation than normal affected the country for the first five months of the year, as well as in August. A change took place in the second half of the year, with more frequent southwesterly airflows than usual in June, September, October, and November. July and December were influenced by frequent anticyclones, and more northerly quarter winds, overall.
The large-scale climate setting was primarily driven by a moderate La Niña event at the start of the year, but this eased back to neutral in autumn. Although ocean temperatures in the equatorial Pacific Ocean reached the El Niño threshold by spring, the atmosphere did not develop an El Niño pattern and neutral conditions continued through the remainder of 2012.
Mean annual temperatures were below average in the northeast of the South Island, as well as for Wellington, Wairarapa, parts of the Manawatu, and between the Tararua District and the Waikato. Mean annual temperatures were generally near or slightly below average elsewhere. The nation-wide average temperature for 2012 was 12.5°C (0.1°C below the 1971–2000 annual average), using NIWA's seven-station temperature series which begins in 1909 .
Annual rainfall totals for 2012 were below normal (less than 80 percent of annual normal) in western areas of the North Island between Wanganui and the Kapiti Coast, and for Fiordland. It was the driest year on record for Wanganui and Secretary Island. It was also a relatively dry year (with rainfall between 80 and 100 percent of annual normal) for the south, west, and north of the South Island, and across much of the remainder of the North Island (except for Gisborne). Above normal rainfall (more than 120 percent of annual normal) was observed in Gisborne, as well as for parts of Central Otago, and between Oamaru and Timaru.
The year 2012 was a sunny one for western areas of the North Island from Te Kuiti southwards to the Kapiti Coast, as well as for the West Coast of the South Island. It was the sunniest year on record for Te Kuiti, New Plymouth, Paraparaumu, and Greymouth. This sunshine pattern reflects the enhanced easterly winds that occurred for the first five months of the year, as well as in August. In contrast, below normal annual sunshine totals (below 95 percent of annual normal) were observed for the Wairarapa, Wellington, Blenheim, Central Otago, and Northland. Elsewhere, sunshine totals were generally close to the annual normal.
The year 2012 will be remembered for extremely heavy snowfall on 6 June. Snowfall was heavy and to very low levels over Canterbury, Arthur's Pass, Otago, West Coast, and Marlborough. Afternoon temperatures in Canterbury, Blenheim, around Arthurs Pass, and on the West Coast on the 6th set new low records for the month, and in some cases, broke all-time (any month) records, too. Maximum temperatures on 6 June in Canterbury struggled to reach even 1 degree, with heavy snow falling throughout the daylight hours.
And it was a year in which 14 tornadoes or waterspouts were observed, including a tornado which touched down near Hobsonville, Auckland, on 6 December, tragically killing three people.
Severe frosts were widespread and frequent in the second half of June; and unusually late frosts on 7 and 8 November were problematic for some.
Heat waves and extreme high temperatures were generally lacking in 2012. In January and February, La Niña's cloudy and wet conditions meant that the typical summertime swelter was absent. In contrast, winter warmth was periodically observed – with northerly winds producing unusual warmth during the second half of July, 25-27 August, the last two days of September, and the last week of October. Ex-Tropical Cyclone Evan slowly approached the northern North Island between 22 and 27 December, dragging very warm and humid subtropical air onto the country. Humidity levels were very high during this period over the North Island. The northeast air stream also produced extremely high Christmas Day and Boxing Day temperatures in western areas which were in the 'lee', namely Taranaki to Wellington, as well as Nelson. Elsewhere, numerous extreme maximum temperature records occurred during the week around Christmas due to warm windy northwesterly conditions.
In 2012, there were eight particularly notable rainfall events. On 22-23 February, heavy rain caused flooding and slips in Otago, Nelson, and the central North Island. A weather 'bomb' during 3-4 March caused heavy rain and extremely strong winds for the western and southern North Island, and Nelson. On 19 March, Northland was affected by widespread floodwaters due to a deep low stalling east of the Bay of Islands. This low moved south over the North Island on 20 March, all but isolating Gisborne by causing slips and tree-falls that blocked numerous roads. On 5 June, the northwest South Island was affected by record-breaking rain, associated with a rapidly deepening low over the Tasman Sea. On 16 July, flooding was widespread in many regions over the southern half of the North Island and the northern South Island. Westport was isolated, and numerous State Highways were closed due to slips and floodwaters. The Western Bay of Plenty and Coromandel were flooded in back-to-back events on 23 and 30 July. And several heavy rain events in the period to 1-15 August flooded parts of Marlborough, Canterbury, and north Otago.
For more (and with thanks to NIWA): http://www.niwa.co.nz/climate/summaries/annual/annual-climate-summary-2012