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New Zealand Climate

(borrowed from NIWA)

New Zealand's climate is complex and varies from warm subtropical in the far north to cool temperate climates in the far south, with severe alpine conditions in the mountainous areas.

Mountain chains extending the length of New Zealand provide a barrier for the prevailing westerly winds, dividing the country into dramatically different climate regions. The West Coast of the South Island is the wettest area of New Zealand, whereas the area to the east of the mountains, just over 100 km away, is the driest.

Most areas of New Zealand have between 600 and 1600 mm of rainfall, spread throughout the year with a dry period during the summer. Over the northern and central areas of New Zealand more rainfall falls in winter than in summer, whereas for much of the southern part of New Zealand, winter is the season of least rainfall.

New Zealand Climate zones

New Zealand Climate Maps, click on image to enlarge


Mean annual temperatures range from 10°C in the south to 16°C in the north of New Zealand. The coldest month is usually July and the warmest month is usually January or February. In New Zealand generally there are relatively small variations between summer and winter temperatures, although inland and to the east of the ranges the variation is greater (up to 14°C). Temperatures also drop about 0.7°C for every 100 m of altitude.

Sunshine hours are relatively high in areas that are sheltered from the west and most of New Zealand would have at least 2000 hours annually. The midday summer solar radiation index (UVI) is often very high in most places and can be extreme in northern New Zealand and in mountainous areas. Autumn and spring UVI values can be high in most areas.

Most snow in New Zealand falls in the mountain areas. Snow rarely falls in the coastal areas of the North Island and west of the South Island, although the east and south of the South Island may experience some snow in winter. Frosts can occur anywhere in New Zealand and usually form on cold nights with clear skies and little wind.

See also Auckland Climate and We are upside down and Walker Circulation, El Nino and La Nina and Storm Surges

Niwa review of 2010

The country had relatively settled and warm weather last year with Whakatane being the sunniest followed by Nelson and Blenheim, the National Institute for Water and Atmospheric Research (Niwa) said today. Mt Ruapehu, Lake Tekapo and Mt Cook were the coldest. Cheviot had the highest temperature at 35.6degC while Lake Tekapo recorded the lowest at -12.6degC.

Increased anticyclones ('highs') brought relatively settled conditions throughout the country, Niwa said. “The broad climate setting switched from moderate El Nino early in the year to a La Nina by July. “The La Nina had become moderate-to-strong by September.”

Notable climate features included two droughts, several heat waves, and three significant rainfall events, it said. The wettest areas were Cropp River, Doon, and North Egmont with the driest at Clyde, Ranfurly and Alexandra.

The most rain in a single day at 314mm was recorded at Milford Sound on April 25. In the main centres, Tauranga was the sunniest, Wellington the wettest, Christchurch the driest and Auckland the warmest, Niwa said.

Niwa review of NZ weather 2012

Overview

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.

NIWA

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