New Zealand's Climate

According to the Koeppen classification system New Zealand has a Cfb climate ("New Zealand"). This means it has a mild mid-latitude climate that is wet all year with mild winters and warm summers. Because the New Zealand islands are small, they experience relatively little temperature variation. The average variation between summer and winter is only about 10 degrees Celcius (Mullen).

This climograph of Auckland clearly demonstrates there is relatively little temperature variation between its coldest month (July) and its warmest month (February).
http://www.auckland.climatemps.com/

Due to its location between about 35 to 50 degrees south, one of the biggest factors affecting New Zealand's climate are the Westerly winds (Mullen). Because air moves from areas of high pressure to low pressure, the Westerlies originate in the warm high-pressure horse latitudes and move towards the cool low-pressure air near the poles. The Coriolis effect, which is caused by rotation of the Earth, steers the winds in New Zealand so that they tend to blow from the west and northwest ("Westerlies").

The arrows show the direction of the average wind from data collected between 1971 and 2000. The Westerlies are aptly named as the wind in New Zealand tends to come from the West.
 http://www.teara.govt.nz/en/diagram/7746/winds-over-the-southern-hemisphere

Cyclones are traveling low-pressure systems that sometimes develop in the Westerlies. These cyclones often bring rain and stormy weather to New Zealand (Mullen). However, the mountain ranges which run the length of the country create orographic precipitation and wind patterns. When the air rises over the mountains, it cools until it reaches the dew point, which results in precipitation. For this reason, many parts of the Southern Alps receive over 300 inches of rain a year, while some areas just east of the Alps receive an average of only 24 inches ("New Zealand Climate"). This is often referred to as a rain shadow.

Note the high rainfall on the west coast of the South Island. This is the windward side of the Southern Alps. Also notice that the areas east of the mountains receive much less rain.
http://www.teara.govt.nz/en/map/19595/new-zealand-annual-rainfall

Orthographic lifting sometimes creates foehn winds in the South Island. As the water vapor in the rising air condenses, latent heat is released so that the descending air is much warmer and dryer. In October of 2010, a weather station on the western side of the Southern Alps recorded a temperature of 57 degrees Fahrenheit. At the same time, the temperature at a weather station east of the mountains was 77 degrees Fahrenheit ("The Foehn Wind").

This animation demonstrates how a Foehn wind can create much warmer temperatures on the leeward side of a mountain range than on the windward side.
http://blog.metservice.com/2010/10/the-foehn-wind/

Works Cited

"Climate Data and Activities". NIWA Science. N.p., n.d. Web. 11 Nov. 2014.

"New Zealand". Weather Online. N.p., n.d. Web. 11 Nov. 2014.

"New Zealand Climate". MetService. N.p., n.d. 11 Nov 2014.

Mullan, Brett, Andrew Tait, and Craig Thompson. "Climate - New Zealand's Climate". Te Ara- The 
         Encyclopedia of New Zealand. N.p. 13 Jul. 2012. Web. 11 Nov. 2014.

Webster, Chris. "The Foehn Wind". MetService Blog. N.p. 18 Oct. 2010. Web. 11 Nov. 2014. 

"Westerlies". Wikipedia. N.p., n.d. Web 11 Nov. 2014.