Under the Köppen climate classification, Auckland has an oceanic climate (Köppen climate classification Cfb), while according to the National Institute of Water and Atmospheric Research (NIWA), its climate is classified as subtropical with warm humid summers and mild damp winters. It is the warmest main centre of New Zealand and is also one of the sunniest, with an average of 2,003.1 sunshine hours per annum. The average daily maximum temperature is 23.7 °C (74.7 °F) in February and 14.7 °C (58.5 °F) in July. The absolute maximum recorded temperature is 34.4 °C (93.9 °F) on 12 February 2009, while the absolute minimum is −3.9 °C (25.0 °F), although there is also an unofficial low of −5.7 °C (21.7 °F) recorded at Riverhead Forest in June 1936. Snowfall is extremely rare: the most significant fall since the start of the 20th century was on 27 July 1939, when snow stuck to the clothes of people outdoors just before dawn and five centimetres (2 in) of snow reportedly lay on Mount Eden. Snowflakes were also seen on 28 July 1930 and 15 August 2011. The early morning calm on the isthmus during settled weather, before the sea breeze rises, was described as early as 1853: “In all seasons, the beauty of the day is in the early morning. At that time, generally, a solemn stillness holds, and a perfect calm prevails…”.
Auckland occasionally suffers from air pollution due to fine particle emissions. There are also occasional breaches of guideline levels of carbon monoxide. While maritime winds normally disperse the pollution relatively quickly it can sometimes become visible as smog, especially on calm winter days.