Summer 2016-17: cool for most but dry in the north and east

New Zealand Climate Summary: Summer 2016-17 Issued: 3 March 2017

A cool summer for most but dry in the north and east

Overview

For the season as a whole, mean sea level pressures were below normal over New Zealand, with considerably lower than normal pressures present to the southwest of the country. This pressure pattern delivered more westerly and southwesterly winds than normal during the season. These winds resulted in cool and unsettled summer weather for many parts of the country, especially in southern and western regions which are exposed to southwesterly winds. In contrast, areas sheltered from the southwesterly airflow experienced warm and dry conditions for much of the summer. This was particularly evident in Hawke’s Bay and Gisborne, where daily maximum temperatures frequently exceeded 30°C and extended dry spells were observed. Sea surface temperatures surrounding New Zealand were typically lower than normal for the time of year, although these temperatures returned to near-normal towards the end of the season. Anticyclones (high pressure systems) prevailed over New Zealand throughout the latter half of February, resulting in a warm, dry and sunny end to summer for the majority of the country.

Summer temperatures were below average (-0.51°C to -1.20°C of the summer average) for western parts of Southland, the Southern Lakes, West Coast, Tasman, Wellington and Waikato. Well below average temperatures (< -1.20°C of the summer average) were observed at Te Kuiti, Takaka, Appleby and Mt Cook Village. In contrast, isolated parts of Hawke’s Bay and Gisborne observed above average temperatures (+0.51°C to +1.20°C), as did Rangiora (Canterbury) and Lauder (Central Otago). Temperatures were typically near average (-0.50°C to +0.50°C) for the remainder of the country. The nation-wide average temperature for summer 2016-17 was 16.3°C (0.4°C below the 1981-2010 summer average, using NIWA’s seven-station temperature series which begins in 1909). This is the coldest summer in five years (since 2011-12), and the fifth-coolest summer in the last 20 years (the colder ones in order being 1999-2000 (coldest), 2011-12, 2002-03, and 2004-05).

Rainfall was below normal (50-79% of the summer normal) in Auckland, Waikato, Gisborne, Nelson, Blenheim, and parts of Canterbury. It was a particularly dry summer for Northland and the East Cape where rainfall was well below normal (< 50% of the summer normal). In contrast, rainfall was above normal (120-149%) for the West Coast and Fiordland. Near normal rainfall (80-119%) was observed for remaining areas of New Zealand. Hawke’s Bay received very little rainfall during December and January, with Napier observing its third-driest January in records that began in 1870. However, considerable rainfall during February resulted in near normal rainfall totals in the region for the summer overall.

The abnormally dry start to summer for northern and eastern parts of the country contributed to soil moisture levels that were well below normal for the time of year in those areas. In early February, Northland’s drought was officially classified as a medium-scale adverse event by the Minister for Primary Industries. Many central and eastern parts of the North Island observed soil moisture levels that were well below normal during December, January and early February. However, farmers in these areas welcomed a considerable increase in soil moisture levels by the end of February, due to periods of heavy rainfall that occurred during mid-February. An extended period of settled and dry weather at the end of February resulted in soils becoming drier than normal over much of the South Island by the end of summer. In addition, as of 1 March 2017 soil moisture levels were below normal in Taranaki, and considerably below normal about the East Cape.

Summer sunshine was above normal (110-125%) for parts of Northland, Gisborne, Hawke’s Bay and Canterbury. In contrast, southeastern parts of the North Island observed below normal sunshine (75-89%). Remaining areas of the country typically observed near normal sunshine (90-109%). Summer was particularly dour in the southwest of the North Island; Wellington narrowly avoided a near-record low sunshine total for the season due to a 10-day period of mostly sunny weather at the end of February.

Further Highlights:

• The highest temperature was 35.5°C, observed at Wairoa on 6 February.

• The lowest temperature was -1.7°C, observed at Mt Cook Airport on 5 January.

• The highest 1-day rainfall was 309 mm, recorded at Milford Sound on 31 January.

• The highest wind gust was 178 km/hr, observed at Akitio on 13 February.

• Of the six main centres in summer 2016-17, Tauranga was the warmest and sunniest, Dunedin was the coolest, Christchurch was the driest, and Wellington was the wettest and cloudiest.

Full summary: Climate_Summary_Summer_2017_Final.docx

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