Climate Summary for August 2023

04 September 2023

New Zealand’s coldest August in seven years

Temperature	Temperatures were below average (0.51-1.20°C below average) across most of the North Island, and the top and west of the South Island. Some isolated areas also experienced well below average temperatures (<1.20°C below average) in the North Island and top of the South Island. The remainder of New Zealand experienced near average temperatures (±0.50°C of average).
Rainfall	Rainfall was below normal (50-79% of normal) or well below normal (<50% of normal) for the eastern, central and northern parts of the North Island, as well as much of the South Island. A small area of above normal rainfall (120-149% of normal) was observed in the southern Wairarapa and the lower South Island. Near normal rainfall (80-119% of normal) was experienced in Manawatū-Whanganui, parts of Wellington, parts of Otago, and much of Southland.
Soil Moisture	At the end of the month, soil moisture levels were below normal about East Cape, inland South Canterbury, and Marlborough Sounds. Soil moisture levels were above normal for parts of eastern Otago and the North Canterbury. Elsewhere, soil moisture levels were near normal.

Overview

August was the first month since May 2017 that Aotearoa New Zealand experienced colder-than-average temperatures, and it was the coldest August since 2016. The nationwide average temperature in August 2023 was 8.4°C. This was 0.55°C below the 1991-2020 August average according to NIWA’s seven station temperature series, which began in 1909, and just scraping in as “below average” (the threshold for below average is more than 0.5°C below the 1991-2020 average).

These below average temperatures owed to higher-than-normal pressures in the Tasman Sea and to the southeast of New Zealand. This allowed for more frequent southerly airflows, which brought cool and dry air from the south, a pattern indicative of a developing El Niño.

With several cold outbreaks and sea-level snow for southern parts, temperatures were below average (0.51-1.20°C below average) across most of the North Island, and the top and west of the South Island. Some pockets of the North Island also experienced well below average temperatures (<1.20°C below average). The remainder of New Zealand generally experienced near average temperatures (±0.50°C of average).

A lack of moist, northerly quarter air flows and higher-than-normal pressures contributed to generally dry conditions for most of New Zealand. Rainfall was below normal (50-79% of normal) or well below normal (<50% of normal) for the east, central and northern parts of the North Island, as well as much of the South Island. A small area of above normal rainfall (120-149% of normal) was observed in southern Wairarapa and the lower South Island. Near normal rainfall (80-119% of normal) was experienced in the Manawatū-Whanganui, parts of Wellington, parts of Otago, and much of Southland.

Further highlights

The highest temperature was 21.2°C, observed at Hastings on 14 August.
The lowest temperature was -8.3°C, observed at Cass on 11 August.
The highest 1-day rainfall was 82 mm, recorded at Arthur’s Pass on 19 August.
The highest wind gust was 172 km/h, observed at South West Cape on 1 August.
Of the six main centres in August 2023, Christchurch was the coldest, Auckland was the warmest, Dunedin was the driest, Wellington was the wettest, Tauranga was the sunniest, and Hamilton was the least sunny.
Of the available, regularly reporting sunshine observation sites, the sunniest four locations in 2023 so far are wider Nelson (1644 hours), Mackenzie Basin (1617 hours), Taranaki (1605 hours) and Tasman (1586 hours).