Weather: 2023 winter fifth-warmest on record, after chilly August offsets hot June and July temperatures

By RNZ

Aotearoa has just had the fifth-warmest winter on record, the relatively hot June and July offset somewhat by a below-average August - the first month since May 2017 with cooler temperatures than the 1991-2020 average.

“The nationwide average temperature in August 2023 was 8.4C,” the National Institute of Water and Atmospheric Research (Niwa) said in its latest Monthly Climate Summary, released on Monday.

“This was 0.55C 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 0.5C below the 1991-2020 average].”

The causes were two high-pressure zones - one in the Tasman Sea, the other to the southeast of the country - creating a corridor for “cool and dry air from the south, a pattern indicative of a developing El Nino”.

El Nino is a weather pattern that typically creates higher global temperatures.

Scientists predict 2024 will be the hottest on record.

But for now, the cool airflow caused below-average temperatures across most of the North Island and the top and west of the South, Niwa said.

Rainfall for August was below average too, without much in the way of moist northerly air. Over winter, rainfall was also below normal in most places, Niwa said in its Seasonal Climate Summary, also released on Monday.

But the east of the country was the exception, particularly Canterbury in late July.

“During this event, Christchurch, Akaroa, Leeston and Woodend each observed their wettest winter day on record,” Niwa said. The highest single-day recording was 199mm in Akaroa on July 22.

Auckland, which had its wettest month ever earlier this year, saw 282mm fall over winter - only a little more than what fell on January 27.

While it might have felt like the drizzle in Auckland has barely eased since the Anniversary Weekend downpour, the city actually had a below-normal amount of rain over winter.

Other centres experiencing record single-day rainfalls were Rings Beach (Coromandel), Whakamārama (Bay of Plenty), Woodend (Canterbury), Christchurch Airport, Leeston (Canterbury), Akaroa (Canterbury) and Campbell Island.

The warmest main centre over winter was Auckland with a mean temperature of 11.9C, 0.2C above average. Dunedin was the most unseasonably warm, however, 1.2C above average at 8.5C - the warmest winter the southern city has ever experienced.

Purerua, Northland and the South Island’s Westport had their hottest-ever winter maximums - 20.7C in Purerua and 20.3C in Westport.

The highest temperature recorded nationwide was in Whakatu (Hawke’s Bay), which reached 24C on June 2. The lowest was a chilly -10.6C at Otago’s Tara Hills on June 10.

The year 2022 contained New Zealand’s warmest and wettest winter on record.