Niwa climate scientist Gregor Macara said winter 2023 began on a warm note, as New Zealand observed its fifth-warmest June and fourth-warmest July on record.
In contrast, August recorded below-average temperatures, making New Zealand’s overall winter temperatures the fifth-warmest on record.
But for Dunedin, it was the warmest winter since records began in 1947, with a mean air temperature of 8.5°C — 1.2°C above normal.
Waimate (7.7°C) had its second-warmest winter on record, and Oamaru (7.7°C), Oban (Stewart Island, 7.7°C) and Nugget Point (7.4°C) had their third-warmest winters.
Elsewhere, temperatures were above average for western parts of Southland and coastal Otago, and generally near average for the remainder of the country.
Mr Macara said high pressure systems delivered frequent frosts to much of the South Island during June.
In addition, an inversion layer became established over inland parts of the South Island between June 6 and 25, causing cold air to pool in valleys and basins.
"This contributed to relatively low daily maximum and minimum temperatures in several locations.
"Particularly notable was Lauder, where the air temperature remained below freezing for nearly five days — from 7pm on June 6, to 1pm on June 11.
"On June 10, Lauder’s maximum temperature was only -2.7°C."
A considerable reduction in the number of rain-bearing storms arriving from the north of New Zealand meant it was a relatively dry season for many parts of the country, Mr Macara said.
Mean sea level air pressure was also lower than normal to the east of the North Island during winter overall, resulting in slightly more southerly airflows than usual.
"These air pressure and wind patterns were influenced by a decaying La Niña at the start of winter, and a developing El Niño by the end of the season."
Fifteen locations observed record or near-record low winter rainfall totals, he said.
Among them was Franz Josef, which had its driest winter on record with just 463mm of rain.
It was also relatively dry at Mt Cook Airport, where winter rainfall was 39% of normal.
"This lack of precipitation was reflected in snow depths measured around the southern regions.
"Both Mount Hutt [Canterbury] and Coronet Peak [Otago] were forced to temporarily close in June, with a lack of suitable weather for either natural or artificial snow production."
In inland Otago, rainfall was below normal during winter, but above normal or well above normal in southern parts of Southland and eastern Otago.
Soil moisture at the end of winter was near normal for most of the country, but above normal in isolated areas inland of Dunedin.
