Niwa climate scientist Gregor Macara said the mean temperature at the Musselburgh weather station was 8.5°C — the highest July average temperature since records began in 1947.
Waipounamu (northwest of Gore) also recorded its highest average with 5.7°C.
Waimate (7.7°C), Five Rivers (6°C), Cromwell (5.8°C), Alexandra (5.6°C) and Balclutha (6.6°C) recorded their second-highest July mean temperatures.
Temperatures on July 18 and 24, were particularly warm when a northerly airflow crossed New Zealand, contributing to some of the highest July daily temperatures on record.
The highest July temperature in New Zealand was 21.1°C, observed at Wairoa on July 18.
Middlemarch (18.4°C) and Cromwell (18.7°C) recorded their highest July day temperatures, and Clyde (19°C) and Oban (16°C) recorded their equal-highest.
Mr Macara said sea surface temperatures near New Zealand remained higher than average, and marine heatwave conditions persisted in coastal waters near the South Island and lower North Island.
"It was a relatively warm July throughout New Zealand, with well above average or above average temperatures observed for most areas.
"Overall, the nationwide average temperature in July 2023 was 9.1°C.
"This was 1.1°C above the 1991-2020 July average, making it New Zealand’s fourth-warmest July since Niwa’s seven station temperature series began in 1909."
Despite the warmer-than-average readings, July was a wet month for eastern and southern parts of the South Island, he said.
Dunedin had the least amount of sunshine of New Zealand’s main centres and received 153% of its normal July rainfall.
Gore, in particular, had its wettest July day since records began in 1907, when 35mm fell on July 2.
"Rainfall was above normal or well above normal in eastern parts of Canterbury and Otago, and southern parts of Southland," he said.
"Rainfall was below normal or well below normal for northern Fiordland, inland Otago, much of the West Coast, Nelson, Marlborough and Tasman."
