"As is often the case, October weather patterns were changeable.
"Periods of high pressure and calm weather were interspersed with unsettled and active weather.
"For the month as a whole, air pressure was higher than normal south and east of ... New Zealand, with lower than normal pressure in the western Tasman Sea.
"This atmospheric pattern was associated with more northerly and northeasterly air flows than normal over New Zealand."
Ms Fedaeff said the air flows brought frequent warm and humid conditions and were a key driver behind the warm month alongside warmer-than-normal coastal waters.
"Many locations experienced a record or near-record warm October, particularly when looking at overnight minimum temperatures."
Middlemarch (5.7degC), Dunedin at Musselburgh (9.1degC), Te Anau (6.3degC), Gore (7degC) and South West Cape (8.1degC) all recorded their highest overnight minimum temperatures.
Overall, the nationwide average temperature for October 2021 was 13.2degC (1.2degC above the 1981-2010 October average), making it New Zealand’s fifth-warmest October since records began in 1909.
In the southern region, Middlemarch (12degC) recorded its highest mean air temperature for October, and Milford Sound (11.8degC), Manapouri (West Arm) (10.4degC) and Lumsden (10.8degC) recorded their second-highest.
Manapouri (West Arm) (23degC) and South West Cape (21degC) also recorded their second-highest daily maximum air temperatures for October.
The warmth for the month as a whole occurred despite occasional cold snaps, she said.
Rainfall patterns across the country were mixed.
It was above normal (120%-149% of normal) in North Otago, but dry conditions were observed during October in Fiordland and much of Southland.
Tiwai Point experienced its third-lowest October rainfall total since records began in 1970.
The highest October temperature recorded in New Zealand last month was 28.9degC in Napier on October 27, and the lowest was -4.1degC at Mt Cook Airport on October 14.
The highest one-day rainfall was 151mm, recorded at Arthurs Pass on October 17, and the highest wind gust was 156kmh at Cape Turnagain on October 19.
