Earth Sciences New Zealand meteorologist Chester Lampkin said a sudden stratospheric warming (SSW) event that occurred in September, had a large impact on October’s weather across the southern regions.
"Displaced air masses from the SSW event led to mean sea level air pressure that was lower than normal across both the North and South Island of New Zealand, with the strongest negative anomaly across the South Island.
"This pressure gradient led to strong westerlies across the whole of New Zealand — the result was a wet and unsettled month, with multiple severe gale wind events in the east and south of the South Island.
"Of particular note was a wind event and storm system on October 23, that caused widespread wind damage to parts of the South Island and broke several temperature records for October."
Three Otago locations also recorded their wettest October on record.
Tara Hills recorded 142mm of rain for the month (more than three times its normal rain), Ranfurly had 102mm and Cromwell had 91mm (both more than 2.5 times the normal amount).
Milford Sound (1313mm), Manapouri West Arm (882mm), Five Rivers (147mm), Lauder (99mm) and Clyde (88mm) all recorded their second-highest October rainfall totals.
The highest one-day rainfall for the country was 226mm, recorded at Milford Sound on October 20.
Rainfall was well above normal for most of Southland and Otago for the month, leaving soil moisture higher than normal at the end of October.
Mr Lampkin said the October 23 storm also brought "violent" winds to much of Otago and Southland, causing major damage.
Uprooted trees, lifted roofs and downed power lines prompted a state of emergency to be declared in Southland and Clutha.
October wind gust records were broken in Dunedin (Musselburgh) (119kmh), Manapouri (102kmh), Gore (124kmh) and South West Cape (194kmh); Invercargill (137kmh) had its second-highest, and Tara Hills (100kmh), Ranfurly (92kmh), Middlemarch (114kmh) and Tiwai Point (147kmh) recorded their third-highest October wind gusts.
Overall, October was warmer than average again for most of New Zealand, including Oamaru, where regular and long warm spells from foehn wind events pushed the North Otago town to its second-highest October mean maximum air temperature of 17.6°C (2.2°C warmer than normal).
However, temperatures were below average in Fiordland, interior Otago and parts of lower Westland, and the remaining areas were near average, he said.
Nationwide, the average temperature for October 2025 was 13.1°C, making it New Zealand’s 10th warmest on record.
