Last month was the warmest May on record in New Zealand, according to NIWA.
All five of the warmest Mays since records began in 1909 have occurred since 2011.
The nationwide average temperature last month was 13.1C — 2.0C above the 1991-2020 May average.
The highest temperature was seen in Waiau on May 3, where temperatures reached 27C. The lowest temperature was seen in Middlemarch on May 16, where temperatures reached a chilly -5.2C.
The first eight days of May 2023 were also “exceptionally warm for the time of year”, with dozens of locations observing record or near-record high daily minimum and maximum temperatures during this period, according to NIWA’s May climate summary.
The warmth persisted for the month overall, and monthly temperatures were above average (0.51-1.20C above average) or well above average (>1.20C above average) in every region of New Zealand.
It was also the second warmest May for sea surface temperatures near the South Island since records began in 1981, after a marine heatwave delayed the seasonal transition to colder temperatures.
“The widespread nature of May’s exceptional warmth, both on land and in the sea, have been exacerbated by climate change,” NIWA said.
Meanwhile, rainfall was abundant for many parts of the country last month, with above normal (120-149% of normal) or well above normal (>149% of normal) totals seen in Northland, Auckland, Waikato, Bay of Plenty, Taranaki, parts of Manawatū-Whanganui, Wellington, Tasman, Nelson, northern Marlborough, West Coast, inland Otago and western Southland.
The wettest locations compared to normal were Kaikohe, Rotorua, and Motueka, which recorded 377%, 342%, and 206% of normal May rainfall, respectively. Meanwhile, rainfall was below normal (50-79% of normal) or well below normal in parts of Gisborne, Hawke’s Bay, much of Canterbury, and northern Otago.
It was particularly dry in Oamaru, where just 24mm of rainfall (32% of normal for May) was recorded.
The highest one-day rainfall was 241 mm, recorded at Milford Sound on May 2. The highest wind gust was 169 km/h, observed at Secretary Island on May 10, and South West Cape on May 26.
Fourth warmest autumn on record
This autumn was also the fourth warmest autumn on record, after 2022, 2016 and 1938.
The nationwide average temperature over the autumn period was 14.5C — 1.1C above the 1991-2020 average.
The highest temperature was 30.5C, which was observed in Akaroa on March 2. The lowest temperature was -5.2C, observed at Middlemarch on May 16.
In addition, 38 locations across the country saw their warmest or near-warmest autumn on record. Chatham Island had its warmest autumn since records began in 1878, while Napier had its second warmest autumn since 1870.
Much of the warmth was driven by very warm overnight temperatures, with 14 locations experiencing their warmest mean overnight temperature for autumn, NIWA said. This included Christchurch (Botanic Gardens), which saw its warmest mean overnight temperature for autumn since records began there in 1863.
Of the six main centres, Auckland was the warmest, while Christchurch was the coolest and driest. Tauranga was the wettest and sunniest, while Wellington was the least sunny.
The sunniest four locations so far this year are Taranaki (1101 hours), Central Otago (1100 hours), Mackenzie Basin (1096 hours) and the West Coast (1060 hours).