NIWA records warmest May on record 'exacerbated by climate change'

May kicked off with the first eight days of the month being "exceptionally warm".
May kicked off with the first eight days of the month being "exceptionally warm". Photo credit: Getty Images

If May felt warmer than usual for that time of year, you weren't wrong because according to NIWA it was the warmest May on record.

Aotearoa's nationwide average temperature for the month of May, 2023 was 13.1C, that's 2C higher than the average from 1991 to 2020.  

In NIWA's Climate Summary for May, it said of the five warmest Mays on record, all have occurred since 2011.  

May kicked off with the first eight days of the month being "exceptionally warm" for that time of year, and NIWA says several locations saw record or near-record high daily maximum and minimum temperatures during the month. 

"The warmth persisted for the month overall, and monthly temperatures were above average (0.51-1.20°C above average) or well above average (>1.20°C above average) in every region of New Zealand."

For sea surface temperatures near the South Island, NIWA says it was the second warmest May on record where a marine heatwave delayed the season transition to cooler temperatures.

"The widespread nature of May’s exceptional warmth, both on land and in the sea, have been exacerbated by climate change." 

NIWA says the highest temperature for May was recorded in Waiau on May 3, at 27C, with the lowest recorded at Middlemarch on May 16, at -5.2C. 

And among the warmth was an "abundant" amount of rain for many parts of the motu. 

NIWA says many regions across the motu recorded above normal (120 to 140 percent) or well above normal (>149 percent of normal) totals were observed from Northland right down to western Southland. 

"The wettest location compared to normal were Kaikohe, Rotorua and Motueka, which recorded 377 percent, 342 percent and 206 percent of normal May rainfall, respectively."

On the other hand, rainfall was below normal (50 to 79 percent of normal) or well below normal (<50% of normal) in parts of Gisborne, Hawke's Bay, and much of Canterbury and northern Otago.

"It was particularly dry in Oamaru, where just 24mm of rainfall was recorded."

The highest one-day rainfall was 241mm which was recorded at Milford Sound on May 2.