New Zealand Climate Summary: May 2018 Issued: 6 June 2018
Warm and dry to start, followed by cooler and unsettled condi-tions
Temperature May temperatures were well above average (> +1.20°C) in parts of Hawke’s Bay. Temperatures were above average
(+0.51°C to +1.20°C) for most remaining parts of the North Island, except Northland, Taranaki and Wellington where
temperatures were near average (-0.50°C to +0.50°C). May temperatures were above average in Nelson and coastal
Canterbury north of Ashburton, and below average (-0.51°C to -1.20°C) in parts of Southland. Rainfall Rainfall was well below normal (< 50%) for coastal south Canterbury and north Otago. Below normal rain-fall (50-79%) was recorded in the western Bay of
Plenty, Hawke’s Bay, Wairarapa and eastern Otago. Rainfall was well above normal (>149%) for parts of the eastern Bay
of Plenty, Taranaki, Manawatu, Marlborough, and Kaikoura. Above normal rainfall (120-149%) was observed in parts of
Waikato, Whanganui, and north Canterbury. Soil Moisture As at 1 June 2018, soil moisture levels were above normal for the time of year for eastern and inland parts of the South
Island north of Southland, and southwestern parts of the North Island. Soil moisture levels were generally near normal
for the time of year across the re-mainder of the country.
Overall, mean sea level air pressures were much lower than normal over and to the south of New Zea-land during May. The
first half of the month was relatively warm and dry throughout the country. How-ever, during the second half of May, a
blocking anticyclone became established over the southeast of Australia. This delivered a prolonged period of disturbed
west and southwesterly winds over the country. Many fronts were embedded in this flow, which resulted in an unsettled
spell of weather with bands of thunderstorms passing over the country (see Highlights and extreme events section for further details). A weak ridge of high pressure covered the lower South Island during the final days of May,
bring-ing heavy frosts to parts of Central Otago, Southland, and the Mackenzie Basin.
The nationwide average temperature in May 2018 was 11.2°C (0.4°C above the 1981-2010 May aver-age from NIWA’s seven
station temperature series which begins in 1909).
• The highest temperature was 24.5°C, observed at Wairoa on 16 May.
• The lowest temperature was -8.8°C, observed at Mt Cook Airport on 31 May.
• The highest 1-day rainfall was 152 mm, recorded at North Egmont on 11 May.
• The highest wind gust was 187 km/hr, observed at Akitio on 21 May.
• Of the six main centres in May 2018, Auckland was the warmest, Tauranga was the sunniest, Dunedin was the coldest and
driest, Hamilton was the wettest, and Wellington was the least sunny.
• Of the available, regularly reporting sunshine observation sites, the sunniest four locations in 2018 so far (1
January – 31 May) were Wider Nelson (1069 hours), Marlborough (1068 hours), Hawke’s Bay (1042 hours) and Canterbury
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