NIWA

Climate Summary for May 2011

25 July 2011

Warmest May on record.

Temperatures: Warmest May since records began in 1909. Temperatures more than 2°C above May average between Waikato and Christchurch, and in the Lakes District.
Rainfall: A record wet May for Nelson. Extremely wet for much of the North Island, as well as the Tasman District, Marlborough, Otago and south Canterbury.
Sunshine: Very cloudy for the South Island and southwest of the North Island.

It was the warmest May on record, using NIWA's seven-station temperature series which began in 1909. The average temperature for May was 12.9°C (2.2°C above the 1971–2000 May average). The previous record-holder from this series was May 2007 (with an average temperature of 12.5°C, or 1.8°C above the 1971–2000 May average). Monthly mean temperatures for May were at least 2°C above May average between the Waikato and Christchurch, as well as in the South Island Lakes District, with many records broken. For the remainder of the country, monthly mean temperatures were also well above average (between 1.2°C and 2°C above May average).

New Zealand was affected by more northerly winds than usual during May, squeezed between low pressures over the Tasman Sea and anticyclones ('highs') parked east of the country. These northerly winds contributed to the record-breaking May warmth, a record wet May for Nelson, and extremely high rainfall totals for many regions of the North Island (with at least 120 percent of normal May rainfall), as well as for Marlborough, the Tasman District, Otago and south Canterbury. In contrast, southern Hawkes Bay, the Wairarapa, and Banks Peninsula experienced a very dry May (with rainfall about half of normal), and rainfall was below normal (between 50 and 79 percent of normal) in parts of Fiordland.

Overall, May was a month of extremes. May started with a heat wave on the West Coast of the South Island; on the 1st of the month, 26.7°C was observed at Hokitika and 25.0°C at Westport (both new May records). A tornado swept through Albany (Auckland) on the 3rd. Flooding rains affected Otago on May 7/8, and Nelson and Takaka on May 25/26.

Sunshine totals in May were below normal (between 75 and 90 percent of normal) for much of the South Island, and from Taranaki to Wellington. It was the cloudiest May on record for Hokitika, Cromwell and Stratford. In contrast, sunshine totals were above normal (between 110 and 125 percent of May normal) on the east coast of the North Island, and in parts of Northland. Elsewhere, totals were close to normal (between 90 and 110 percent of May normal).

Further Highlights:

The highest temperature recorded was 26.7°C at Hokitika on the 1st (a new May record there).
The lowest temperature recorded was -4.8°C at Pukaki Aerodrome on the 29th.
The highest 1-day rainfall of 289 mm was recorded at North Egmont on the 25th.
The highest gust was 184 km/hr recorded at Southwest Cape on the 12th.
Of the six main centres, Auckland was the wettest but also the warmest, Tauranga was the sunniest, and Christchurch was the driest.