Autumn 2008

Autumn 2008: a season of extremes – heatwaves, drought, floods and frost.

• Rainfall: Well below normal in alpine areas and the west and south of the South Island
• Soil moisture: Significant deficits in western areas of the North Island
• Temperature: Above average in the north and west, below average in Otago
• Sunshine: Well above normal in west and south of the South Island

Low rainfall occurred in the alpine areas and west of the South Island, with one of the driest autumn’s on record. It was very dry and sunny in the west and south of the South Island and Manawatu. Mean autumn air temperatures were above average in the north and west of both islands, but below average in Otago. The national average temperature of 13.3 °C was exactly average for autumn. But in the South Island unusual in March, and May brought extended periods of frost. It was extremely sunny in the west and south of the South Island.

Rainfall was about 50 percent (half) of normal in alpine areas and in South Westland, Fiordland, and less than a quarter of normal in Timaru. Unusually, significant soil moisture deficits (at least 110 mm) persisted until the end of March in many western North Island areas, dramatically affecting dairy production. Seven people drowned in a river flood in April, whilst May was unusually windless and extremely dry in many South Island places. The overall autumn climate pattern was dominated by more anticyclones to the south and southeast of the South Island, and depressions northwest of the North Island, producing more easterlies and northeasterlies.

Major highlights

• The highest temperature during autumn 2008 was 34.8 ºC recorded at both Timaru Airport, and 35°C (rounded to the nearest degree) at Culverden and Woodbury on March 19th. This was 1°C less than the highest ever New Zealand March temperature of 36°C recorded at Ashburton in 1956. Heatwave conditions occurred from 18-21 March in inland and eastern South Island areas, with temperatures of 30°C or more, and many locations recording their highest March temperatures on record.
• The lowest air temperature during the month was -7.7ºC recorded at Albert Burn in Central Otago on May 5^th under clear skies. It was much frostier than normal in May, with ground frosts of 5°C or more occurring on 24 days in some inland areas.
• April produced several high rainfall/flood-producing events – the worst being that of 14-16 April with 132 mm in 24 hours in Takaka on 14 April, 126 mm at Matamata, 108 mm at Rotorua and 101 mm at Taupo on the 15^th – the deluge caused flooding of homes in Rotorua, and a river flood on the Mangetopopo drowning seven people, and earlier in the day a man was struck by lightning and killed near Dargaville. On 29 and 30 April 40 mm at Paraparaumu, 95 mm at North Egmont, and 94 mm in Wellington caused flooding in the Okato, the Kapiti Coast and Wellington.
• By 29^th March severe and significant soil moisture deficits (more than 130 and 110 mm) were present in throughout the west of the North Island from Auckland to the Manawatu, east of North Island, and the east of the South Island. The combination of the hot and dry conditions meant that dairy farmers continued drying off dairy stock, with sheep farmers selling stock early. April rainfall ended the severe and significant soil moisture deficits.
• Of the five main centres, Auckland was easily the warmest, Wellington by far the wettest, Hamilton the sunniest and Christchurch the driest. Autumn temperatures were above average in Hamilton and Wellington, and below average in Christchurch. Rainfall was well above normal in Wellington, near normal in Auckland, and below normal in the three other centres. Autumn sunshine was near normal in Auckland and Christchurch, and above normal in Hamilton, Wellington and Dunedin.

Rainfall

Autumn rainfall was about 50 percent (half) of normal in alpine areas and south Westland, Fiordland, and less than a quarter of normal around Timaru. Cape Reinga record almost 200 percent (double) normal rainfall, and 150 percent (one and a half times) normal rainfall occurred in eastern Bay of Plenty, parts of the east of the North Island and Wellington.

Temperature

Seasonal mean temperatures were about 0.5 °C above average throughout the north and west of both islands. They were closer to average in other North Island areas, and below average but about 0.5°C in Marlborough, Canterbury and Central Otago.

Sunshine

Autumn sunshine hours and/or solar radiation were at least 110 percent of normal in the southwest of the North Island, the west, south and alpine areas of the South Island. Southern and alpine areas received totals in excess of 120 percent of normal. Only in Gisborne were totals less, being 90 percent of normal.

Full report

• Autumn 2008 climate summary (PDF 66 KB)

For further information, please contact:

Dr Jim Salinger – Principal Scientist, Climate NIWA National Climate Centre – Auckland Phone +64 9 375 2053 [email protected]

Stuart Burgess – Climatologist NIWA National Climate Centre – Wellington Phone +64 4 386 0569 [email protected]

Geoff Baird – Communications Manager Phone +64 4 386 0543 [email protected]

Acknowledgement of NIWA as the source is required.