Niwa National Climate Centre
Tuesday 8 September 2009

National Climate Summary – Winter 2009: Extreme temperature swings through winter

• Temperature: Near average in many regions; after a cold start to winter, a record warm August.
• Rainfall: Well above normal in Bay of Plenty, Gisborne, and Westland. Below normal in the east of the South Island and parts of Wellington, Kapiti Coast and the Wairarapa. Near normal elsewhere.
• Sunshine: A sunny winter for the north and west of the North Island, as well as in the Clutha, and parts of Canterbury and Westland. Rather cloudy in Buller.

The temperature averaged over the whole winter was close to average for much of New Zealand, with the three-month nationally-averaged temperature of 8.3°C being only 0.2°C above the winter mean. However, extreme temperature swings were observed through winter; June and July were colder than normal, followed by a record warm August.

Winter rainfall totals were well above normal (between 120 and 150 percent of normal) in the Bay of Plenty, Gisborne, and Westland. In contrast, winter rainfalls were below normal (between 50 and 80 percent of normal) throughout the east of the South Island, as well as in parts of Wellington, Kapiti Coast and the Wairarapa. Rainfalls were near normal elsewhere.

June 2009 was dominated by higher-than-normal pressures over the country, resulting in more frosts and much colder than normal temperatures everywhere. During July 2009, there was a transition towards more southwesterly winds over New Zealand. During August 2009, frequent northerly winds affected the country, resulting in very warm temperatures.

Major Highlights:

• 16 - 26 June: Freezing southerly conditions brought snow and ice to low levels in Otago and Southland on the 16th. Frosty conditions and very cold temperatures then affected many areas until the 26th.
• 27 - 30 June: A slow-moving low to the north of New Zealand brought heavy rain, strong winds and thunderstorms to the northeast of the country, as well as snow to the Central Plateau. A civil defence emergency was put in place in Gisborne on the 30th, as rain continued and rivers rose.
• 23 - 24 July: A powerful storm brought damaging winds to Wellington and much of the east coast of the North Island (cutting power to over 4,000 people), and heavy rain to Wellington, the Wairarapa and Greymouth, causing road and rail closures, slips and flooding in these areas.
• 26 - 31 August: Thunderstorms brought heavy rain and lightning to Taranaki, Auckland and the western Bay of Plenty (cutting power to more than 8000 homes). Heavy rain on the 31st resulted in surface flooding across the greater Wellington region.
• The lowest temperature during winter was recorded at Middlemarch, with a minimum temperature of -11.7°C on July 19th. The highest temperature for winter was 22.2 °C recorded at Timaru on August 25th. The highest 1-day rainfall was 205 mm, recorded at Te Puia Springs (Gisborne) on June 29th.
• Of the six main centres, Auckland was the warmest, Christchurch the coldest, Tauranga the wettest but also the sunniest, and Dunedin was the driest.

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