National Climate Centre Friday 2 September 2011

National Climate Centre Friday 2 September 2011

National Climate Summary – August 2011: Snow & sunshine - very dry in north & west

• Precipitation: Polar outbreak mid-month produced heavy snow across eastern and alpine areas of the South Island, as well as Wellington. Snow also fell across the lower North Island, with flurries in unusual locations further north. But overall, August was extremely dry for western, northern and alpine areas of the South Island, as well as for Taupo northwards.

• Sunshine: Extremely sunny across alpine and northern South Island, as well as Central Plateau, Bay of Plenty, Waikato, Gisborne and Hawkes Bay. Rather sunny in all other regions, excepting Wanganui, Kapiti, and Wellington.

• Temperatures: Well below average or below average across much of the North Island, as well as for the northwest, north and east of South Island. Near average in Southland, Fiordland, southern Westland and the Lakes District.

August 2011 was characterised by frequent southerly winds, and higher pressures than usual, over New Zealand. A polar outbreak affected New Zealand mid-month, bringing heavy snow to unusually low levels across eastern and alpine areas of the South Island, as well as Wellington. Snow also fell across the lower North Island, with flurries in unusual locations further north. The long-lived southerly winds between August 14 and 17 delivered extremely cold air over the country. Numerous August low temperature records were broken between the 14th and 17th. Anticyclones (highs) then prevailed over New Zealand between August 19 and 24, resulting in extremely icy or frosty mornings. The last week of the month was mostly dry and sunny in many regions, with some unusually warm and ‘spring-like’ temperatures experienced.

While the southerly winds brought precipitation (rain, snow, or sleet) to eastern areas of both Islands, the remainder of the country stayed extremely dry overall, due to the dominance of anticyclones (highs) during the month. August precipitation was mostly well below average (less than 50 percent of August normal) for western, northern and alpine areas of the South Island, as well as for Taupo northwards. It was the driest August on record in the Waikato, and in and around Nelson. Rainfall was near normal (between 80 and 119 percent of normal) between Wanganui and Hawera, in coastal Southland, and along the east coasts of both Islands, as well as for Wellington. Locally, there were small areas of above normal precipitation in the east (Wairarapa, Kaikoura coast, near Ashburton, and north Otago).

Sunshine totals were well above normal for alpine and northern areas of the South Island, as well as for the Central Plateau, Bay of Plenty, Waikato, Gisborne and Hawkes Bay. It was the sunniest August on record for Te Kuiti, Nelson, Takaka, Blenheim and Lake Tekapo. It was also a rather sunny for the remainder of the country, with sunshine totals between 110 and 124 percent of August normal. The only exceptions were Wanganui, Kapiti coast, and Wellington, which experienced near normal August sunshine.

Anticyclones during August and the mid-month polar outbreak meant that monthly minimum temperatures were below average or well below average across the entire North Island, as well as the northwest, north and east of the South Island. However, maximum temperatures were elevated in some areas sheltered from the prevailing southerly winds. The average temperature in August 2011 was 8.2°C (0.5°C below the 1971–2000 August average) using NIWA’s seven-station temperature series which begins in 1909 .

Further Highlights:

• The highest temperature was 22.1°C, observed at both Whangarei and Cheviot on 30 August.

• The lowest temperature recorded was -10.1°C at Lake Rotoiti (Nelson Lakes) on 16 August.

• The highest 1-day rainfall experienced was 76.2 mm recorded at Milford Sound on 26 August.

• The highest gust was 167 km/hr observed at Cape Turnagain on 7 August.

• Of the six main centres in August 2011, Auckland was the warmest, Christchurch the coldest, Tauranga the sunniest, Wellington the wettest, and Auckland and Hamilton jointly the driest.

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