National Climate Summary – September 2011: Dry, sunny & cool

National Climate Summary – September 2011: Dry, sunny and cool start to spring

• Rainfall: Less than half of normal in Bay of Plenty, Gisborne, the West Coast, and Mackenzie country. Generally dry elsewhere, except for Auckland, central Otago and coastal Southland. Driest September on record for Whakatane.
• Sunshine: Extremely sunny for North Island, and north and east of South Island.
• Temperatures: Below average over North Island, also for Nelson, Marlborough, West Coast, Coastal Fiordland, south Canterbury. Near average elsewhere.
• Soil moisture: Already below normal for this time of year in north Canterbury, Mackenzie country and central Otago, as well as parts of the North Island.

September 2011 was characterised by higher pressures than usual over the Tasman Sea and lower pressures to the south and east of the country. This pressure pattern produced more southwest winds than normal over New Zealand.

It was a very dry month for most regions. Less than half of normal September rainfall was recorded in Bay of Plenty, Gisborne, on the West Coast, and in the Mackenzie country. It was the driest September on record for Whakatane. It was generally very dry elsewhere, with below normal rainfall (between 50 and 79 percent of September normal). The only exceptions were coastal Southland (where rainfall totals between 120 and 149 percent of September normal were recorded), and Central Otago and Auckland (where near normal rainfall was experienced). Soil moisture levels are already below normal for this time of year in north Canterbury, Mackenzie country and central Otago, as well as parts of the North Island.

September sunshine totals were well above normal (more than 125 percent of normal) across much of the North Island, and the north and east of the South Island. It was the sunniest September on record for Dargaville, New Plymouth, Tauranga, Dannevirke, Gisborne, Waipawa, Takaka, and Cheviot. For the remainder of the country, it was also a rather sunny September (with sunshine totals between 110 and 125 percent of normal). The only exceptions were Fiordland and Southland, which experienced close to normal September sunshine hours.

Mean temperatures well below average (between 1.2°C and 0.5°C below September average) across much of the North Island (with the exceptions of Coromandel, and parts of Auckland, Taranaki and Wanganui, where near average temperatures were recorded), as well as for most of Nelson and Marlborough, along the West Coast, coastal Fiordland, and south Canterbury. In north Canterbury, Southland and Otago, temperatures were close to average (within 0.5°C of September average).

The average temperature in September 2011 was 9.7°C (0.7°C below the 1971–2000 September average) using NIWA’s seven-station temperature series which begins in 1909.

Further Highlights:
• The highest temperature was 22.3°C, observed at Hanmer Forest on 30 September.
• The lowest temperature recorded was -6.1°C at Pukaki Aerodrome on 14 September.
• The highest 1-day rainfall experienced was 98 mm recorded at Milford Sound on 10 September.
• The highest gust recorded was 126 km/hr at Castlepoint on 1 September.
• Of the six main centres in September 2011, Auckland was the warmest and wettest, Christchurch the coldest and driest, and Tauranga the sunniest.

Please see the attached full summary (pdf)

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