Climate Summary for September 2010

Wet and wild westerlies

  • Rainfall:  Double normal rainfall in the southwest of North Island, the north and northwest of South Island, and around Invercargill.  Many September rainfall records broken in these areas.  Very wet in most other regions, but dry in south Canterbury and coastal Gisborne.
  • Temperatures: Above average in the north and east of the North Island, and the eastern South Island. Well below average in the west and south of the South Island.
  • Sunshine: Well below normal sunshine hours in western areas of both islands.

September 2010 was characterised by extremely low pressures over New Zealand, bringing wild westerly winds.  The effect of the stronger-than-normal westerly winds during September was very clear – rainfall was record high or well above average, and sunshine hours were well below average, in western areas of both islands.  It was also much cooler than usual in the west and south of the South Island, but warmer than average in eastern areas; both are trademarks of enhanced westerly circulation.

September rainfall was more than double normal (at least 200 percent) in the southwest of the North Island, from Turangi to Taranaki to the Kapiti Coast, as well as the north and northwest of the South Island – including Nelson, Blenheim and Buller – and around Invercargill.  Many locations in these areas experienced their wettest September on record.  Most other regions around the country also received above normal rainfall (between 120 and 150 percent of normal).  The only exceptions were eastern Northland and coastal north Canterbury (which experienced near normal rainfall), and Gisborne and south Canterbury (which received less than 50 percent of usual September falls).

Extremely warm temperatures affected the country at both the start and end of the month – but an intense southwesterly event from the 17th until 24th brought snow to very low levels in the far south, and record low temperatures there.  Overall, monthly mean temperatures were above average (between 0.5°C and 1.2°C above average) in eastern regions of both islands, as well as from Taranaki down to Wellington.  In contrast, much of the west and south of the South Island experienced below average temperatures (1.2°C to 0.5°C below average).  The New Zealand national average temperature was 10.9°C (0.5°C above the 1971–2000 September average).   

Well below average sunshine totals (less than 75 percent of normal) were recorded in western areas of both islands, due to the stronger-than-normal westerly winds during September.  In contrast, above normal sunshine hours were received in south Canterbury (between 110 and 125 percent of normal).  In most other regions, September sunshine totals were closer to normal (ranging between 90 and 110 percent of normal).

Further Highlights:

  • The highest temperature was 24.6°C, recorded at Kaikoura on the 6th (near record).
  • The lowest temperature was -6.2°C, recorded at Lake Tekapo on the 22nd.
  • The highest 1-day rainfall was 135.0 mm recorded at Milford Sound on the 5th.
  • The highest wind gust was 204 km/hr, recorded at Cape Turnagain on the 23rd.
  • Of the six main centres, Tauranga was the warmest, Dunedin the coolest, Christchurch the sunniest and driest, and Wellington the wettest.

Full report

Full details of the  September 2010 Climate Summary

Climate statistics table

Climate statistics for PDF File September 2010

For further information, please contact:

Ms Georgina Griffiths – Climate Scientist– NIWA National Climate Centre, Auckland, Tel. (09) 375 4506 (work) or (027) 2936545 (mobile); or

Dr Andrew Tait – Climate Scientist – NIWA National Climate Centre, Wellington, Tel.  (04) 386 0562 (work) or (027) 327 7948 (mobile)