Near record rainfall, snow and record low temperatures marked September as a miserable month for many parts of the country, a monthly climate summary has found.

NIWA's national climate centre said many areas including Taranaki, Turangi and the Kapiti Coast in the North Island, and Nelson, Blenheim, Buller and Invercargill in the South, saw at least double the normal amount of rainfall.

The heavy rain caused widespread flooding, road closures, and slips and forced some schools to close their doors.

Other areas, such as Tauranga, received between 20 and 50 per cent more rain than average in September, while Gisborne and south Canterbury had a drier month with less than 50 per cent of the usual amount of rain.

NIWA said the well above average rainfall was an effect of extremely low pressures, bringing stronger-than-normal westerly winds.

"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."

Sunshine hours were well below average at 75 per cent of normal in western areas of both islands, while higher in south Canterbury.

Though extremely warm temperatures affected the country at the beginning and end of the month, NIWA said an "intense" southwesterly from September 17 to 24 brought snow and record low temperatures to the far south, which caused the Stadium Southland roof to collapse in Invercargill.

It was estimated that farmers face more than $50 million in losses, after losing about 500,000 lambs and having a 20 to 25 per cent drop in milk collection due to the heavy snow.

"Overall, monthly mean temperatures were 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."

The New Zealand national average temperature was 10.9degC, 0.5degC above the 1971 to 2000 September average.

Other climate highlights:

* Highest temperature recorded was 24.6degC at Kaikoura on September 6;

* Lowest temperature recorded was -6.2degC at Lake Tekapo;

* Highest one-day rainfall was 135mm at Milford Sound on September 5;

* The highest wind gust was 204km/hr at Cape Turnagain on September 23;

* and of the six main centres, Tauranga was the warmest, Dunedin the coolest, Christchurch the driest, and Wellington the wettest.