Climate Summary for September 2015

A wet end to the month for eastern North Island.

Overview

Overall, September 2015 was characterised by air pressures that were higher than normal over the South Island and southwest of New Zealand, and lower than normal to the south and east of the country.  This circulation pattern resulted in more south-easterly airflows than normal over New Zealand.

The prevalence of south-easterly winds throughout September was certainly reflected in monthly rainfall totals with many coastal eastern areas receiving well above normal rainfall (>149% of September normal) for the month as a whole. These areas include the Bay of Plenty, Gisborne, Hawke’s Bay, eastern Manawatu-Wanganui, eastern Marlborough and northern Canterbury. Conversely, areas west of the Divide were sheltered from the moist airflow and as a result experienced an unusually dry month. Taranaki, western Manawatu-Wanganui, Tasman, Westland, Southland and Otago received below normal rainfall (50-79% of the September normal) with pockets of well below normal rainfall (< 50% of the September normal) recorded in some of these regions. Rainfall in the Auckland region and northern Waikato was near normal (80-119%).

As of 1 October 2015, soils remained notably drier than normal in coastal Hurunui, South Canterbury and northern Otago. The high rainfall in eastern areas observed over the past month helped to alleviate some of the dryness in soils, which are now wetter than normal in coastal Hawke’s Bay and Gisborne as well as in the district of Kaikoura. Elsewhere, soil moisture levels were typically near normal for this time of year.

September saw spring get off to a cool start allowing a number of ski fields around the country to extend their season. Temperatures were below average (0.51°C to 1.20°C below the September average) for virtually the entire South Island with the exception of coastal Westland and western Southland where near average temperatures (between -0.50°C to +0.50°C of the September average) were recorded. North Island temperatures were likewise largely below average with only parts of Northland, Auckland and northern Waikato escaping the brunt of the cold and recording near average temperatures (between -0.50°C to +0.50°C of the September average). The nation-wide average temperature in September 2015 was 9.8°C (0.9°C cooler than the 1981-2010 September average from NIWA’s seven station temperature series which begins in 1909)^[1].

Sunshine hours during September were largely in the near normal range (90-109% of the September normal) across the country. Despite high rainfall amounts for eastern areas of New Zealand, sunshine hours in these areas during the month of September were in fact near normal (90-109% of the September normal) reflecting the high intensity but short duration nature of the rain that fell. Above normal sunshine (110-125% of the September normal) was recorded across Nelson, Tasman and Westland.

Further Highlights:

• The highest temperature was 25.7°C, observed at Christchurch (Riccarton) on 16 September.
• The lowest temperature was -7.0°C, observed at Hanmer Forest on 8 September.
• The highest 1-day rainfall was 135.4 mm, recorded at Tutira (Hawke’s Bay) on 20 September.
• The highest wind gust was 167 km/hr, observed at Cape Turnagain on 4 September.
• Of the six main centres in September 2015, Auckland was the warmest and cloudiest, Christchurch was the coolest, Dunedin was the driest, Hamilton was the wettest and Wellington was the sunniest
• Of the available, regularly reporting sunshine observation sites, the sunniest four locations so far in 2015 (1 January to 30 September) are: Blenheim (1968 hours), Whakatane (1935 hours), Appleby (1925 hours) and Waipara West (1862 hours). 

Download the full Climate Summary for September 2015 [593KB PDF]

Climate Statistics for September 2015 [74 KB]

Contact

For further information, please contact:

Mr Chris Brandolino
NIWA Forecaster – NIWA National Climate Centre
Tel. 09 375 6335, Mobile (027) 886 0014