Climate Summary for August 2015

A cool month in the south and dry in the east.

Overview

Overall, August 2015 was characterised by air pressures that were much lower than normal to the west and south of the country, and pressures that were higher than normal to the north of New Zealand. This circulation pattern resulted in more northwest winds than usual over the country.

The northwest flow brought thunderstorms to parts of the country throughout the month, but were interrupted by outbreaks of cold southerlies that delivered snowfalls to low elevations that frequently closed highways in the South Island.  There were a number of extreme events as expected for this time of year (see Highlights and extreme events section for further details).

Rainfall anomalies varied across the country in August, with areas of higher and lower than normal rainfall sometimes in quite close proximity. However in general, areas in the west had higher rainfall than normal and areas in the east had lower rainfall than normal for August. Rainfall was above normal (120-149% of August normal) or well above normal (> 149% of August normal) in the west of the North Island, between Taupo and Gisborne, the coastal fringes of the West Coast, and southern Southland. In contrast, rainfall was below normal (50-79% of August normal) or well below normal (< 50% of August normal) in the eastern Bay of Plenty, southern Hawke’s Bay, Nelson, Marlborough, Kaikoura, Hurunui, and central Otago. The low rainfall in north Canterbury exacerbated concerns about the persistent dry conditions there. Near normal rainfall (80-119% of August normal) was experienced elsewhere in New Zealand. As of 1 September 2015, soils were notably drier than normal for Hawke’s Bay, coastal Wairarapa, eastern parts of Marlborough, north Canterbury, coastal south Canterbury and parts of Otago. Elsewhere, soil moisture levels were typically near normal for this time of year.

It was a cool month for most of the South Island and parts of the North Island. Mean temperatures were below average (0.51°C to 1.20°C below the August average) in parts of Auckland, western Waikato, Tararua, Tasman, south Canterbury, coastal Otago and Southland. Some locations in south Canterbury and Southland recorded well below normal temperatures for August (< 1.2°C below normal). Mean temperatures were near average for the remainder of the country (between -0.50°C to +0.50°C of the August average). The nation-wide average temperature in August 2015 was 8.6°C (0.2°C below the 1981-2010 August average from NIWA’s seven station temperature series which begins in 1909)^[1].

Sunshine was near normal (90-109% of the August normal) for much of the country in August. Exceptions were south-west Waikato which received above normal sunshine (110-125% of the August normal) and from Taranaki to Wellington as well as Nelson and Tasman that received below normal sunshine for August (75-89% of August normal).

Further Highlights:

• The highest temperature was 23.8°C, observed at Christchurch (Riccarton) on 3 August.
• The lowest temperature was -11.5°C, observed at Lake Tekapo on 11 August.
• The highest 1-day rainfall was 134 mm, recorded at North Egmont on 5 August.
• The highest wind gust was 141 km/hr, observed at Cape Turnagain on 19 August.
• Of the six main centres in August 2015, Auckland was the warmest and wettest, Dunedin was the coolest and cloudiest, Christchurch was the driest, and Hamilton was the sunniest.
• Of the available, regularly reporting sunshine observation sites, the sunniest four stations so far in 2015 (1 January to 31 August) are: Blenheim (1742 hours), Whakatane (1724 hours), Appleby (1701 hours) and Waipara West (1671 hours).

Download the full report:

Montly Climate Summary for August 2015 [496 KB]

Climate Statistics for August 2015 [74 KB]

For further information, please contact:

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