NIWA

Summer 2010-11

3 March 2011

Heat waves and deluges.

Temperatures: Record or near-record high summer temperatures recorded at many locations in the North Island, as well as the north of the South Island. Above average temperatures elsewhere. Multiple heat waves during the summer.
Rainfall: Several deluge rainfall events during the summer, often associated with ex-tropical cyclones. Record or near-record high summer rainfall in parts of: Northland, Auckland, Coromandel, Bay of Plenty and Otago. A wet summer for many other regions.
Soil moisture deficits: Summer started with drought in Northland, Waikato and Ruapehu, but wet conditions in the northern North Island eased the situation. At the end of summer, significant deficits remain in southern Taranaki, Manawatu, Kapiti coast, Wellington, Wairarapa, Nelson, Marlborough and north Canterbury.

In Summer 2010/2011, there were more northeasterly winds over the North Island, and more northwest winds over the South Island, than is typical for the season overall. These northerly quarter winds ensured a very warm summer for all regions of the country, and several heat wave events. The summer was characterised by deluge rainfalls, often associated with ex-tropical cyclones or subtropical lows.

A severe storm passed over the country on December 27/28, resulting in significant rainfalls, flooding and gale force winds for many areas. During January, three lows of tropical origin brought torrential rain and gales; former tropical cyclones Vania and Zelia produced heavy rain on the 18th on the West Coast, resulting in the Fox River bursting its banks. A low of tropical origin (which formed near New Caledonia) moved towards New Zealand on January 22/23, producing extremely heavy rainfall, flooding, slips and road closures over much of the North Island, north of about Wanganui. Ex-tropical Cyclone Wilma moved rapidly across the northeastern North Island on January 28/29, causing widespread deluge rainfalls, severe flooding and slips in these regions. And lastly, record-breaking rainfall occurred in Otago on 6 February.

Summer mean temperatures were well above average (at least 1.2°C above average) for all of the North Island and in Nelson, Marlborough, north Canterbury and Buller, with records set at numerous locations. Elsewhere, seasonal temperatures were between 0.5°C and 1.2°C above average. Several heat wave events occurred during summer, namely 18 – 22 December, 27/28 December, 18/19 January and 2 – 7 February. The New Zealand national average temperature was 17.5°C (0.9°C above the 1971–2000 summer average).

It was an extremely wet summer for many regions of the country, with summer rainfall totals exceeding 120 percent of normal. Record or near-record high summer rainfalls were observed in parts of Northland, Auckland, Coromandel, Bay of Plenty and Otago. In contrast, Manawatu, Wellington, Wairarapa, Canterbury and Buller recorded closer to normal summer rainfall totals.

Further highlights:

The highest temperature recorded was 41.3°C recorded at Timaru (Gardens) on 6 February (a new all-time record at this site).
The lowest temperature was -2.3 °C, recorded at Tara Hills (South Canterbury) on 8 December (the 2nd lowest summer temperature on record there).
The highest 1-day rainfall was 313 mm recorded at Mount Cook on 27 December.
The highest wind gust was 172 km/hr, recorded at Mount Kaukau (Wellington) on 28 December.
Of the six main centres, Tauranga and Auckland were equal-warmest, Tauranga was the wettest but also the sunniest, Christchurch was the driest, and Dunedin was the coolest and cloudiest.