Autumn 2017

Wettest autumn on record for parts of the North Island

Rainfall 

Well above normal rainfall (>150% of autumn normal) was experienced across the majority of the North Island. Autumn rainfall was well above normal for parts of the northern and eastern South Island, including Nelson, Marlborough, and coastal Canterbury. A number of locations recorded their wettest or near-wettest autumn on record. The west and south of the South Island (south of Hokitika) experienced less rainfall than usual for autumn, with some locations recording well below rainfall (<50% of autumn normal).

Temperatures

Autumn 2017 temperatures were above average (+0.50°C to +1.20°C) for almost the entire North Island. There were pockets of well above average temperatures (> +1.20°C) in the Bay of Plenty and Auckland. The eastern side of the South Island mostly experienced near (-0.50°C to +0.50°C) or below average (-1.20°C to -0.51°C) temperatures. The western South Island observed above average temperatures.

Soil moisture

At the end of autumn 2017 soil moisture was well above normal along the east coast of the North Island south of Gisborne, around Whanganui, and in Marlborough, eastern Canterbury and Otago. Soils were drier than normal in mid-Canterbury, central Otago and southeast Southland. Soil moisture levels were near normal elsewhere.

Sunshine

Autumn sunshine was near normal (90-109% of autumn normal) for Northland to Waikato, the West Coast, inland Canterbury and parts of central Otago. Below normal sunshine (75-89% of autumn normal) was observed in central New Zealand (southern North Island and northern South Island).

Overview

For the autumn season as a whole, mean sea level pressures were above normal over and to the southwest of New Zealand, which resulted in more northeasterly winds than usual over the North Island and more easterly winds than usual over the South Island. The anomalous northerly flow over the North Island caused numerous moist, tropical airmasses to travel down to New Zealand, including two ex-tropical cyclones, which delivered significant amounts of rain to the top of the country during March and April. These rainfall events caused severe flooding and slips for parts of the North Island, particularly Auckland, Coromandel, and Bay of Plenty, as well as the top of the South Island. More details about these extreme events can be found in the Highlights and Extreme Events section below. Temperatures were generally warmer than usual for autumn across the North Island due to the northerly flows.

In contrast, the predominant easterly flow over the South Island caused wetter than normal conditions for the exposed regions of eastern Canterbury and Otago, but sheltering of western and southern parts encouraged drier than normal conditions to persist for the season in Southland, Central Otago and the West Coast. Temperatures were near average for most of the South Island, and slightly below average for parts of coastal Canterbury. In contrast, the sheltered West Coast experienced above average temperatures for autumn.

NIWA Climate Scientist Nava Fedaeff brings you highlights and statistics from Autumn 2017.

Further highlights

  • The highest temperature was 33.0°C, observed at Leeston on 17 March.

  • The lowest temperature was -6.9°C, observed at Middlemarch on 22 May.

  • The highest 1-day rainfall was 231.8 mm, recorded at North Egmont on 11 March. 

  • The highest wind gust was 167 km/hr, observed at Akitio on 19 May.

  • Of the six main centres in autumn 2017, Auckland was the warmest and sunniest, Tauranga was the wettest, Dunedin was the driest and Wellington was the least sunny, and Dunedin and Christchurch were both the coolest.

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Contact

Mr Chris Brandolino, Principal Scientist – Forecasting, NIWA National Climate Centre
Tel. 09 375 6335.