A very wet winter for the eastern South Island, mild temperatures for most of the country

Rainfall

Rainfall was well above normal (> 149%) for parts of the eastern South Island from Christchurch to Oamaru. Rainfall was above normal (120-149%) in parts of eastern Otago, Nelson, Wellington and Northland. Below normal rainfall (50-79%) was observed in southern parts of Southland, Queenstown and Marlborough.

Temperature

Winter temperatures were well above average (> +1.20°C) for parts of Central Otago, and above average (+0.51°C to +1.20°C) in parts of Northland, Auckland, Bay of Plenty, Gisborne, Manawatu-Whanganui, Nelson, West Coast and the Southern Lakes. Temperatures were below average (-0.51°C to -1.20°C) in parts of Tasman and the Mackenzie Basin.

Soil moisture

At the end of winter 2017, soil moisture levels were above normal for the time of year for eastern parts of Otago and Marlborough. Soil moisture levels were below normal for isolated inland parts of Otago, and typically near normal for the remainder of the country.

Sunshine

Winter sunshine was above normal (110-125%) in parts of Southland and western Waikato. In contrast, below normal sunshine (75-89%) was observed in Christchurch and Wellington.

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Overview

Rainfall

Temperature

Sunshine

Overview

Winter 2017 got off to a relatively settled start, with record or near-record low rainfall totals for June in many North Island locations. In contrast, July was an active month due to the passage of several low pressure systems. Record-breaking rainfall was recorded in parts of Canterbury and Otago, leading to severe flooding and the declaration of a State of Emergency in those parts.

August was a warm month throughout the country, with abundant rainfall in western and central parts of the North and South Islands. For the winter season, overall, air pressures were higher than normal to the southeast of New Zealand and near normal across the country, with no significant airflow anomaly observed.

Further Highlights:

• The highest temperature was 23.2°C, observed at Kaikoura on 17 August.

• The lowest temperature was -14.6°C, observed at Tekapo on 29 July.

• The highest 1-day rainfall was 161 mm, recorded at Oamaru on 21 July.

• The highest wind gust was 170 km/hr, observed at Akitio (Hawke’s Bay) on 13 August.

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

• Of the available, regularly reporting sunshine observation sites, the sunniest four locations in 2017 so far (1 January – 31 August) were Whakatane (1646 hours), Blenheim (1608 hours), Richmond (1587 hours) and Napier (1552 hours).

Rainfall: A wet season for eastern parts of Canterbury and Otago

Rainfall was well above normal (> 149% of the winter normal) for parts of the eastern South Island from Christchurch to Oamaru. Oamaru observed its wettest winter since records began in 1941, with 285 mm of rain recorded during the season. Notably, Oamaru recorded 161 mm of rainfall in the 24 hours to 9 a.m. 22 July; this is 45 mm more than the total rainfall typically observed during the entire winter season. This heavy rainfall event resulted in widespread flooding, and the declaration of a State of Emergency in eastern parts of the South Island (see Highlights and extreme events section for more details). It was also a wet season in parts of eastern Otago, Nelson, Wellington and Northland where rainfall was above normal (120-149% of the winter normal). Much of the winter precipitation recorded in eastern parts of the South Island fell during southeasterly airflows. In the east of the South Island, much of the winter precipitation fell during relatively cold southeasterly airflows. These delivered considerable snowfalls to the Canterbury ski fields, particularly those situated farthest east.

In contrast, rainfall was below normal (50-79% of the winter normal) in southern parts of Southland, Queenstown and Marlborough. No locations observed record or near-record low winter rainfall totals, although Queenstown recorded just two-thirds (67%) of its normal winter rainfall. Remaining areas of the country typically observed near normal rainfall (80-119% of the winter normal).

At the end of winter 2017, soil moisture levels were above normal for the time of year for eastern parts of Otago and Marlborough. Soils in some eastern parts of Otago remained sodden after the flooding event in July, with pools of surface water still reported in the Taieri Plains (west of Dunedin). Soil moisture levels were typically near normal for the remainder of the country, except for isolated inland parts of Otago, where soils were drier than normal for the time of year.

Temperature: Near average or above average for most of the country

The nation-wide average temperature for winter 2017 was 8.9°C (0.5°C warmer than the 1981-2010 winter average, using NIWA’s seven-station temperature series which begins in 1909). This makes the winter of 2017 the 11th-warmest winter on record. Mean temperatures for New Zealand were near average during June and July. However, the country observed its third-warmest August on record, which brought spring-like temperatures to end the winter season for many parts of the country.

Winter temperatures were well above average (> +1.20°C of the winter average) for parts of Central Otago. Lauder observed its warmest winter since records began in 1924. In addition, Lauder’s mean minimum temperature for winter was 0.0°C, making 2017 the first time on record the winter mean minimum temperature has not been below freezing at that location. Winter temperatures were above average (+0.51°C to +1.20°C of the winter average) in parts of Northland, Auckland, Bay of Plenty, Gisborne, Manawatu-Whanganui, Nelson, West Coast and the Southern Lakes. Temperatures were typically near average (-0.50°C to +0.50°C of the winter average) for remaining parts of the country. The exception was parts of Tasman and the Mackenzie Basin, where winter temperatures were below average (-0.51°C to -1.20°C of the winter average).

Sunshine: Sunniest winter on record for Invercargill

Winter sunshine was above normal (110-125% of the winter normal) in parts of Southland, north Canterbury and western Waikato, with isolated locations observing well above normal sunshine (>125% of the winter normal). It was a particularly sunny season in Invercargill, which had its sunniest winter since records began in 1913. The city observed 129 hours more sunshine than normal for winter. In contrast, Christchurch and Wellington observed below normal sunshine (75-89% of the winter normal). Sunshine hours were typically near-normal (90-109% of the winter normal) for the remainder of the country.

Of the available, regularly reporting sunshine observation sites, the sunniest four locations in 2017 so far (1 January – 31 August) were Whakatane (1646 hours), Blenheim (1608 hours), Richmond (1587 hours) and Napier (1552 hours).

Winter climate in the six main centres

Temperatures were above average in Auckland and Tauranga, and near average for all other main centres during winter 2017. Christchurch received well above normal rainfall (151% of normal), and it was also a wetter than usual winter in Dunedin and Wellington. Sunshine was above normal in Hamilton, below normal in Christchurch and Wellington, and near normal for the remaining main centres. Of the six main centres in winter 2017, Auckland was the warmest, Dunedin was the driest, Tauranga was the sunniest, Christchurch was the coolest, and Wellington was the wettest and least sunny.

Highlights and extreme events

This section contains information pertaining to some of the more significant highlights and extreme events that occurred during winter 2017. Note that a more detailed list of significant weather events for winter 2017 can be found in the Highlights and extreme events section of NIWA’s monthly Climate Summaries. These monthly summaries are available online, and may be viewed at the following website: http://www.niwa.co.nz/climate/summaries/monthly

Rain and slips

On 22 June, heavy rain affected the Far North District. In Kaeo, two schools closed for the day because flooding affected bus services, and a preschool was also closed. Flooding affected SH1 near Horeke as the Waihou River breached its banks, and SH1 near Mangamuka was down to one lane due to flooding. SH10 east of Taipa was also affected by flooding. In Kaitaia, 54 mm of rain fell in just 10 hours, which was more rain than the total recorded during the first three weeks of June 2017 (52 mm).

On 21-22 July, heavy rain and high tides led to hundreds of homes evacuated and a State of Emergency declaration in Waitaki, Dunedin, Christchurch, Selwyn, Timaru and eventually the entire Otago region, as floodwaters inundated coastal parts of the eastern South Island. There were several slips including one large one on Otago Peninsula which cut off residents north of Harwood. Road closures were widespread across coastal Canterbury and Otago. Low temperatures overnight led to black ice on the roads and the NZTA advised caution to motorists. In Christchurch, the Heathcote River burst its banks leading to flooded streets in the suburb of Beckenham. Dozens of properties – largely in Henley (at least 35 properties) and the Taieri Plains remained evacuated on 25 July. At peak flow the Clutha River was flowing at 1800 cumecs, while the Taieri River peaked above 2000 cumecs. The Selwyn River was also flooded. Several rainfall records were set as a result of the storm. Oamaru had its wettest day on record (daily rainfall records began in 1950), with 161 mm of rain. Dunedin had its wettest July day on record (records began in 1918), with 89 mm of rain recorded.

Temperatures

On 12 and 13 July, a cold southerly outbreak led to many North Island and some eastern South Island locations observing near-record low maximum temperatures for winter.

Wind

On 13 July, strong winds struck the lower North Island. More than 9000 people were without power, and many flights at Wellington Airport were cancelled. Sustained 10-minute winds of 135.7 km/h were recorded at Baring Head between 8:40 a.m. and 8:50 a.m.; this is comparable to winds experienced over flat land during a category 3 tropical cyclone. During that time at Baring Head, the maximum wind gust recorded was 155.9 km/h. Climate stations at Brothers Island in Cook Strait and on Mt Kaukau (Wellington) recorded maximum wind gusts of 167 km/h on this day. In Seatoun (Wellington), wind gusts led to a large tree crashing through a house. There were reports of roofs lifted in other parts of Wellington.

The NIWA wave buoy near Baring Head consistently recorded a significant wave height (highest 1/3 of waves) greater than 6 metres between 5 a.m. and 8 a.m. on 13 July. Observed maximum wave heights were in the 10 metre range. The Interislander ferry was cancelled during this time.

Snow and ice

On 1 July, up to 30 vehicles were towed after SH8 between Twizel and Fairlie, and SH80 between Aoraki-Mt Cook and Ben Ohau, were closed due to snow. Snowfall also cut road access into Tekapo and Mt Cook, and contributed to two buses sliding off the road. Several day visitors to Tekapo were forced to stay for the night due to road closures.

Lightning and hail

On 6 July, Auckland flights were put on hold and some diverted as thunder, lightning and torrential rain passed through during the afternoon. The lightning warning was lifted at 6 p.m. Lightning also struck Sancta Maria College in Auckland, which triggered the fire alarm and “fried” the gym speakers. More than 700 lightning strikes were recorded across the Auckland region, with the Sky Tower taking four direct hits.

Cloud and fog

On 17 June, 60 regional flights were cancelled and 48 were delayed when fog descended on Auckland Airport. Four international flights were also affected by delays or diversions. A fatal car accident near Netherton (Waikato) was attributed to the foggy conditions.

ENDS

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