National Climate Summary – Summer 2010/2011: Heat waves and deluges

NATIONAL CLIMATE CENTRE       Wednesday 2 March 2011.

• 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.  Tropical Cyclone Wilma moved rapidly across the northeastern North Island on January 28/29, causing widespread deluge rainfalls, severe flooding and slips in this part of the country.  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. 

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. 

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 in these regions.  Sumer temperatures were record or near record high across the northeast of the North Island, as well as in the north and east of the South Island (Nelson, Marlborough, Canterbury).    

Elsewhere in the South Island, seasonal temperatures were also above average (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)1. 

Record or near-record high summer mean maximum air temperatures were recorded at: 

 

 

Record or near-record high summer mean minimum daily air temperatures were recorded at: 

 

 
 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. 

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.  Tropical Cyclone Wilma moved rapidly across the northeastern North Island on January 28/29, causing widespread deluge rainfalls, severe flooding and slips in this part of the country.  And lastly, record-breaking rainfall occurred in Otago on 6 February. 

It was an extremely wet summer for many regions, 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 (see table below).  In contrast, Manawatu, Wellington, Wairarapa, Canterbury and Buller recorded closer to normal summer rainfall totals (between 80 and 120 percent of summer normal). 

Record or near-record high summer rainfall totals were recorded at: 

 

 

 

 

SUNShine: close to summer normal for most regions. 

Summer sunshine totals were close to normal in many regions of the country (between 90 and 110 percent of summer normal). The exceptions were Waikato, Coromandel, western Bay of Plenty, Gisborne, Wellington, Otago and the Lakes District, where below normal summer sunshine totals were experienced (between 75 and 90 percent of summer normal).  

Record or near-record summer sunshine hours were recorded at: 

 

 
 

 

SUMMER CLIMATE IN THE SIX MAIN CENTRES  

Summer 2010/2011 was very warm, and rather cloudy, at the six main centres.  Mean summer temperatures were the highest ever observed at Auckland Airport (since records began there in 1959), and were the 2nd-highest on record at Tauranga and Hamilton (where records began in 1913 and 1946, respectively).  Of the six main centres, for the summer of 2010/2011 as a whole, 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.   
 

Summer 2011 main centre climate statistics: 

 

a Auckland Aero except sunshine data from Mangere     b Tauranga Airport   c Hamilton Airport      d Kelburn  

  e Christchurch Airport     f Musselburgh    g Ruakura 

 

HIGHLIGHTS AND EXTREME EVENTS 

Rain and slips 

The highest 1-day rainfall for summer 2010/2011 was 313 mm recorded at Mount Cook on 27 December. 

On 18 December, heavy rain in the Eastern Bay of Plenty caused land slips, cut power, and blocked roads. Power was cut about 11 pm and restored mid-morning on 19 December. The forestry road, used as a detour for SH36, the main East Coast Rd, damaged by floods and landslides in winter and still under repair, was closed for a short time by surface flooding. The main road into the small town of Ruatoki was also blocked by slips. 

On 21 December, SH94 between Te Anau and Milford Sound was closed by a slip. SH6 was affected by flooding between Harihari and Haast. SH3 from Renwick to Nelson was closed by slips and flooding, and several roads in the Marlborough Sounds were also closed. On 22 December, the Department of Conservation issued a high alert for the Young Valley-Gillespie Pass circuit track, after heavy rain increased the risk the dam would burst and flood the valley below. 

Heavy rain hit Westland, the Southern Alps and parts of Otago on the 27th and much of the rest of the country on the 28th.  Several South Island roads were closed by surface flooding, including SH60 at Takaka, cutting off much of Golden Bay, SH6 at Renwick and at Canvastown (between Blenheim and Nelson), SH6 at the Lower Buller Gorge, SH63 between Arthurs Pass and Otira, SH73 between Otira and Kumara, SH69 from Inangahua to Reefton, SH65 from Murchison to Springs Junction, SH67 from Westport to Mokihinui, and SH7 from Hanmer Springs to Springs Junction. The James Road bridge in Bainham (on the Aorere River, near Collingwood) was washed away. A bridge in the Glen Roy Valley, near Murchison, was also washed out. The road to Ferntown, between Collingwood and the start of the Heaphy Track, was impassable. A slip across about 300 m of Readers Road near Havelock took out power poles and cut power. At Pelorus Bridge, campers waded through waist-deep water in the dark in an emergency evacuation at 4am, as the Pelorus River overflowed. Near Omarama in the Waitaki basin, severe rain forced campers to flee a free camping site near the Ahuriri River. 

Heavy rainfall was observed on January 18/19, associated with ex-tropical cyclones Vania and Zelia, which produced flooding on the West Coast and caused the Fox River to burst its banks, forcing some township residents to leave their property. SH6 was flooded north of Punakaiki, as well as between Greymouth and Runanga, and was closed by a mud slide near Reefton.  

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.  Many daily rainfall records were broken during this event between Taranaki and Wanganui.  In Auckland, flooding and a King Tide resulted in the Northern and Northwestern motorways being partially closed, and homes and businesses in the central city and coastal suburbs being flooded.  Several yachts were beached. A Taupo camping ground was evacuated, and the Desert Road was closed by a slip. On 24 January, the Waitomo Caves were closed to visitors because of rising river levels after heavy rain. Surface flooding covered the farm paddocks in the area.  

Tropical Cyclone Wilma moved rapidly towards the northeastern North Island during January 28th, causing widespread deluge rainfalls and severe flooding in northeastern regions of the North Island.  In Kerikeri, SH10 was closed by surface flooding after heavy rainfall associated with the cyclone. The waterfront at Paihia was flooded, and Paihia’s water treatment plant was damaged. Residents were asked to conserve water, while power was lost in other areas of the Far North, and in Whangarei. 

On 29 January, Wilma continued to affect the upper half of the North Island bringing torrential rain, although it was downgrading to an extra-tropical cyclone. SH25, the Thames coast road, was closed by a huge slip at Ruamahanga, with several other smaller slips also along the road. More than 500 visitors were stranded in Coromandel township, and Tapu camping ground also housed hundreds of campers. Flooding closed SH2 at Waimana Gorge, and also between Tauranga and Whakatane, with the access road to Tawharanui Beach near Matakana also cut off. Slips caused delays on SH25 near Whitianga, Kuaotunu and Whangamata, and on SH2 at Waioeka Gorge and Waiotahi Beach. Also in Whangamata, the heavy rain forced raw sewage to flow over properties and into the harbour after the treatment station at Awarua Point failed. On Waiheke Island, an 80 year-old house plunged down a cliff after a retaining wall was washed away. People from Kaeo to Kawakawa were evacuated from their homes because of rising floodwaters. In Whangarei, the Kamo bypass and parts of SH1 were closed, with detours in place. SH1 was also closed at Springs Flat, Kaeo, and Puketona Junction, with more than a kilometre of road under water at Kaeo. SH11 was closed by floodwaters between Kawakawa and Paihia. At Waihi Beach, motel units had to be evacuated because of flooding. Nine patients were evacuated from Waipuna Hospice at Te Puna until flood waters surrounding the hospital receded. All tracks on and around Mount Maunganui were closed by slips and mud slides. Sections of SH2 in Tauranga were affected by surface flooding, but remained open. 

On 30 January, farms in the low-lying Hikurangi swamp area of Northland remained submerged after flood waters breached stopbanks along the Mangakahia River. SH11 was closed between Opua and Paihia by flooding, and about 30 properties in Towai, Paroa Bay, Pokapu and Matawaia lost power. On 31 January, in Whakatane there was a potentially dangerous build-up of debris beneath the main bridge, and some roads were passable only by canoe. 

Extreme rainfalls were experienced in Otago and Southland on 6 February. During this event, heavy rain caused flooding in West and South Otago, with some roads impassable, and surface flooding over large areas of farmland, especially around Kelso and low-lying parts of Balclutha. In Timaru, the heavy rain brought down a tree which hit the 11kV power line, cutting power to homes southwest of the city.  On 8 February, the Land Transport Authority closed the twin bridges over the Waitaki River at Kurow, after high river flows damaged a bridge pier. 

Record or near record high extreme 1-day rainfall totals were recorded at:  

 

 

 

• Temperature

 

 

The highest temperature recorded in summer 2010/2011 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 second-lowest summer temperature recorded there since records began in 1949). 

During summer, an extremely cold spell occurred on December 8 – 9.  In particular, minimum temperatures in Otago and Southland on December 9th were record or near-record low.  In contrast, there were multiple heat waves during the summer.  Notably, several North Island sites broke summer maximum temperature records on January 17 – 18, while numerous stations in both islands experienced extreme warmth between 2 and 7 February.    

Record or near-record daily maximum air temperatures were recorded at:

 

 

 

Record or near-record summer daily minimum air temperatures were recorded at:

 

 

 

• Wind

 

 

The highest wind gust was 172 km/hr, recorded at Mount Kaukau (Wellington) on 28 December. 

On 21 December, high winds in central Christchurch downed a tree and crushed a parked vehicle. Spencer Beach Holiday Park in North Canterbury lost power after lines came down. Throughout Canterbury and North Otago, firefighters were called out to numerous vegetation fires started by the wind. In Timaru, gusts brought down power lines and power poles, cutting power to 3500 customers for about three hours. Trees were brought down across the Waitaki District, and wind-fanned fires closed SH82 near Waimate. High wind warnings were in force for high sided vehicles on SH77 from Darfield to Ashburton, SH75 from Halswell to Akaroa, SH7, the Lewis Pass, and SH73 from Springfield to Arthurs Pass. In Dunedin several flights were unable to land because of the strong northwesterly winds. Customers in the city and surrounding area lost power, roofs were lifted off homes, and firefighters tackled many fires triggered by the hot windy weather and arcing of downed power lines. In Marlborough, several large tree branches were brought down, blocking Kenepuru Road in the Marlborough Sounds. In the Rai Valley fierce winds blew a 10-m square shed from its foundation and threw it up to 40 m on to power lines in the Ronga Valley. The power lines were severed and arced cutting power to the area, and the shed was destroyed. In Wellington, wind blew over a tree which brought down trolley bus lines in Thorndon near the Botanic Gardens, blocking both lanes and causing traffic chaos, and in Mt Victoria, a toppled tree damaged a car. The Zephyrometer wind sculpture at the south end of Evans Bay was horizontal across the road at times in the northwesterly gales. One early-afternoon flight from Blenheim to Wellington was forced to turn back when strong winds at Wellington Airport prevented it from landing.   

On 22 December, high winds, heat, and downed power lines, set off a spate of fires from Invercargill to North Canterbury. At Leithfield Beach near Amberley, a large fire forced the evacuation of two households, and about 20 homes were evacuated near Rolleston until another fire was contained. The fires were extinguished by December 26th. 

On 24 December, a landboarder died when high winds flung him into a tree near Nelson. 

Several locations experienced very high winds on December 28th.  Gales caused havoc for emergency services around the lower North Island, bringing down trees and power lines. Police in Wellington said they received a call every two minutes between 7am and midday from people seeking information as the strong winds caused havoc in the city. A large pine tree fell over SH1 south of Mangaweka, between Taihape and Hunterville, and the road was down to one lane. The Rimutaka Hill Road was closed by high winds.   

On 15 January, a wind gust flipped one small plane on top of another at Queenstown Airport, causing extensive damage to both aircraft. Another plane had its tie-downs broken, but was not badly damaged.  

On 31 January, wind gusts of more than 100 km/hr lifted roofing iron, uprooted trees, demolished farm sheds, tore apart tunnel houses and felled power lines between Collingwood and Puramahoi. At Waitapu Gardens, a mini-tornado tore a 48 m plastic tunnel house off the pepper crop, flattened the corn crop, destroyed the beans, and ripped the tomato tunnel house in half. The back wall of Golden Bay Air's nearly-completed hangar at Puramahoi Aerodrome was blown out, and Farewell Spit Tours cancelled trips to the spit. 

On 2 February, record-breaking westerly winds occurred over the South Island and around central New Zealand. High winds and low cloud prevented the Canterbury Crusaders rugby team flying to Hokitika. The northwest winds also knocked down trees, damaging a 33 KV power line, cutting power to about 2500 homes near Leeston. In Fairlie, 15 power poles were snapped, cutting power to the town. SH80 between Lake Pukaki and Mt Cook, and SH8 between Fairlie and Twizel were closed to towing vehicles. Cautions were also in place for SH1 between Blenheim and Cheviot, and SH73 between Springfield and Arthurs Pass. In Te Anau, a mini-tornado ripped corrugated iron off classroom roofs at Fiordland College, flinging one sheet up to 150 m over trees and across a sports field. 

Near-record high extreme wind gusts for summer 2010/2011 were recorded at:  

 

 
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