July 2012: A month of two halves

National Climate Summary: July 2012 Issued: 6 August 2012

A month of two halves; cold & dry to start, then wet & warm

Overview
July started unusually cold and dry, due to winter time anticyclones or ridges prevailing over the country during the first half of the month, bringing clear skies, light winds and a recipe for frost. Frosts during the period 1 July to 5 July were particularly severe. In stark contrast, northwest winds produced unusual warmth in eastern areas mid-month. During the last two weeks of July, lows dominated over the north Tasman Sea, bringing unusually mild conditions, northeast winds and high rainfall to northern and eastern regions of the North Island, as well as Nelson/Marlborough.

For the month as a whole, higher than normal pressures were observed over New Zealand and to the southeast, with lower pressures than usual over the north Tasman Sea. This resulted in more northeast winds than usual over the North Island.
It was an extremely wet July (with more than 150 percent of July normal rainfall recorded) in parts of Northland, the Western Bay of Plenty, Waikato, Gisborne, southern Hawkes Bay, Wairarapa, Tasman, south Canterbury, and parts of Otago. Other regions which experienced above normal rainfall for July (between 120 and 149 percent of July normal) included Taranaki and Westland. In contrast, it was an unusually dry July for Southland, with rainfall totals less than 50 percent of July normal. It was the driest July on record for Invercargill and Tiwai Point. Rainfall was also below normal for much of north Canterbury, Fiordland, and between Wanganui and Waiouru (with totals between 50 and 80 percent of July normal). Elsewhere, near normal rainfall (between 80 and 120 percent of July normal) were generally observed. At the end of July, soils were much drier than normal in south Canterbury, but soil moisture levels were generally near normal elsewhere.

Because of the change mid-month from extremely cold and frosty conditions, to an unusually warm period, air temperatures for July as a whole were near average for many regions of the country (within 0.5°C of July normal). The exceptions were the south and west of the South Island, and along the northeast coastal margin of both Islands (where above average temperatures were observed, between 0.5°C and 1.2°C above the July average). Patches of below average temperatures (between 0.5°C and 1.2°C below the July average) were observed around Reefton. The nation-wide average temperature in July 2012 was 8.4°C (0.5°C above the 1971-2000 July average), using NIWA’s seven-station temperature series which begins in 1909.

It was an extremely sunny July for western and alpine regions of the South Island, with sunshine totals exceeding 125 percent of July normal. It was the sunniest July on record for Queenstown and Mt Cook. Above normal sunshine totals (between 110 and 124 percent of July normal) were observed in the central North Island, as well as Canterbury. In contrast, it was a rather cloudy July for Gisborne, Wellington, and Nelson (with between 75 and 90 percent of July normal sunshine experienced). Sunshine totals for July were near normal elsewhere (between 90 and 110 percent of July normal).

Further Highlights:
• The highest temperature was 22.6°C, observed at Rangiora on 15 July.
• The lowest temperature was -11.3°C, at Ranfurly on 2 July.
• The highest 1-day rainfall experienced was 336 mm at North Egmont on 15 July.
• The highest gust recorded was 132 km/hr at Cape Reinga on 29 July.
• Of the six main centres in July 2012, Tauranga was the warmest, wettest, and sunniest, Christchurch the coolest, Dunedin the driest, and Wellington the cloudiest.

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Rainfall: Extremely wet in Northland, Western Bay of Plenty, Waikato, Gisborne, southern Hawkes Bay, Wairarapa, Tasman, south Canterbury and parts of Otago. In contrast, it was unusually dry in Southland.

It was an extremely wet July (with more than 150 percent of July normal rainfall recorded) in parts of Northland, the Western Bay of Plenty, Waikato, Gisborne, southern Hawkes Bay, Wairarapa, Tasman, south Canterbury, and parts of Otago. Other regions which experienced above normal rainfall for July (between 120 and 149 percent of July normal) included Taranaki and Westland. In contrast, it was an unusually dry July for Southland, with rainfall totals less than 50 percent of July normal. It was the driest July on record for Invercargill and Tiwai Point. Rainfall was also below normal for much of north Canterbury, Fiordland, and between Wanganui and Waiouru (with totals between 50 and 80 percent of July normal). Elsewhere, near normal rainfall (between 80 and 120 percent of July normal) were generally observed.

At the end of July, soils were much drier than normal in south Canterbury, but soil moisture levels were generally near normal elsewhere.

Record or near-record July rainfall totals were recorded at:

Temperature: Near average temperatures experienced in many areas. Above average temperatures for the south and west of the South Island, as well as along the northeast coast of both islands.

Because of the change mid-month from extremely cold and frosty conditions, to an unusually warm period, temperatures for July as a whole were near average for many regions of the country (within 0.5°C of July normal). The exceptions were the south and west of the South Island, and along the northeast coastal margin of both Islands (where above average temperatures were observed, between 0.5°C and 1.2°C above the July average). Patches of below average temperatures (between 0.5°C and 1.2°C below the July average) were observed around Reefton. The nation-wide average temperature in July 2012 was 8.4°C (0.5°C above the 1971-2000 July average), using NIWA’s seven-station temperature series which begins in 1909 [Interim monthly value].

Record or near-record monthly-average maximum air temperatures for July were recorded at:

Record or near-record monthly-average minimum air temperatures for July were recorded at:

Sunshine: An extremely sunny July for the western and alpine South Island. Rather sunny across central North Island, too. Rather cloudy for Gisborne, Wellington, and Nelson.

It was an extremely sunny July for western and alpine regions of the South Island, with sunshine totals exceeding 125 percent of July normal. It was the sunniest July on record for Queenstown and Mt Cook. Above normal sunshine totals (between 110 and 124 percent of July normal) were observed in the central North Island, as well as Canterbury. In contrast, it was a rather cloudy July for Gisborne, Wellington, and Nelson (with between 75 and 90 percent of July normal sunshine experienced). Sunshine totals for July were near normal elsewhere (between 90 and 110 percent of July normal).

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

July climate in the six main centres

It was an extremely wet month for Tauranga, which recorded well over twice its usual July rainfall total. This ranked as the 4th-wettest July on record for Tauranga, with 328 mm of rainfall observed. There were several flooding events in the Western Bay of Plenty region during the month. It was also a wet month for Hamilton and Christchurch. In contrast, it was a relatively dry July for Dunedin.

Of the six main centres, Tauranga was the warmest, wettest, and sunniest; Christchurch was the coolest, Dunedin the driest, and Wellington the cloudiest.

July 2012 main centre climate statistics:

Highlights and extreme events

Rain and slips
The highest 1-day rainfall experienced in July was 336 mm, recorded at North Egmont on 15 July.
A severe thunderstorm crossed the Auckland region on 3 July, bringing torrential rain for a short time and causing surface flooding. The storm also caused power outages in parts of Browns Bay, Beachlands, Clevedon, Maraetai, Rotoroa Island, Whitford, Warkworth, and Waiheke Island. During the storm, a fur seal was found in a building in South Auckland 200 m from the harbour, and another seal was found inland in Devonport. Auckland Zoo was also flooded but no animals were harmed. In the Bay of Plenty, flooding closed SH2 north of Katikati. Both Waihi Beach and Katikati suffered flooding, with homes evacuated, and cars under water.
On 4 July, heavy overnight rain in the Gisborne area brought down the roof of a petrol station’s car wash and caused surface flooding on many roads in the district. Many sports grounds were closed.
On 6 July, heavy rain washed away a temporary road, closing SH56 at the Manawatu Gorge. Flooding also closed SH56 at the Manawatu River Bridge.
On 15 July, flooding and slips closed SH6 between Inangahua and Westport, and SH65 from Spring’s Junction to O’Sullivan’s Bridge. The Takaka-Collingwood Highway in Golden Bay was closed by flood debris on the road at the Waitapu Bridge. Many Nelson city roads were also closed by flooding.
On 16 July, SH73 was closed by a slip between Springfield and Arthurs Pass. Westport suffered surface flooding in the town, and was isolated by severe flooding and slips on SH67 from Westport to Greymouth, SH6 from Westport to Inangahua, SH67 from Westport to Karamea, and SH69 to Reefton. Minor flooding occurred in Murchison, with five homes inundated, and in Nelson where the Matai River overflowed. In Marlborough, the Wakamarina River overflowed its banks in several areas, and SH6 from Havelock to Wangamoa was closed by severe flooding. A fallen tree blocked the Picton end of Queen Charlotte Drive. In Wellington, the harbour ferry was cancelled because of the heavy rain and strong winds. In Upper Hutt, a woman was rescued from her vehicle attempting to cross the Akatarawa River, which had risen rapidly after the heavy rain, and a rock fall affected SH2 north of the Haywards Hill traffic lights. SH1 was closed by flooding between Taupo and Turangi, as was SH43 between Taumarunui and Whangamomona. SH3 was closed by a large slip north of the Awakino Hotel, and many minor roads in Taranaki were closed by smaller slips and surface flooding. At Coronet Peak, the ski area was closed after rain soaked the snowpack.
On 17 July, floodwaters isolated the King Country township of Ohura after the swollen Ohura River burst its banks. Several roads in the Ruapehu district were closed by flooding, slips or downed trees. The road to Rainbow Ski Field was closed after it was damaged by the heavy rain on 15 and 16 July. In New Plymouth, the Huatoki walkway was closed after heavy rain caused the path to slump. On 18 July, a large slip closed Gladstone Road, east of Levin, isolating 20 to 30 properties.
On 23 July, SH2 was closed by a slip in the Athenree Gorge and flooding in the Karanagahake Gorge, and reduced to one lane by surface flooding in the Papamoa area. SH26 between Paeroa and Te Aroha was closed by flooding. Katikati was also affected by flooding and both Katikati College and Katikati Primary School closed early. Waihi Beach was isolated after both roads heading into the town were closed. In the Coromandel, the Tapu-Coroglen Road was blocked by land slips. In Auckland, heavy rain brought down a tree in Titirangi, closing the road.
On 24 July, slips closed SH2 near Apata, and SH25 between Thames and Coromandel, and between Coromandel and Whitianga. In Gisborne, pupils were sent home from Kaiti School after flash floods entered classrooms and a toilet block. In the Waikato, flash floods inundated Cambridge homes, and a large slip left a 2 m high mound on Te Puroa Road, cutting off 24 properties, and isolating about 80 residents. In Hawkes Bay, the Clive River overflowed, damaging property, reserves and walkways.
On 25 July, one lane of SH35 was closed by a slip south of Hicks Bay. On 26 July, a slip closed SH25 on the Thames Coast at Ruamahunga Bay. In Wellington, a slip closed Raroa Crescent, one of the main routes into the city from the western suburbs. A slip also had to be cleared from SH2 at Horokiwi.
On 30 July, heavy rain caused a slip on SH29 near the summit on the Matamata side of the Kaimai Ranges, surface flooding on SH1 near the SH29 turnoff, SH26 between Paeroa and Te Aroha, and between Paeroa and Hikutaia, SH25 at the Thames Coast Road and further north at Manaia, and minor slips at Ruamahanga, Tapu and Kereta. In the Tauranga area, the heavy rain flooded roads, and the accompanying strong winds, brought down trees and power lines. In Dunedin, heavy rain caused surface flooding and property damage in the suburb of Helensburgh.
On 31 July, heavy rain caused surface flooding on SH8 between Fairlie and Lake Tekapo, SH79 between Fairlie and Geraldine, and SH83 between Duntroon and Kurow. Surface flooding closed many other roads in South Canterbury, including Dansey’s Pass, with SH1 between Pukeuri and the Waitaki Bridge requiring extreme care. In Christchurch, the Heathcote River burst its banks after two days of heavy rain, flooding the surrounding area. In Tauranga, heavy overnight rain caused the sewer system to overflow into the Waikareao Estuary. The Daisy Hardwick Walkway around the Waikareao Estuary was closed after a section of the seawall collapsed.
Record or near record July extreme 1-day rainfall totals were recorded at:

Temperatures

The highest temperature in July was 22.6°C, observed at Rangiora on 15 July. The lowest temperature was -11.3°C, recorded at Ranfurly on 2 July.

On 4 July, after several days of extremely cold weather, 10 parking meters in Gore lost their heads after water in the pipes froze, pushing the 20 kg cast iron tops off their stands.

A large number of records and near-records for highest minimum (morning) and maximum (afternoon) temperatures were observed in the second half of July, associated with the dominant northerly wind flows during that part of the month. July 15 was particularly warm in eastern areas.

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

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

Wind

On 3 July, strong winds lifted a roof in Hobson Street, Auckland, causing police to close the road until the roof had been secured.
On 29 July, a horse float was blown over on SH1 at Uretiti, south of Whangarei.
Lightning and hail

On 3 July, Waihi Beach was blanketed in hailstones.

Snow and ice

On 3 July, ice warnings were in place for SH6 and SH8 in Otago, SH94 to Milford Sound, and SH1 from Balclutha to Dunedin.

On 4 July, snow on SH73 at Porters Pass closed the road to towing vehicles. On 5 July a bonspiel call was put out for curlers to compete on the Idaburn Dam.

On 9 July, Frankton Marina on Lake Wakatipu was frozen, with the ice firm enough to allow curling. Jet boats could not be taken out because of ice in the Shotover River.

On 10 July, warnings were issued for SH8 which was affected by both ice and fog between Twizel and Lake Tekapo.

Cloud and fog

On 5 July, thick fog forced the cancellation of outgoing and incoming flights at Auckland Airport. Many other flights were delayed. Warnings were issued for SH1 in the Auckland region. On 6 July, fog again caused the cancellation or delay of flights at Auckland Airport. Fog also caused the cancellation of flights at Hamilton Airport and Christchurch Airport.

On 16 July, fog blanketed Nelson in the late afternoon, delaying flights into and out of Nelson Airport.

On 19 July, heavy fog blanketed parts of Auckland, causing the delay or cancellation of several domestic flights into and out of the airport.

On 24 July, heavy fog again caused the cancellation or delay of many domestic flights into and out of Auckland Airport. Flights were also cancelled at Whangarei, Kaikohe and Kerikeri airports.

On 25 July, fog again caused cancellations at Northland airports.

July 2012 rainfall, expressed as an anomaly from normal July conditions (% of July normal rainfall). Areas which received less than half of usual July rainfall are shown in yellow or orange colours (Southland and parts of Canterbury). Areas which were unusually wet (experiencing more than one and a half times the usual July rainfall) are shown in blue shades; namely Bay of Islands, Western Bay of Plenty, the Waikato, Gisborne, southern Hawkes Bay and the Tararua District, Tasman, Marlborough, south Canterbury, and northern and central Otago. Dots are climate station locations.

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