National Climate Summary – August 2010: Cloudy, warm, and extremely wet

• Rainfall: Extremely wet for most North Island regions, as well as the north and east of the South Island. Double normal August rainfall for Kaitaia, Coromandel, Bay of Plenty and eastern Otago.
• Sunshine: Very cloudy for the North Island, as well as inland and eastern South Island.
• Temperatures: Above average for all regions, except eastern Otago.

August 2010 was characterised by lower pressures than normal over the Tasman Sea and New Zealand, resulting in a much wetter and cloudier August than normal.  Frequent northerly air streams affected the North Island during the month, with more easterly winds over the South Island.     

It was an extremely wet August across most of the country.  Rainfalls were well above normal (more than 150 percent of normal) for all of the North Island except Hawkes Bay, as well as in Nelson and Marlborough, and parts of Canterbury and Otago.  Double normal August rainfall was observed around Kaitaia, Coromandel and the Bay of Plenty, and eastern Otago.  It was the wettest August on record for parts of the Bay of Plenty, Wanganui and Turangi.  In contrast, Fiordland and Southland recorded below normal rainfall (between 50 and 80 percent of normal). For Hawkes Bay and the West Coast, rainfall was near normal (between 80 and 120 percent of normal).     

It was a very cloudy month over much of New Zealand.  August sunshine totals were below average (between 75 and 90 percent of normal) across the entire North Island, as well as for inland and eastern areas of the South Island.  Turangi, Stratford, Martinborough and Christchurch recorded well below average sunshine (between 50 and 75 percent of normal).  It was the cloudiest August on record for Turangi and Martinborough. Sunshine hour totals were closer to normal in the west and south of the South Island (ranging between 90 and 110 percent of normal).    

August 2010 mean temperatures were above average (between 0.5°C and 1.2°C above average) across all regions of New Zealand, except for eastern Otago, where temperatures were near average (within 0.5°C of average).  Small areas of well above average temperatures (more than 1.2°C above average) were observed in Northland, eastern Bay of Plenty, Nelson and Fiordland. The New Zealand national average temperature was 9.6°C (0.9°C above the 1971-2000 August average). 

Further Highlights:

• The highest temperature was 21.9°C, recorded at Motueka on the 15th (a new August record).
• The lowest temperature was -12.6°C, recorded at Lake Tekapo on the 10th (2nd-lowest August temperature on record there).
• The highest 1-day rainfall was 255 mm recorded at North Egmont on the 13th (not a record).
• The highest wind gust was 130 km/hr, recorded at Stephens Island on the 1st (not a record).
• Of the six main centres, Auckland was the warmest, Christchurch and Dunedin equally the coolest, Tauranga the wettest but also the sunniest, and Dunedin the driest.

 

Rainfall: extremely wet for most of north island, and north and east of south island. double normal august rainfall for kaitaia, coromandel, bay of plenty and eastern otago. 

It was an extremely wet August across most of the country.  Rainfalls were well above normal (more than 150 percent of normal) for all of the North Island except Hawkes Bay, as well as in Nelson and Marlborough, and parts of Canterbury and Otago.  Double normal August rainfall was observed around Kaitaia, Coromandel and the Bay of Plenty, and eastern Otago.  It was the wettest August on record for parts of the Bay of Plenty, Wanganui and Turangi.  In contrast, Fiordland and Southland recorded below normal rainfall (between 50 and 80 percent of normal). For Hawkes Bay and the West Coast, rainfall was near normal (between 80 and 120 percent of normal).     

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

 

 

SUNShine:  very cloudy across the north island, as well as for inland and eastern areas of the south island.  

August sunshine totals were below average (between 75 and 90 percent of normal) across the entire North Island, as well as for inland and eastern areas of the South Island.  Turangi, Stratford, Martinborough and Christchurch recorded well below average sunshine (between 50 and 75 percent of normal).  It was the cloudiest August on record for Turangi and Martinborough. Sunshine hour totals were closer to normal in the west and south of the South Island (ranging between 90 and 110 percent of normal).  

 

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

 

 

TEMPERATURES:  Above average temperatures for all regions, except eastern otago. 

August 2010 mean temperatures were above average (between 0.5°C and 1.2°C above average) across all regions of New Zealand, except for eastern Otago, where temperatures were near average (within 0.5°C of average).  Small areas of well above average temperatures (more than 1.2°C above average) were observed in Northland, eastern Bay of Plenty, in and around Nelson, on the West Coast and Fiordland. The New Zealand national average temperature was 9.6°C (0.9°C above the 1971-2000 August average)1.

 

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

 

 

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

 

 

AUGUST CLIMATE IN THE SIX MAIN CENTRES  

Of the six main centres, Auckland was the warmest, Christchurch and Dunedin equally the coolest, Tauranga the wettest but also the sunniest, and Dunedin the driest. 

August 2010 main centre climate statistics:  

 

a Mangere      b Tauranga Airport   c Hamilton Airport     d Kelburn     e Christchurch Airport    f Musselburgh  g Ruakura 
 

HIGHLIGHTS AND EXTREME EVENTS 

• Heavy rain and slips

 

On 1 August, heavy rain closed SH1 at Ngauranga Gorge, and caused flooding in the northern Wellington suburbs of Johnsonville and Newlands.  

On 4 August, a large landslip behind a house in the Wellington suburb of Karori made the house uninhabitable, forcing the residents to move out. Further north a storm lashed Northland, closing schools at Rawene and Opononi, while flooded roads cut off Omanaia School from either side. Surface flooding was also reported on SH1 near Houhora, in Whangarei, Kaeo, Waikare, and the Kai Iwi Lakes area. 

On 7 August, a large slip closed SH25 just south of Whangamata. In the South Island, SH1 was affected by surface flooding between Timaru and Waianakarua, and several minor roads in the area were closed by slips. 

On 8 August, a large slip closed northbound lanes of SH2 between Wellington and the Hutt Valley for about four hours. In Canterbury, the heavy rain caused slips and flooding, closing two roads overnight on Banks Peninsula. A slip at Greta Valley reduced SH1 to one lane. 

On 10 August, a large slip closed Ngaio Gorge Road, a major route from the northern suburbs of Wellington into the city.  

Heavy rain over the weekend of 14-15 August caused floods in the Bay of Plenty with a 10-metre breach in the Te Rahu Canal stop-bank off the Whakatane River. Several families were evacuated, and four schools and two pre-schools in Whakatane were closed. The Whakatane Boat Ramp was closed, phone lines were cut, and there was widespread surface flooding. Many roads around the region were closed, with Opotiki isolated. The Waioeka Gorge was closed by large slips, cutting off SH2 between Opotiki and Matawai, and surface flooding closed SH2 between Opotiki and Whakatane. A washout northeast of Opotiki closed SH35 to all but one lane of traffic, and the road between Taneatua and Kutarere was also closed by flooding.  

On 15 August, a slip blocked both lanes of SH1 between Picton and Blenheim. 

SH1, north of Oamaru, was affected by surface flooding on 30 August, after overnight rain. Grange Hill Road at Waihemo, North Otago, was closed by surface flooding, and other minor roads had caution notices in place. 

The highest 1-day rainfall recorded in August 2010 was 255 mm recorded at North Egmont on the 13th (not an August record at this site). 

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

 

 

• Temperature

 

The highest temperature recorded in August 2010 was 21.9 ºC recorded at Motueka on the 15th. This was the highest August afternoon temperature recorded there since records began in 1956. Maximum temperatures were extremely low on August 9th in Wellington and the Wairarapa. 

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

 

 

The lowest temperature recorded in August 2010 was -12.6 ºC recorded at Lake Tekapo on August 10th (this is the 2nd lowest August minimum air temperature recorded at this site since records began in 1925).  Numerous sites broke August minimum temperature records on the 2nd and 14th of August.  
 

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

 

 

• High winds

 

On 1 August, one car was blown into the path of another on the Rimutaka Hill Road section of SH2. The road was closed temporarily. 

A localised twister hit Hairini, just outside Tauranga, on 4 August, sending a shed roof flying across SH29. In Northland, high winds caused havoc.  A yacht broke its moorings and washed up on the beach at Waitangi, a trampoline was carried 30 m, bringing down power lines and cutting power, and a shed was flattened. 

On 12 August, the access to Mt Hutt ski field was closed because of high winds. About 1,000 people were forced to spend the night in the cafes.  

Crew from a Greymouth fishing vessel got into difficulties in gale force winds near Jackson Bay in the early hours of 13 August when their boat was caught by a wave that tipped it and stopped the main motor. All crew were transferred successfully to another vessel.  

The highest wind gust was 130 km/hr, recorded at Stephens Island on the 1st (not an August record at this site). 

Near-record high extreme wind gusts for August were recorded at:  

 

 
 

• Snow and ice

 

On 8 August, snow fell in inland Canterbury, with chains required for all vehicles driving over the high passes. Lindis Pass re-opened about mid-day after being closed overnight. The snow, and accompanying winds, disrupted several domestic and international flights at Queenstown Airport. In South Canterbury heavy snow brought down power lines in the Burkes Pass area, cutting power all day.  

On 9 August, SH1 between Waiouru and Rangipo was closed by snow and ice. Heavy snow in Dunedin’s hill suburbs created the usual difficulties for people trying to reach the city. 

• Lightning and hail

 

A fierce hailstorm on 29 August affected the Bay of Plenty, with particularly heavy falls in Tauranga. In Papamoa, lightning struck a home, blasting a hole through the roof, blowing off tiles, damaging the home’s wiring, and blowing a light switch out of its socket. Otumoetai College closed for the day as it had no power or hot water as a result of a blown power transformer. Other parts of the northern and western parts of the North Island experienced electrical storms, with thunder heard in Taranaki, Matamata, Auckland and Northland. 

• Fog

 

Heavy fog on 3 August caused delays to ferry services, and led to the cancellation of more than 50 domestic flights into and out of Auckland International Airport. The fog stretched as far as Hamilton, Rotorua and Taupo.  

Fog disrupted domestic flights in and out of Christchurch Airport on the morning of 23 August. It was fully operational by mid-morning.  
 

www.niwa.co.nz/ncc        Copyright NIWA 2010.  All rights reserved.