National Climate Summary – September 2011: Dry, sunny and cool start to spring

• Rainfall: Less than half of normal in Bay of Plenty, Gisborne, the West Coast, and Mackenzie country.  Generally dry elsewhere, except for Auckland, central Otago and coastal Southland. Driest September on record for Whakatane.
• Sunshine: Extremely sunny for North Island, and north and east of South Island. 
• Temperatures: Below average over North Island, also for Nelson, Marlborough, West Coast, Coastal Fiordland, south Canterbury. Near average elsewhere.
• Soil moisture: Already below normal for this time of year in north Canterbury, Mackenzie country and central Otago, as well as parts of the North Island.

 

September 2011 was characterised by higher pressures than usual over the Tasman Sea and lower pressures to the south and east of the country.  This pressure pattern produced more southwest winds than normal over New Zealand. 

It was a very dry month for most regions.  Less than half of normal September rainfall was recorded in Bay of Plenty, Gisborne, on the West Coast, and in the Mackenzie country.  It was the driest September on record for Whakatane.  It was generally very dry elsewhere, with below normal rainfall (between 50 and 79 percent of September normal). The only exceptions were coastal Southland (where rainfall totals between 120 and 149 percent of September normal were recorded), and Central Otago and Auckland (where near normal rainfall was experienced).  Soil moisture levels are already below normal for this time of year in north Canterbury, Mackenzie country and central Otago, as well as parts of the North Island. 

September sunshine totals were well above normal (more than 125 percent of normal) across much of the North Island, and the north and east of the South Island.  It was the sunniest September on record for Dargaville, New Plymouth, Tauranga, Dannevirke, Gisborne, Waipawa, Takaka, and Cheviot. For the remainder of the country, it was also a rather sunny September (with sunshine totals between 110 and 125 percent of normal).  The only exceptions were Fiordland and Southland, which experienced close to normal September sunshine hours.  

Mean temperatures well below average (between 1.2°C and 0.5°C below September average) across much of the North Island (with the exceptions of Coromandel, and parts of Auckland, Taranaki and Wanganui, where near average temperatures were recorded), as well as for most of Nelson and Marlborough, along the West Coast, coastal Fiordland, and south Canterbury.  In north Canterbury, Southland and Otago, temperatures were close to average (within 0.5°C of September average).   

The average temperature in September 2011 was 9.7°C (0.7°C below the 1971–2000 September average) using NIWA’s seven-station temperature series which begins in 1909.   

Further Highlights:

• The highest temperature was 22.3°C, observed at Hanmer Forest on 30 September.
• The lowest temperature recorded was -6.1°C at Pukaki Aerodrome on 14 September.
• The highest 1-day rainfall experienced was 98 mm recorded at Milford Sound on 10 September.
• The highest gust recorded was 126 km/hr at Castlepoint on 1 September.
• Of the six main centres in September 2011, Auckland was the warmest and wettest, Christchurch the coldest and driest, and Tauranga the sunniest.   

 

PRECIPITATION: less than half of normal in bay of plenty, gisborne, west coast and mackenzie country. generally very dry elsewhere, except for auckland, central otago and coastal southland.   

Less than half of normal September rainfall was recorded in Bay of Plenty, Gisborne, on the West Coast, and in the Mackenzie country.  It was the driest September on record for Whakatane.  It was generally very dry elsewhere, with below normal rainfall (between 50 and 79 percent of September normal).  The only exceptions were coastal Southland (where rainfall totals between 120 and 149 percent of September normal were recorded), and Central Otago and Auckland (where near normal rainfall was experienced).  Soil moisture levels are already below normal for this time of year in north Canterbury, Mackenzie country and central Otago, as well as parts of the North Island. 

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

 

 

SUNShine: extremely sunny over most of north island, as well as north and east of south island. 

September sunshine totals were well above normal (more than 125 percent of September normal) across much of the North Island, and the north and east of the South Island.  It was the sunniest September on record for Dargaville, New Plymouth, Tauranga, Dannevirke, Gisborne, Waipawa, Takaka, and Cheviot. For the remainder of the country, it was also a rather sunny September (with sunshine totals between 110 and 125 percent of normal).  The only exceptions were Fiordland and Southland, which experienced close to normal September sunshine hours (between 90 and 110 percent of September normal). No part of New Zealand experienced below normal sunshine hours in September 2011.

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

 

 

temperature: below average over much of north island, also for nelson, marlborough, the west coast, coastal fiordland and south canterbury. near average elsewhere. 

Mean temperatures well below average (between 1.2°C and 0.5°C below September average) across much of the North Island (with the exceptions of Coromandel, and parts of Auckland, Taranaki and Wanganui, where near average temperatures were recorded), as well as for most of Nelson and Marlborough, along the West Coast, coastal Fiordland, and south Canterbury.  In north Canterbury, Southland and Otago, temperatures were close to average (within 0.5°C of September average).   

The average temperature in September 2011 was 9.7°C (0.7°C below the 1971–2000 September average) using NIWA’s seven-station temperature series which begins in 1909 1.   

During the month of September, mornings were particularly cold (see minimum temperatures below), notably for eastern and central parts of the North Island.  Mean minimum temperatures were the lowest on record for September in Masterton, Takapau Plains, Martinborough, Wairoa and Waipawa (all North Island eastern sites), as well as for Motueka, Hanmer Forest, Orari and Timaru.  

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

 

 

Afternoon (maximum) temperatures were well down in September at a handful of sites, most notably at Greymouth, which experienced the coldest September mean maximum temperature there since records began in 1947.  

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

 

 
 

September CLIMATE IN THE SIX MAIN CENTRES  

For all of the six main centres, September 2011 was very dry, and extremely sunny.  Wellington, Tauranga and Dunedin experienced near average temperatures in September, but Auckland, Hamilton and Christchurch recorded below average temperatures.  Of the six main centres, Auckland was the warmest and wettest, Christchurch the coldest and driest, and Tauranga the sunniest.  

September 2011 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 

• Snow and ice

 

On 13 September, snow warnings were issued for SH87 from Outram to Middlemarch, and SH94 from Te Anau to Milford Sound.  

On 14 September, snow closed SH8 at the Lindis Pass from Tarras to Omarama, and SH73 from Arthurs Pass to Otira to towing vehicles, and chains were required by other vehicles.  

Snow affected SH94 from Te Anau to Milford Sound on 15 September, with all vehicles required to carry chains. Heavy snow closed Danseys Pass, with extreme care required on roads around Poolburn, Oturehua, St Bathans and Naseby. 

On 20 September, the Desert Road was closed by snow for a short time.  

• Rain and slips

 

The highest 1-day rainfall experienced in September 2011 was 98 mm recorded at Milford Sound on 10 September. There were no record high 1-day rainfalls during September. 

On 6 September, another slip came down on SH3 through the Manawatu Gorge, extending the closed period. 

• Temperatures

 

The highest temperature recorded in September 2011 was 22.3°C, observed at Hanmer Forest on 30 September. The lowest temperature observed was -6.1°C at Pukaki Aerodrome on 14 September.   

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

 

 

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

 

 

• Wind

 

The highest gust recorded during September 2011 was 126 km/hr observed at Castlepoint on the 1st. 

On 11 September, a tornado swept through the Auckland suburbs of Avondale and Te Atatu South, damaging homes, felling trees and downing power lines. The NIWA electronic climate station at Albany was also damaged. In the Hauraki Gulf, savage wind gusts caused problems for yachts in the Simrad 100 race, snapping masts and causing one yacht to run aground. Hawera recorded its highest September gust (98 km/hr) on the 11th, in records that began in 1986. 

On 13 September, wind warnings were issued for SH87 from Outram to Middlemarch, SH85 from Kyburn to Palmerston, SH8 from Lawrence to Milton, SH1 from Gore to Waihola, and SH90 from McNab to Raes Junction.  

Wind warnings were issued on 14 September for roads in Taranaki, Waikato, Auckland, Coromandel Peninsula, and western Bay of Plenty. A tornado in Pehiri Valley, inland from Gisborne, damaged property and uprooted trees.  

On 16 September, wind warnings were issued for SH1 between Gore and Waihola.  

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

 

 

• Lightning and hail

 

On 11 September, lightning hit property and power lines in the Auckland suburbs of Te Atatu South and Avondale, cutting power to some properties.  

A lightning storm swept across Wellington city on 13 September, with the accompanying marble-sized hail blanketing the ground, making some roads impassable. Several flights into Wellington were cancelled or delayed. About 900 homes in Eastbourne, Days Bay, and Evans Bay lost power for a few hours. In the Wairarapa, sleet and snow fell briefly. A separate storm brought hail to Gisborne on the same day.  

On 19 September, a very-localised, intense hailstorm was reported in Renwick, with small hail covering the ground, looking like snow. Lightning disrupted some telephone and television services.  

On 20 September, another hail storm struck Wellington. 

On 25 September, a hail storm coated some steep Dunedin streets, creating havoc for motorists.