National Climate Summary – May 2011: Warmest May on record

• Temperatures:  Warmest May since records began in 1909.  Temperatures more than 2°C above May average between Waikato and Christchurch, and in the Lakes District.     
• Rainfall:  A record wet May for Nelson.  Extremely wet for much of the North Island, as well as the Tasman District, Marlborough, Otago and south Canterbury. 
• Sunshine: Very cloudy for the South Island and southwest of the North Island. 

 It was the warmest May on record, using NIWA’s seven-station temperature series which began in 1909.  The average temperature for May was 12.9°C (2.2°C above the 1971–2000 May average).  The previous record-holder from this series was May 2007 (with an average temperature of 12.5°C, or 1.8°C above the 1971–2000 May average).  Monthly mean temperatures for May were at least 2°C above May average between the Waikato and Christchurch, as well as in the South Island Lakes District, with many records broken. For the remainder of the country, monthly mean temperatures were also well above average (between 1.2°C and 2°C above May average).  

New Zealand was affected by more northerly winds than usual during May, squeezed between low pressures over the Tasman Sea and anticyclones (‘highs’) parked east of the country.  These northerly winds contributed to the record-breaking May warmth, a record wet May for Nelson, and extremely high rainfall totals for many regions of the North Island (with at least 120 percent of normal May rainfall), as well as for Marlborough, the Tasman District, Otago and south Canterbury.  In contrast, southern Hawkes Bay, the Wairarapa, and Banks Peninsula experienced a very dry May (with rainfall about half of normal), and rainfall was below normal (between 50 and 79 percent of normal) in parts of Fiordland.    

Overall, May was a month of extremes.  May started with a heat wave on the West Coast of the South Island; on the 1st of the month, 26.7°C was observed at Hokitika and 25.0°C at Westport (both new May records). A tornado swept through Albany (Auckland) on the 3rd.  Flooding rains affected Otago on May 7/8, and Nelson and Takaka on May 25/26.   

Sunshine totals in May were below normal (between 75 and 90 percent of normal) for much of the South Island, and from Taranaki to Wellington.  It was the cloudiest May on record for Hokitika, Cromwell and Stratford.  In contrast, sunshine totals were above normal (between 110 and 125 percent of May normal) on the east coast of the North Island, and in parts of Northland. Elsewhere, totals were close to normal (between 90 and 110 percent of May normal). 

Further Highlights:

• The highest temperature recorded was 26.7°C at Hokitika on the 1st (a new May record there).
• The lowest temperature recorded was -4.8°C at Pukaki Aerodrome on the 29th.
• The highest 1-day rainfall of 289 mm was recorded at North Egmont on the 25th.
• The highest gust was 184 km/hr recorded at Southwest Cape on the 12th.
• Of the six main centres, Auckland was the wettest but also the warmest, Tauranga was the sunniest, and Christchurch was the driest. 

 

TEMPERATURES: warmest may on record.  temperatures more than 2°c above may average between waikato and christchurch.

 NIWA’s long-term temperature series from seven stations spread across New Zealand indicates this was the warmest May since the series began in 1909.  The average temperature in May, based on this series, was 12.9°C (2.2°C above the 1971–2000 May average) 1.  The previous record-holder was May 2007 (with an average temperature of 12.5°C, or 1.8°C above the 1971–2000 May average).   

Monthly mean temperatures for May were at least 2°C above May average between the Waikato and Christchurch, as well as in the South Island Lakes District, with many, many records broken (see Table below). For the remainder of the country, monthly mean temperatures were also well above average (between 1.2°C and 2°C above May average).  

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

 
Rainfall: record wet for nelson.  also very wet for much of the north island, as well as marlborough, tasman district, otago and south canterbury. 

It was a record wet May for Nelson and the northwest South Island (including Takaka, Lake Rotoiti, and Reefton), with rainfall between two-and-a-half times and three-and-a-half times May normal.  Extremely high rainfall totals were also observed for many regions of the North Island (with at least 120 percent of normal May rainfall), as well as for Marlborough, the Tasman District, Otago and south Canterbury.    

In contrast, southern Hawkes Bay, the Wairarapa, and Banks Peninsula experienced a very dry May (with rainfall about half of normal), and rainfall was below normal (between 50 and 79 percent of normal) in parts of Fiordland.    

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

SUNShine: very cloudy for the south island and southwest of north island.  

Sunshine totals in May were below normal (between 75 and 90 percent of normal) for much of the South Island, and from Taranaki to Wellington.  In fact, it was the cloudiest May on record for Hokitika, Cromwell and Stratford, with between only half and three quarters of usual May sunshine totals observed.  In contrast, sunshine totals were above normal (between 110 and 125 percent of May normal) on the east coast of the North Island, and in parts of Northland.  Elsewhere, totals were close to normal (between 90 and 110 percent of May normal). 

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

 MAY CLIMATE IN THE SIX MAIN CENTRES  

Of the six main centres in May 2011, Auckland was the wettest but also the warmest, Tauranga was the sunniest, and Christchurch was the driest.  For all of these six main centres, it was a record or near-record warm May, and for all except Christchurch, it was a very wet month.   
 

May 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 

Rain and slips 

The highest 1-day rainfall of 289 mm was recorded at North Egmont on the 25th. 

On 2 May, heavy rain caused flooding in Kaeo, and reduced SH10 to one lane north of Kaeo after a section of the road slumped by 60 cm. In Houhora Harbour the storm sank a launch at its mooring. Whangarei Harbour was closed for shellfish gathering after the heavy rain caused overflows from the city's sewerage system. In the Western Bay of Plenty, the heavy rain caused surface flooding in many areas, and slips on SH33 near Paengaroa, and on No3 Rd, Te Puke.  

On 4 May, SH30 was closed between Awakeri and Te Teko after storm damage caused subsidence of the road surface. A large slip wiped out the main pipeline carrying water from the two top springs to the public pools at Morere Hot Springs, and the Reserve was closed because of damaged tracks. 

Heavy rain caused flooding in Sumner on 7 May, and many homes with roofs damaged by the earthquake suffered more water damage. Record rainfall amounts were also observed on the 7th in Otago (see extreme rainfall table below).  On 8 May, heavy rain over a 12 hour period caused slips and surface flooding, and blocked drains in Alexandra and Dunedin. On the Otago Peninsula, multiple small slips closed Portobello Road between Dunedin and Macandrew Bay, as well as Highcliff Road. More slips and fallen trees blocked roads across the harbour at Carey’s Bay, and at least one house suffered significant damage. Parts of SH1 near Waimate were covered in surface water, with flooding at the intersection of SH1 and SH82, and many buildings in the town were flooded. Local roads were disrupted by slips and flooding, and at least five areas through the Waimate Gorge were washed out.  

On 11 May, a "boil-water" notice was issued for Patearoa, Ranfurly, Omakau, Naseby and Lake Roxburgh residents after the heavy rain on 8 May discoloured water supply sources. At Omokoroa, neat Tauranga, a huge slip came down leaving a house near the edge of a cliff.  

Heavy rain in Eastland on 13 May caused slips and flooding, closing SH2 at Waimana, and causing several slips on SH35, the coast road north of Opotiki. The wet weather was also blamed for the sudden appearance of large potholes along SH3 in Waiwhakaiho Valley just out of New Plymouth. 

On 15 May, heavy rain caused flooding in Wellington, with SH2 closed by a slip in Hutt Valley, and a slip near Johnsonville blocking train tracks and stopping services for several hours. 

Flooding closed some rural roads in Southland on 19 May. Heavy rain also flooded farmland north of Invercargill, and closed several roads, on May 20. 

On 25 May, heavy rain caused flooding in Ferntown, Golden Bay and around Sharlands Creek in Nelson.  On the 26th, further heavy rain flooded SH6 at Brightwater and between Havelock and Rai Valley, and SH60 at Takaka, with flood warnings issued for SH63 between Renwick and St Arnaud. Houses were evacuated at Hope and Brightwater. A house was evacuated in Nelson after a massive slip undermined its foundations. Slips closed the Takaka Hill Road, Matai Valley Road, and SH6 at Havelock. Further north, there was severe surface flooding in the northbound lanes of the Waikato Expressway at Rangiriri. Surface flooding up to 600 mm deep was reported in Tokoroa. In the Far North, SH1 was closed at the Rangiahua Bridge which was under water. SH1 was also closed by flooding between Pakaraka and Kaitaia. Surface flooding also covered SH10 at Kaeo. 

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

 

• Temperature

The highest temperature observed in May 2011 was 26.7°C observed at Hokitika on 1 May – a new May record there. The lowest temperature as recorded was -4.8°C at Pukaki Aerodrome on the 29th(not a record).   

Many locations set new all-time May records during the month. In particular, the first two weeks of the month were exceedingly warm. A record-breaking heat wave event occurred on the West Coast of the South Island and in Nelson, on May 1st, caused by foehn warming in strong easterly winds.   Auckland also broke a long-standing May temperature record on the 13th, hitting 24.6°C, as did Wanganui (with 22.7°C) on the 3rd.  

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

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

• Wind

 The highest gust recorded during May 2011 was 184 km/hr, recorded at Southwest Cape on the 12th. 

On 2 May, high winds are thought to have blown tree branches on to overhead power lines causing a power cut at Matua, Bay of Plenty. 

On 3 May, a tornado crossed the Auckland region, killing a man in Albany and injuring many others. Significant damage was done to property and vehicles, and many trees were blown over. One tree, with a 1 m thick trunk, was picked up and thrown into a nearby house, crushing the roof. Road were closed, causing serious traffic problems. 

On 11 May, storm damage resulted in a power outage lasting about an hour in western Auckland. At least two large trees were blown over, including one in the courtyard of St Matthew-in-the-City church in downtown Auckland, which toppled onto Wellesley Street, striking a man and causing minor injuries. Three ferry trips between Auckland and Waiheke Island were cancelled because of the high winds. In the Bay of Islands, yachts broke free of their moorings. 

On 12 May, wind warnings were issued early morning for SH1 between Kaikoura and Waipara, SH80 between Pukaki and Mt Cook, SH8 at both Burke’s Pass and Lindis Pass, and SH87 between Kyburn and Outram. During the day, serious damage was observed, with several people injured, 12,000 consumers losing power, roofs blown off buildings, cars damaged, and many roads closed between Mosgiel and Waikouaiti. One man was seriously injured when his car was badly damaged by a falling tree on SH1 near the Karitane turnoff. In Dunedin, people were blown over, and large trees were uprooted blocking Portobello Road, SH1 and SH88. Trucks were backed up on the northern motorway until fallen trees had been cleared. At Dunedin International Airport, six inbound and outbound flights were delayed, with one inbound flight cancelled, and two flights diverted, one to Invercargill and one to Queenstown. There was significant damage at Woodhaugh Gardens and in the Dunedin Botanic Gardens. The historic Matanaka Farm buildings at Waikouaiti were closed to clear fallen trees in the car park and along the tracks. In Hampden downed power lines arced, sparking together and setting the power pole's crossbeams alight. Fallen trees and power lines also closed SH97 in northern Southland. 

On 15 May, a mini-tornado in Atawhai, Nelson battered homes and swept away two trampolines, one of which flew 60 m over a house and caught on the top of a power pole. Power was cut for about an hour and a half. Mini-tornadoes also struck Wellington and the Kapiti Coast, felling 30 m trees. 

On 16 May, wind warning were issued for SH1 between Waihola and Gore, SH90 between Raes Junction and Gore, SH8 between Raes Junction and Milton, and SH87 between Outram and Kyeburn. 

On 17 May, high winds again caused damage, pulling off half the roof of an operations building at Napier Port, and a section of roof from a Hastings farm house, and in the harbour, a yacht broke from its mooring. In Wairarapa, gales cut power, brought down branches, and blew a four-tonne truck off SH2 near Mt Bruce. In the Nelson region, gales brought down trees and closed roads, including the Motueka Valley Highway where several hundred pine trees snapped off, and about 40 of the trees fell across the road trapping two trucks between them. Other local roads, including SH60 over Takaka Hill, were closed for short periods. At Ngatimoti, also in the Motueka Valley, five large macrocarpa trees were blown over, crushing two caravans and a truck. In Invercargill, trampolines were lifted and trees blown over, and in Waimate, a hay bale was blown off a truck.  

On 26 May, high winds in Wellington brought down a tree on to overhead lines on the Johnsonville railway line between Ngaio and Wadestown, halting trains. At Cooks Beach on the Coromandel Peninsula, two people were injured when a tree fell on their car in strong winds. In Waimate, the track to the White Horse monument was closed after high winds left more than four hectares of pine trees blown down along the mountain bike track and footpath. 

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

• Snow and ice

On 16 May, SH94 between Te Anau and Milford Sound was closed overnight by snow.  

On 18 May, road warnings for ice were issued for SH94, Lower Hollyford Valley to Milford Sound. 

On 20 May, snow was well below Stratford Mountain House on Mt Taranaki, with at least 8 cm in the upper car park. 

• Lightning and hail

 On 11 May, a Qantas passenger plane was struck by lightning soon after take-off from Auckland Airport. It re-landed safely.  

On 15 May, MetService reported nearly 6000 lightning strikes throughout New Zealand, with a garage set on fire in Paraparaumu, and radio transmitters hit, interrupting broadcasts in Wellington. Power was also cut to properties in the Riwaka Valley after lightning struck transformers on the Takaka Hill. 

• Fog

 On 3 May, thick fog obscured vision in the shipping lanes of Wellington Harbour. The fog also caused the cancellation of a flight from Blenheim. 

On 5 May, heavy fog delayed 15 domestic flights in and out of Auckland but did not affect international flights. 

On 24 May, fog caused cancellations and delays of both incoming and outgoing domestic flights from Auckland International Airport. Heavy fog in Christchurch also caused the diversion and cancellation of flights, including two international flights which were diverted to Wellington.