National Climate Summary – May 2005

Wednesday June 1 2005

National Climate Summary – May 2005

Rainfall: Record high rainfall in the Bay of Plenty Temperature: Well above average throughout much of the North lsland, warm also in the north of the South Island Sunshine: Above average in the south of the South Island

While record rains lashed Bay of Plenty in May, the South Island received above average sunshine. The month was very warm over the North Island and northern South Island. There were two extremely high rainfall – flood producing events in the Bay of Plenty region over 3-4 and 17-18 May, both affecting Tauranga, and the latter devastating the coastal township of Matata.

Tauranga with 634 mm (695 percent of normal) had its wettest calendar month for any time of the year in more than a century, including its heaviest 1-day rainfall on record (347 mm on the 18th).

It was also very wet in Coromandel and parts of Hawke’s Bay. Soil moisture surpluses occurred in Bay of Plenty, the south and east of the North Island and in Marlborough. The national average temperature for May was 11.4°C, 0.7 °C above average.

May was very much warmer than usual in the North Island. However, temperatures were below average along the south Canterbury/Otago coast. Sunshine hours were well above average in inland south Canterbury and coastal areas of both Southland and Otago. However, they were below average in Waikato, King Country, along the Kapiti Coast, and in West Otago.

During May, depressions (‘lows’) were often centred northwest of the North Island. Most anticyclones (‘highs) occurred well away to the east or west of the country. More frequent northeasterlies occurred over the North Island and north of the South Island, contributing to the very wet conditions over much of the North Island.

Other Highlights: The highest temperature during May 2005 was 23.6°C recorded at Henderson (Auckland) on the 2nd. The lowest temperature for the month was -6.7°C, recorded at Ranfurly on the 18th.

Of the four main centres Dunedin was the driest, and Auckland the warmest. Rainfall was below average in Dunedin, but above average in the three other main centres. Temperatures were above average in Auckland, Wellington, and Christchurch, and below average in Dunedin. Sunshine hours were above average in Dunedin and near average in the other main centres.

Rainfall: Rainfall was at least 250 percent of normal in Bay of Plenty. It was also very wet in Coromandel and parts of Hawke’s Bay with totals of at least 200 percent of normal.

Rainfall was also above normal in Auckland, Waikato, Taranaki, Gisborne, Wellington, Marlborough, and parts of Northland and north Canterbury. Totals were less than 75 percent of normal in parts of Buller and Otago. Temperature: May was very much warmer than usual, with mean temperatures 1.0 to 1.5°C above average over much of the North Island, as well as much of Marlborough and Nelson.

The largest anomalies were in the central North Island, where mean temperatures were about 2.5°C above average. Temperatures were also above average in Buller, Westland, and north Canterbury. They were below average along the south Canterbury/Otago coast. Sunshine: Sunshine hours were well average in inland south Canterbury and coastal areas of both Southland and Otago. However, they were about 80 percent of average in Waikato, King Country and along the Kapiti Coast. It was also sunny in coastal Otago.

EXTREMELY HIGH RAINFALL IN BAY OF PLENTY

Rainfall was at least 250 percent of normal in Bay of Plenty (Tauranga recorded almost 700 percent of normal), due to the extreme high intensity rainfall events of 3-4 and 17-18 May. It was also very wet in Coromandel and parts of Hawke’s Bay with totals of at least 200 percent of normal. Rainfall was 125-200 percent of normal in Auckland, Waikato, Taranaki, Gisborne, Wellington, Kapiti, Marlborough, and parts of Northland and north Canterbury. In contrast, rainfall was less than 75 percent of normal in parts of Buller and Otago.

Near or record high May rainfall was recorded at:
Location May rainfall (mm) Percentage Of normal Year Records began Comments
Whitianga Airport 306 224 1988 3rd highest
Tauranga Airport 634 695 1898 Highest for any month
Te Puke 405 334 1973 Highest
Whakatane Airport 341 405 1975 Highest
Rotorua Airport 284 274 1964 3rd highest
Hamilton Airport 243 243 1935 Highest
Napier Airport 171 243 1951 Well above average

MUCH WARMER IN THE NORTH ISLAND AND THE NORTHERN SOUTH ISLAND

May was very much warmer than usual, with mean temperatures 1.0 to 1.5°C above average over much of the North Island, as well as much of Marlborough and Nelson. The largest anomalies were in the central North Island, where mean temperatures were about 2.5°C above average. Temperatures were at least 0.5°C above average in Buller, Westland, and north Canterbury. Mean temperatures were about 0.5°C below average along the south Canterbury/Otago coast, and near average elsewhere. Near or record high May mean air temperatures were recorded at:
Location Mean temperature Departure from average (°C) Records Began Comments
Kaitaia 15.9 +1.4 1985 Equal highest
Kerikeri EWS 15.4 +1.3 1982 Equal highest
Kaikohe 15.1 +1.8 1973 Highest
Dargaville 15.5 +1.7 1943 Highest
Whangarei Airport 15.7 +1.7 1968 Highest
Paeroa 14.2 +2.3 1947 Well above average
Tauranga Airport 14.1 +1.6 1913 Well above average
Te Puke 13.6 +1.7 1973 Highest
Whakatane Airport 13.1 +2.0 1975 2nd equal highest
Rotorua Airport 12.3 +1.9 1964 Highest
Taupo Airport 11.2 +2.4 1976 Highest
Motu 10.5 +1.8 1991 Equal highest
Mangere, Auckland 15.1 +1.4 1959 2nd equal highest
Auckland Airport 15.2 +1.6 1962 Highest
Pukekohe 14.4 +1.8 1971 2nd highest
Ruakura 13.4 +1.8 1907 3rd equal highest
Hamilton Airport 13.1 +2.2 1971 Equal highest
Mt Ruapehu, Chateau 7.5 +1.9 1930 3rd highest
East Taratahi 11.5 +1.6 1973 2nd highest
Gisborne Airport 13.5 +1.5 1905 Well above average
Napier Airport 13.1 +1.6 1974 Well above average
Paraparaumu Airport 12.8 +1.3 1953 3rd highest
Palmerston North Airport 12.5 +1.7 1962 2nd equal highest
Palmerston North EWS 12.9 +1.5 1928 3rd equal highest
Levin 12.9 +1.6 1896 3rd equal highest
Wallaceville 12.4 +1.9 1940 2nd equal highest
Ohakune 10.1 +2.5 1994 Highest
Wanganui, Spriggens Pk 13.5 +1.3 1937 3rd equal highest
Farewell Spit 13.4 +1.6 1971 Well above average

SUNNY IN THE SOUTH OF THE SOUTH OF THE SOUTH ISLAND

Sunshine hours were at least 120 percent of average in inland south Canterbury, and coastal areas of both Southland and Otago. However, they were about 80 percent of average in Waikato, King Country, and along the Kapiti Coast. Hours of bright sunshine were near average elsewhere.

Near record high May sunshine hours were recorded at:
Location May sunshine (hours) Percentage of normal Year Records began Comments
Lake Tekapo 185 141 1928 2nd highest
Invercargill Airport 111 138 1932 Well above average

MAY’S CLIMATE IN THE FOUR MAIN CENTRES

Of the four main centres Dunedin was the driest, and Auckland the warmest. Rainfall was below average in Dunedin, but above average in the three other main centres. Temperatures were above average in Auckland, Wellington, and Christchurch, and below average in Dunedin. Sunshine hours were above average in Dunedin and near average in the other main centres.
Location May Mean Temp. (°C) Dep. from normal (°C) May rainfall (mm) % of normal May Sunshine (hours) % of normal
Auckland 15.1a +1.4 Well above average 188b 183 Above average 135a 98 Near average
Wellington 12.4 +0.9 Above average 177 152 Above average 125 98 Near average
Christchurch 9.2c +0.3 Above average 86c 164 Above average 145 102 Near average
Dunedin 8.9 -0.3 Below average 48 67 Below average 126 126 Above average
a-Mangere b Mt Albert c Christchurch Airport

HIGHLIGHTS AND EXTREME EVENTS Temperature The highest temperature during May 2005 was 23.6°C recorded at Henderson (Auckland) on the 2nd. The lowest temperature for the month was -6.7°C, recorded at Ranfurly on the 18th. Widespread severe ground frost occurred in Nelson, Marlborough and Canterbury on the 9th, and in Otago and Southland on the 18th.

High rainfall, floods, and severe wind 1-2 May High rainfall (100 mm reported in 6 hours at Pohokura, and 80 mm in 3 hours at Motunui, Taranaki) resulting in slips and surface flooding closing SH 43, and the closure of a school. High winds, attributed to a tornado, also affected Taranaki, between Motunui and Urenui during the early morning on the 2nd, damaging an orchard, and destroying a farm shed.

3-4 May Torrential rainfall resulted in serious widespread flooding in Tauranga, especially in Otumoetai, Arataki, and Omanu. Many homes and businesses were flooded, with water a metre deep in areas, and emergency services were stretched to the limit. Rainfall totalling 144 mm was measured at Tauranga Airport in the 24 hours to 8am on the 4th. Heavy rainfall occurred between 3pm and 11pm on the 3rd, during which time there was 1-hour with rainfall totalling 67 mm. High rainfall also affected other sites in Bay of Plenty, as well as Hawke’s Bay, on the same day, many locations recording 75-100 mm.

17-18 May A phenomenal, unprecedented high-rainfall flood-producing event affected Bay of Plenty, particularly from Tauranga to Matata. Heavy rainfall occurred between 11pm on the night of the 17th and 8pm on the night of the 18th, during which time there were 6-hours with rainfall exceeding 30 mm per hour, and one hour with 58 mm. Tauranga Airport recorded a massive 346.8 mm of rainfall in 24-hours. This was well above any other daily rainfall total there in records which commenced in 1910, but comparable with those recorded for shorter durations on 17 April 1948, when 95, 146 and 212 mm was recorded in 1, 2 and 6 hours respectively. Rainfall totalling 94.5 mm in one hour was reported at Awakaponga, inland fro,m Matata. The New Zealand low lying land-station record was 109 mm in an hour recorded at Leigh (north of Auckland) on 30 May 2001.

High rainfall totals in Bay of Plenty for the mid-May rainfall event were:
Location Rainfall, mm 48 hours to 9am 19 May
Tauranga Airport 370
Te Puke 187
Whakatane Airport 127
Some of the effects of the storm were:

A state of emergency was declared on 18 May in Tauranga and Matata. There were hundreds of calls for emergency services. Police and army personnel assisted evacuations, while fire fighters pumped water from homes. Emergency personnel were also called in from outlying districts. About 450 people were evacuated for Tauranga, Papamoa, and Matata. In Tauranga, several city homes were destroyed by mudslides and floodwaters and rising waters threatened hundreds of others. The airport was closed by flooding.

Landslides threatened several homes and over a hundred residents were evacuated. More than 40 houses in Papamoa were evacuated. Many residents described the scene in Tauranga as a “disaster zone”. Several of the Tauranga houses had to be demolished. Flooding was extreme in Matata, where a stream became a torrent of water, mud, huge boulders, and debris.

Approximately 200 of the towns 500 people were evacuated. Houses were pushed off their foundations, nearly 100 being damaged, many motor vehicles were swept into the lagoon, some buried. Children were trapped in schools. One family became trapped in the roof of their home. Two houses and several caravans were swept out to sea. Railway lines were buckled, and about 20 motorists trapped. Parts of roads and two bridges near Matata on SH 2 were washed away. There was no drinking water supply.

It was stated that the town of Matata looked as through a tsunami had gone through it. At least one house was flooded in Edgecumbe, and there was surface flooding after 170mm of rainfall at Pongakawa and 150mm at Awakaponga on the 18th on the Rangitaiki Plains. The cost of the damage from this event has been estimated to be at least $40-50 million.

High winds The highest wind gust recorded during May 2005 was 152 km/h from the north, measured at Puysegur Point on the 1st.

Fog Wellington Airport was closed for several hours by fog and low cloud on the 19th and 20th. There have been 48 hours with fog there this year, the highest for any year in 45-years of measurement.

ENDS

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