Climate Summary – May 2007: Warmest May on record

NATIONAL CLIMATE CENTRE MONDAY 4 JUNE 2007

National Climate Summary – May 2007: Warmest May on record
Indian summer in many parts of New Zealand; flooding in Nelson and Taranaki

• Temperature: New Zealand’s warmest May in over 140 years of temperature measurements
• Rainfall: Record low rainfall in the north and east, well above normal in Nelson
• Soil moisture: Significant deficits in the east of the North Island, as well as Otago
• Sunshine: Above average in many regions, especially in the east

May 2007 produced a truly Indian Summer for much of New Zealand with record temperatures for the month and the driest May on record in the north and east. This was produced by warmer than normal seas to the west of New Zealand and anticyclones to the east producing warm north westerlies over the country. The national average temperature was 12.4 °C (1.7 °C above normal); a new record for May, making it the highest in reliable records dating back to the 1860s. Similarly, Australia recorded its warmest equal May on record being 2.0°C above normal. At the same time a mere tenth to quarter of the normal monthly rainfall occurred in parts of the north and east of the North Island and the Kaikoura coast. Rainfall recorded in the east of the North Island and eastern Otago was 10 mm or less. The very dry weather meant that significant soil moisture deficits (of at least 110 mm) occurred in many eastern regions from Gisborne to Wairarapa, as well as Central Otago, unusual for the time of year.

May 2007 topped previous New Zealand temperature records of 12.3 °C in May 1962 and 12.2 °C in May 1999. Mean temperatures were at least 1.5 °C or more above average throughout much of New Zealand, but temperature anomalies were highest (more than 2.5 °C above normal) throughout Marlborough, Canterbury, and Otago, due to very frequent northwesterly winds. The month was the warmest on record averaged over the country as a whole. One third (35) of NIWA’s (104) near real-time New Zealand temperature stations recorded their highest May mean temperature.

Low rainfall was also a feature for May, with record low May totals in many northern and eastern regions. Rainfall was well below normal in the northern half of the North Island, as well as Gisborne, Hawke’s Bay, Wairarapa, along the Kaikoura coast, and in East Otago. In contrast, rainfall totals were 200 percent (twice) of normal in Nelson due to high rainfall over 22/23 May.

May was sunnier than normal in many North Island and eastern South Island locations.

Depressions (‘lows’) were much more frequent than normal south of Australia, while anticyclones (‘highs’) were more frequent than normal well to the east of the North Island. This pattern produced more frequent northwesterlies than usual over much of New Zealand, the strongest and most frequent for May since 1990.

Other Highlights:

• Parts of Nelson and Taranaki were hit by heavy rainfall over 22/23 May, with localised severe flooding.
• The highest temperature during May 2007 was 24.8 °C recorded at Whangarei Airport on the 1st.
• The lowest air temperature during the month was -4.1 °C recorded at Motu on the 31st.
• A wind gust as high as 156 km/h was recorded from the west at Taiaroa Head on the 27th.

• Auckland was the warmest, Dunedin the driest, and Christchurch the sunniest, of the five main centres. Rainfall was below normal and temperatures well above normal in all five main centres. Sunshine hours were above normal in Auckland, Wellington, Christchurch, and Dunedin, and near normal in Hamilton.

Temperature: Mean temperatures were at least 1.5°C or more above average throughout much of New Zealand, and more than 2.5°C above average in parts of Marlborough, Nelson, Canterbury, and Otago.

Rainfall: Rainfall was 25 percent (a quarter) or less of normal in parts of Northland, Auckland, Waikato, Taupo, Gisborne, Hawke’s Bay, Wairarapa, along the Kaikoura coast, and in East Otago, and 50 percent (half) or less of normal in Coromandel, Bay of Plenty, Wanganui, Manawatu, Horowhenua, Kapiti, North Canterbury, and inland Southland, and also below normal in Thames, Taranaki, Wellington, and much of Southland. In contrast, rainfall totals were 200 percent (twice) of normal in Nelson, and also above normal in Fiordland and parts of Marlborough.

Sunshine: May sunshine hours and/or solar radiation were more than 110 percent of normal in many North Island and eastern South Island locations, and at least 120 percent of normal in Gisborne, South Taranaki, Marlborough, inland South Canterbury, coastal Otago, and Southland.

TEMPERATURE: WARMEST MAY ON RECORD IN MOST REGIONS

The national average temperature was 12.4 °C (1.7 °C above normal); a new record for May, making it the highest in reliable records dating back to the 1860s, and highest on record at many recording stations. Mean temperatures were at least 1.5 °C or more above average throughout much of New Zealand, and more than 2.5 °C above average throughout Marlborough, Canterbury, and Otago.

Near or record high May mean air temperatures were recorded at:

Location Mean air
temperature
(ºC) Departure
from
Normal Year
Records
began Comments
Kaikohe 14.8 +1.3 1973 2nd highest
Dargaville 15.6 +1.7 1943 Highest
Whangarei Airport 15.6 +1.4 1968 Equal 2nd highest
Auckland, Henderson 15.0 +1.7 1986 Highest
Auckland, Mangere 15.4 +1.6 1959 Equal highest
Auckland Airport 15.1 +1.4 1963 2nd highest
Pukekohe 14.6 +1.6 1971 Highest
Whitianga Airport 14.1 +1.3 1991 Equal 3rd highest
Te Puke 13.6 +1.6 1973 Equal highest
Port Taharoa 15.4 +1.6 1982 Highest
New Plymouth Airport 14.2 +1.9 1944 Highest
Lower Retaruke 11.4 +1.5 1967 2nd highest
Chateau, Mt Ruapehu 7.6 +2.1 1930 3rd highest
Castlepoint 14.4 +1.6 1972 Highest
East Taratahi 11.9 +1.9 1973 Highest
Martinborough EWS 12.4 +1.8 2001 Highest
Ngawi, Palliser 15.1 +2.2 1972 Highest
Hicks Bay 14.9 +1.2 1992 Equal highest
Napier Airport 13.2 +1.5 1974 2nd equal highest
Wairoa, North Clyde 13.6 +1.6 1993 Highest
Mahia AWS 14.4 +1.9 1992 Highest
Paraparaumu Airport 13.4 +2.0 1953 Highest
Palmerston North Airport 13.0 +2.1 1962 Highest
Levin 13.2 +2.0 1896 2nd highest
Wellington, Kelburn 12.9 +1.4 1928 3rd highest
Wellington Airport 14.2 +2.0 1962 Highest
Wallaceville 12.7 +2.2 1940 Highest
Stratford 12.0 +1.8 1961 Highest
Wanganui,Spriggens Park 13.5 +1.3 1937 Equal 3rd highest
Wanganui Airport 13.6 +1.3 1979 2nd highest
Farewell Spit 14.1 +2.0 1971 Highest
Hokitika Airport 11.4 +1.4 1964 Equal highest
Milford Sound 10.1 +1.8 1935 2nd highest
Puysegur Point 11.6 +1.5 1979 2nd highest
Motueka, Riwaka 11.6 +1.6 1956 2nd highest
Nelson Airport 12.3 +2.2 1943 Highest
Blenheim Research 13.1 +2.5 1937 Highest
Blenheim Airport 12.1 +2.0 1941 3rd highest
Hanmer Forest 9.9 +2.3 1906 2nd highest
Kaikoura 13.6 +2.6 1964 Highest
Arthurs Pass 7.9 +2.7 1978 Highest
Mt Cook Village 8.6 +2.4 1931 Equal highest
Winchmore 11.4 +2.8 1950 Highest
Darfield 12.2 +3.0 1939 Highest
Christchurch Airport 11.4 +2.5 1954 Highest
Christchurch Gardens 12.1 +2.6 1864 Highest
Lincoln, Broadfield 11.8 +2.6 1881 Highest
Le Bons Bay 12.8 +2.6 1984 Highest
Lake Tekapo 9.5 +3.5 1927 Highest
Timaru Airport 10.1 +2.0 1962 Highest
Tara Hills 9.0 +3.0 1950 Highest
Wanaka Airport 9.7 +2.6 1993 Highest
Dunedin Airport 9.9 +2.2 1963 2nd highest
Dunedin, Musselburgh 11.2 +1.9 1948 2nd highest
Manapouri, West Arm 8.8 +2.1 1998 2nd highest
Queenstown 10.3 +2.7 1872 2nd highest
Queenstown Airport 9.1 +2.5 1969 Highest
Lumsden 9.8 +2.5 1982 2nd highest
Clyde 9.5 +2.8 1983 Highest
Gore 10.0 +2.5 1988 2nd highest
Invercargill Airport 10.3 +2.3 1949 Highest
Tiwai Point 11.1 +2.2 1970 Highest
Nugget Point 10.5 +2.0 1971 2nd highest
Raoul Island 20.1 +1.1 1940 3rd highest

RAINFALL: BELOW NORMAL IN MANY REGIONS, WELL ABOVE NORMAL IN NELSON

Rainfall was 25 percent (a quarter) or less of normal in parts of Northland, Auckland, Waikato, Taupo, Gisborne, Hawke’s Bay, Wairarapa, along the Kaikoura coast, and in East Otago, and 50 percent (half) or less of normal in Coromandel, Bay of Plenty, Wanganui, Manawatu, Horowhenua, Kapiti, North Canterbury, and inland Southland, and 75 percent (three quarters) or less of normal in Thames, Taranaki, Wellington, and much of Southland.

In contrast, rainfall totals were 200 percent (twice) of normal in Nelson (due to high rainfall over 22/23 May), and at least 125 percent of normal in Fiordland and parts of Marlborough.

Near or record low May rainfall was recorded at:

Location May
Rainfall (mm) Percentage
of normal Year
Records began Comments
Cape Reinga 19 26 1920 Lowest
Kaitaia Obs. 29 24 1985 Lowest
Kerikeri EWS 13 10 1982 Lowest
Kerikeri Airport 14 11 1978 Lowest
Kaikohe 23 20 1987 Lowest
Dargaville 22 20 1943 Lowest
Whangarei Airport 29 28 1991 2nd lowest
Warkworth 15 13 1972 Lowest
Auckland, Henderson 28 26 1986 Lowest
Auckland, Owairaka 23 23 1949 Lowest
Whitianga Airport 37 30 1991 2nd lowest
Te Puke 38 33 1973 Lowest
Whakatane Airport 21 27 1991 2nd lowest
Taupo Airport 10 13 1976 Lowest
Auckland, Mangere 11 11 1959 Lowest
Auckland Airport 12 13 1962 Lowest
Pukekohe 31 26 1986 Lowest
Ruakura 22 22 1906 2nd lowest
East Taratahi 8 10 1973 Lowest
Martinborough EWS 4 6 2001 Lowest
Hicks Bay 11 8 1992 Lowest
Gisborne Airport 7 8 1905 Lowest
Napier Airport 4 7 1951 Lowest
Wairoa, North Clyde 8 6 1992 Lowest
Mahia AWS 10 7 1991 Lowest
Paraparaumu Airport 33 33 1945 2nd lowest
Kaikoura 4 6 1949 Lowest
Rangiora EWS 11 21 1999 Lowest
Le Bons Bay 25 25 1984 Lowest
Ranfurly EWS 8 25 2001 Lowest
Middlemarch EWS 7 19 2001 Lowest
Dunedin Airport 9 15 1963 Lowest
Dunedin, Musselburgh 8 12 1918 2nd lowest
Nugget Point 20 19 1930 Lowest
Raoul Island 28 21 1938 Lowest

High May rainfall was recorded at:

Location May
Rainfall (mm) Percentage
of normal Year
Records began Comments
Nelson Airport AWS 153 199 1941 Well above normal

SUNSHINE: ABOVE AVERAGE IN MANY REGIONS, ESPECIALLY IN THE EAST

May sunshine hours and/or solar radiation were more than 110 percent of normal in many North Island and eastern South Island locations, and at least 120 percent of normal in Gisborne, South Taranaki, Marlborough, inland South Canterbury, coastal Otago, and Southland.

High May sunshine hours were recorded at:

Location May
Sunshine (hrs) Percentage
of normal Year
Records began Comments
Gisborne Airport 187 127 1905 Well above normal
Stratford 152 122 1963 3rd highest
Lake Tekapo 179 137 1928 Well above normal
Dunedin, Musselburgh 127 127 1948 Well above normal
Invercargill 122 152 1932 Well above normal

MAY’S CLIMATE IN THE FIVE MAIN CENTRES

Auckland was the warmest, Dunedin the driest, and Christchurch the sunniest, of the five main centres. Rainfall was below normal and temperatures well above normal in all five main centres. Sunshine hours were above normal in Auckland, Wellington, Christchurch, and Dunedin, and near normal in Hamilton.

May 2007 main centre climate statistics:

Location May.
Mean
Temp.
(°C) Dep.
from normal
(°C) May.
rainfall
(mm) % of
Normal May.
Sunshine
(hours) % of
Normal
Auckland 15.4 +1.6 Equal highest 23a 23 Lowest 149 108 Above normal
Hamilton 12.9 +1.2 Above normal 22 22 Well below
normal 123 94 Near normal
Wellington 12.9 +1.4 3rd highest 83 71 Below
normal 145 113 Above normal
Christchurch b 11.4 +2.5 Highest 18 35 Well below
normal 160b 113 Above normal
Dunedin 11.2
+1.9 2nd highest 8 12 2nd lowest 127 127 Well above normal
a Owairaka b Christchurch Airport

HIGHLIGHTS AND EXTREME EVENTS

• Temperature
The highest temperature during May 2007 was 24.8 °C recorded at Whangarei Airport on 1 May. It was also very warm on the same day in other parts of Northland, Auckland, Gisborne, and Hawke’s Bay, many locations recording maximum temperatures between 24.0 and 24.6 ˚C.

Record high May maximum temperatures were recorded on 1 May 2007 at:

Location Maximum
temperature ˚C Year
Records began
Kerikeri EWS 24.6 1982
Whangarei Airport 24.8 1968
Warkworth 22.9 1972
Auckland, North Shore ARC 24.5 1995
Whitianga Airport 22.8 1991
Hastings AWS 24.6 1982

The lowest air temperature during the month was -4.1 °C recorded at Motu on the 31st.

• Drought

Low rainfall meant that significant soil moisture deficits of 110 mm or more persisted in Hawke’s Bay, Wairarapa and eastern Otago throughout the month, a highly unusual situation for late autumn. Rainfall in the eastern North Island had been below average every month so far this year, and May’s conditions were severe enough to cause Hawke’s Bay farmers to sell stock due to insufficient feed for winter.

• High rainfall
There were several high rainfall events, with at least 75 mm in 24 hours. These were:

Date Region Location Rainfall (mm)* Other comments
2 May Waikato Matamata 71
6 May Fiordland Milford Sound 94
9-10 May Fiordland Milford Sound 209
20 May Fiordland
Aorangi Milford Sound
Mt Cook 133
127
22 May Nelson Nelson Airport 97 Flooding in some areas
31 May South Westland
Fiordland
Aorangi Franz Josef
Milford Sound
Mt Cook 95
131
117
* (9am-9am) rainfall

Parts of Nelson and Taranaki were hit by heavy rainfall over 22/23 May, with localised flooding. In Nelson, torrents of water washed down several Stoke streets, forcing the closure of a supermarket and three schools. Along the Taranaki coast, four houses were flooded and had to be evacuated, as the Oakura River overflowed its banks onto Hall Terrace. Even a car was swept downstream and into the sea. Water, in one house, was up to 2 m deep, with as much as 20 cm of mud and silt deposited on the floor. A man at the Timaru Stream managed to escape as raging water caught him on the swing bridge which was later torn and flung aside. Elsewhere, in New Plymouth, thigh-deep water flooded a motel at Burgess Park, where rainfall totalling 50 mm was estimated to have fallen in less than an hour. Official figures showed 63 mm in four hours at the Mangorei reservoir. New Plymouth airport recorded 35mm of rainfall between 7am and noon. Water was knee-deep in parts of the city, with a number of shops reporting damage.

• High winds
A wind gust as high as 156 km/h was recorded from the west at Taiaroa Head on the 27th.

ENDS

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