2005: Much Warmer

2005: Much Warmer, With More Anticyclones And Less Wind Than Normal Very Low Rainfall In The South Island Catastrophic Floods And Extremely High Rainfall In Bay Of Plenty;Destructive Tornadoes; An Unseasonably Late Snowstorm

New Zealand’s climate for 2005 was marked by too little rain in some places, and too much in others. Principal scientist Dr Jim Salinger of the NIWA National Climate Centre, says “Rainfall during the year was less than 75 percent of normal over much of the South Island whereas severe flooding in the Bay of Plenty in May caused widespread damage.

“The national average temperature of 13.1°C made 2005 the fourth warmest year nationally since reliable records commenced in the 1860s. Only 1971, 1998 and 1999 have been warmer with temperatures of 13.2, 13.3 and 13.3 °C respectively. Notable climate features in various parts of the country included heat-waves, low soil moisture, the Greymouth tornado, an unseasonable snowstorm, and damaging hailstorms.

The year was dominated by more anticyclones with less wind than average, although more easterlies at times occurred on to the north east of the North Island.”

“A weak El Niño prevailed in the equatorial Pacific during the first part of the year. More anticyclones in January commenced the trend of low rainfall and severe or significant soil moisture deficits in the northern half of the North Island and Canterbury; these conditions persisting into April.

Anticyclones and northeasterlies brought one of the warmest Februaries on record, with maximum temperatures of 30°C or more in many locations throughout New Zealand, and temperatures of 35°C or more in sheltered inland areas of the South Island during the first 10 days. March was wetter in the North Island, but more anticyclones in April kept conditions dry.

However, weather patterns changed abruptly in May. The Bay of Plenty floods of 3-4 May and 17-18 May were most disastrous, the earlier of the two causing widespread damage in parts of Tauranga, and the later being phenomenal, with unprecedented high-rainfall for the district and a state of emergency declared from Tauranga to Matata. Hundreds of people were evacuated. Homes were destroyed by mudslides and floodwaters and rising waters threatened hundreds of others. Flooding was extreme in Matata, where a stream became a torrent of water, mud, huge boulders, and debris”, says Dr Salinger.

Halfway through the year, more frequent anticyclones over the North Island and north westerlies over the South Island produced the sixth warmest winter on record, with extremely dry conditions in the east of the South Island. “Winter snowfall was much less frequent than normal. However, an early spring occurrence (on 19 September) to sea level in Canterbury was unusual for the month”, says Dr Salinger. This resulted in the closure of Christchurch Airport, along with schools and universities, with snow depths of 5-10 cm in the region. Power cuts also occurred. Hundreds of newborn lambs died in the cold.

More anticyclones over New Zealand continued into early spring, with milder conditions and below average spring rainfall, which resulted in significant soil moisture deficits developing much earlier than usual from Southland to Marlborough, and spreading to Nelson and the southwest of the North Island in November, and developing in Hawke’s Bay, Auckland, and parts of Northland in December. However southeasterlies in both October and November produced significant flooding in Gisborne. Patterns changed with warm northerlies producing the 3rd warmest December month.

“For the year there were at least 26 heavy rainfall events, half of which produced floods,” said Dr Salinger. There were also seven damaging hailstorms, and twelve damaging tornadoes (or events attributed to tornadoes) in 2005,” said Dr Salinger. The Greymouth tornado of 10 March was particularly destructive for a New Zealand occurrence, leaving 30 people homeless, and resulting in damage worth at least $10 million. Wellington Airport was closed for many more hours than usual in 2005. There were 52 hours with fog there, the highest for any year in 45-years of measurement.

NIWA analyses of month-by-month records and preliminary end of year data show:

• The year’s national average temperature of 13.1 °C (0.5 °C above the 1971-2000 normal), was the fourth warmest nationally since reliable records commenced in the 1860s.

• The highest annual mean temperature recorded for the year was 16.1 °C recorded at both Cape Reinga and Whangarei Airport.

• The highest recorded extreme air temperature for the year was 38.7 °C recorded at Alexandra on 5 February (the highest temperature there for any month, in records back to 1929). This is only one a few occasions when temperatures in New Zealand have exceeded 100 °F (37.8 °C).

• The highest temperatures during August 2005 were 25.1 °C recorded at Hanmer Forest on the 30th, and 25.4 °C recorded in Amberley on the 31st. These both exceeded the previous all-time New Zealand maximum temperature record for August.

• The lowest temperature for the year was -9.5 °C, recorded at Ophir (Central Otago) on 17 July.

• February was the 8th warmest on record.

• June was the coldest in a decade.

• July was the 3rd warmest on record.

• August was the 4th warmest on record.

• December was the 3rd warmest on record.

• The driest rainfall recording locations were Clyde in central Otago with 348 mm of rain for the year, followed by Lake Tekapo with 352 mm.

• Christchurch was easily the driest of the four main centres with 450 mm and Auckland the wettest with 1112 mm. Wellington received 975 mm and Dunedin 647 mm.

• Of the regularly reporting gauges, the Cropp River gauge in Westland, inland in the headwaters of the Hokitika River, recorded the highest rainfall with a 2005 annual total of 9290 mm.

• Nelson was the sunniest centre in 2005, recording 2571 hours, followed by Tauranga with 2495 hours, then Blenheim with 2466 hours. Auckland was easily the sunniest of the four main centres with 2254 sunshine hours, followed by Wellington (2211 hours) and Christchurch (2055 hours). Dunedin recorded 1807 hours.

• The highest recorded wind gust for the year was 174 km/h from the northwest, recorded at Southwest Cape (Stewart Island) on 3 April.

ENDS

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