TWM

NIWA
Climate Summary for February 2004

Rainfall: Extremely wet, with devastating floods, in the centre, south and west of the North Island
Wind: Much windier than usual, especially over the North Island
Temperatures: Below average overall, especially in the South Island
Soil moisture: Significant deficits persist in central Marlborough, Canterbury, and Otago, but surpluses in some North Island areas
Sunshine: Extremely low in the south and west of the North Island

A total of 30 monthly historical rainfall records were swept aside in a number of New Zealand regions during the exceptionally wet February that produced widespread flooding and extensive infrastructure damage. Rainfall was very much above average in the south and west of the North Island from Waikato to Wellington, including Wairarapa. It was a month of climate extremes, with seven heavy rainfall and at least three damaging high wind events. The reason for the exceptional climate pattern was an unusually high number of depressions (“lows”) to the south of the South Island, which often intensified as they passed over New Zealand. There were very few of the typical late summer anticyclones (“highs”). This pattern produced the strongest westerlies in over 60 years of records for February over the North Island, and southwesterlies over the South Island.

More than 1000 mm was recorded in the Tararua Ranges for the month. This was due to a number of high rainfall-flood producing events, on the 1st, and especially between the 14th and 18th of February. The latter, produced the most disastrous floods in the Wanganui, Manawatu/Rangitikei region for many decades, as well as flooding in southern Hawkes’ Bay, Wairarapa, Lower Hutt, and Picton. Hundreds of people were left homeless, considerable areas of farmland were inundated by silt and floodwaters, many rivers breached their banks, sheep and cattle stock were drowned or swept away by floodwaters, many bridges were damaged, and numerous roads closed, along with power, gas and water supply outages to tens of thousands of people. The cost of damage resulting from the floods has well exceeded $100 million. Further flood-producing rainfall occurred in parts of Northland, Auckland, Coromandel, Waikato, Bay of Plenty, King Country, and Taranaki on the 28th.
Rainfall was also above average in most other regions of New Zealand. Many locations experienced 7 to 10 more wet days than average for the time of year, some more. Unusually, soil moisture surpluses exist in some North Island areas, and the west of the South Island. However, soil moisture deficits remain high in parts of central Marlborough, Canterbury, and Otago. Temperatures were below normal. Sunshine totals were well below normal throughout the south and west of the North Island.

Highlights
The highest February 2004 temperature was 31.0°C, recorded at Alexandra on the 2nd.
The lowest temperature for the month was –1.1°C, recorded at Manapouri on the 26th.
High rainfall events were frequent during the month, affecting Northland, Auckland, Bay of Plenty, Waikato, Coromandel, East Cape, southern Hawke’s Bay, Wairarapa, King Country, Tongariro/ Ruapehu, Taranaki, Wanganui, Manawatu, Wellington/Lower Hutt, the Marlborough Sounds, Westland, and Fiordland. Most northern and western regions experienced at least two high rainfall events during the month. The most significant of these produced widespread rainfall totalling 65–150 mm in the 24 hours to 9 am on the 16th in many population centres (with very much higher totals in the high-country catchments) throughout the southwest North Island, from Taranaki to Wellington, as well as in southern Hawke’s Bay, Wairarapa, and the Marlborough Sounds, with further high rainfall in Wanganui and Taranaki on the 18th. The same weather event also produced storm-force southerlies and high seas, which buffeted parts of the North Island, from the afternoon of the 15th into the morning of the 16th. Ferry sailings were cancelled and considerable delays occurred at Wellington airport and other airports due to high winds. There were power cuts and fallen trees in some areas.
Gales (from the northwest) affected the Kapiti–Wellington region on the 21st, and around Dunedin (from the southwest) on the 24th.
A depression from the Tasman Sea and the remnants of tropical cyclone Ivy produced rainfall, in excess of 100 mm in parts of Northland, Auckland, Coromandel, Waikato, Bay of Plenty, King Country, and Taranaki on the 28th with houses flooded in Turangi as the Tongariro River overflowed its banks. Storm force northeasterlies gusted to 120 km/h at Cape Reinga, with gales also affecting Auckland.
Of the four main centres, Dunedin was the driest. It was very wet in Auckland, Wellington and Christchurch. Temperatures were below average in all four centres. Sunshine hours were below normal in Auckland and Wellington, and near normal in Christchurch, and Dunedin.

Rainfall
Rainfall was 400–600 percent (four to six times) of average February totals in much of the south and west of the North Island from Waikato to Wellington, including Wairarapa, and 200–300 percent of average in most other North Island regions, as well as Buller, north Westland, Marlborough and Nelson. Totals were also above average over much of the South Island.
Temperature
Mean temperatures were as much as 2.5°C below normal in the Southern Lakes, Central Otago, and inland Canterbury, and below normal in most other regions. However, Hawke’s Bay temperatures were above average. The February national average temperature of 16.1°C was 1.1°C below normal.
Sunshine
Sunshine totals were extremely low throughout the south and west of the North Island, and below normal in most other regions. However, sunshine was near normal in Canterbury and coastal Otago.

Acknowledgement of NIWA as the source is required.
© Copyright 2004 by NIWA


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