Climate Summary for April 2008

April 2008 Extremes: deluges in the north, but dry in the south

• Rainfall: Record high rainfall in Bay of Plenty/Taupo, double average in parts of Northland, Wellington, Nelson and Marlborough, below average over the southern half of South Island
• Soil moisture: Significant deficits remain in inland Otago and eastern Canterbury
• Temperature: Above average in the west of the North Island, below average in inland Canterbury and Otago
• Sunshine: Above average in the west and south of the South Island, below average in Auckland and Waikato

April was a month of extremes with floods in northern New Zealand, while it remained dry in the south. An active trough moved over the North Island and north of the South Island from 14-16 April producing flooding in many parts of the north of the North Island and Nelson. Rainfall rates as high as 40 mm in an hour occurred producing flash floods - one drowning seven people in Tongariro National Park - and lightning which killed a man in Northland. Another trough on 29-30 April produced further heavy rainfall from 29-30 April with flooding in Northland, Taranaki, Kapiti and Wellington. April rainfalls eliminated the severe and significant soil moisture deficits in most of the North Island. However significant soil moisture deficits (more than 100 mm) persisted in Canterbury, north and central Otago.

Rainfall was particularly high in the Bay of Plenty and Taupo where more than double (200 percent) the April totals occurred. Marlborough also had double the normal April rainfall. In contrast it was much drier than normal over the remainder of the South Island with half or less normal rainfall in the southwest.

It was another mild month with the national average temperature of 13.7 °C being 0.34°C above average. Mean temperatures were between 0.5 and 1°C above average in Coromandel, the Waikato, and from Taranaki to Manawatu, and parts at least 0.5°C below average in inland parts of Canterbury and Otago. It was generally sunny month over Wellington and much of the South Island, especially in the west and south.

There were more depressions (‘lows’) in the Tasman Sea to the northwest of the North Island than normal for April and more anticyclones than normal to the south and east of the South Island. This produced more frequent moist northeast winds onto the North Island, and drier easterlies on to the South Island compared with usual April airflows.

Further Highlights

• The highest temperature during April 2008 was 27.0ºC recorded at Culverden on the 15^th. The lowest air temperatures during the month was -5.1ºC recorded at Lauder in the South Island and -4.0 ºC recorded at The Chateau, Tongariro on the 20^th.
• The highest 1-day rainfall was 132 mm recorded at Takaka on the 14^th.
• The highest wind gust for the month was 137 km/h at South West Cape (Stewart Island) on the 21^st, in strong southwesterly conditions.
• Two tornadoes occurred, one on the 1^st near Westport, and the other on the 30^th 60 km north west of Napier.
• Of the five main centres, Auckland was the warmest, Wellington the wettest and sunniest, and Christchurch the driest.

Temperature

Mean temperatures were between 0.5 and 1°C above average in Coromandel, the Waikato, and from Taranaki to Manawatu, and at least 0.5°C below average in inland parts of Canterbury and Otago.

Rainfall

Rainfall was double (200 percent) of normal rainfall in Bay of Plenty and Taupo, the Hauraki Plains, Cape Reinga, the Bay of Islands, Wellington, Nelson and Marlborough. At least one and a half times (150 percent) of normal rainfall was recorded in other parts of Northland, the Central Plateau, North Taranaki, Kapiti Coast and Wairarapa.

Low rainfall occurred over the remainder of the South Island, with only a half (50 percent) of normal rainfall in the southwest of the South Island, Christchurch, and Alpine areas.

Sunshine

Above average sunshine hours (at least 110 percent of normal) occurred in Wellington and over much of the South Island. It was particularly sunny in the west and south of the South Island, where totals were at least 120 percent of normal. Sunshine totals were less than 90 percent of normal in Auckland and the Waikato.

Full report

• Full details of the April 2008 Climate Summary

For further information, please contact:

Dr Jim Salinger – Principal Scientist, Climate NIWA National Climate Centre – Auckland Phone +64 9 375 2053 [email protected]

Dr Jim Renwick – Science Leader NIWA National Climate Centre – Wellington Phone +64 4 386 0343 [email protected]

 

Acknowledgement of NIWA as the source is required.