Climate Update 40 - October 2002

Backgrounder

2002 rainfall to date
Most of New Zealand has received near normal rainfall. Parts of Waikato, Bay of Plenty, south Wairarapa, and Marlborough have been drier than average. Parts of Manawatu, Westland, Southland, and Otago have been wetter than average.

Total rainfalls for 1 January to 30 September 2002.
Update on the SOI
The mean Southern Oscillation Index (SOI) for September was -0.9, with the three month average now at -1.2. The present moderate El Niño is expected to be weaker than the 1997-98 event.

New Zealand Climate
Warm in the east
Daytime maximum temperatures were between 2.0 and 3.0 °C above normal in many eastern areas from Hawke’s Bay to Otago. The mean maximum temperature at Napier was 19.7 °C, which is the highest recorded since records began in 1870. Christchurch Botanical Garden reached 18.1°C, and was the highest since 1864. Records for September were also set at Kaikoura, Timaru, and Dunedin.
Dry in the east and wet in the west
Rainfall from Marlborough to north Canterbury was below average for the third consecutive month.

The outlook for October to December 2002
El Niño conditions are expected to last through summer 2002-03, but it is likely to be a much weaker event than that of 1997-98. Stronger than normal westerly winds are predicted during late spring.
Over most of the country, temperatures are expected to be average to above average. However, above average temperatures are likely in the eastern North Island, and below average temperatures are possible in the western South Island.
Near normal rainfall is expected for the North Island, except for the east where falls are expected to be below normal.

Soil moisture on 30 September
Conditions in the North Island were near normal at the end of September, with most areas at field capacity. The area of soil moisture deficit in eastern and northern South Island regions has shrunk slightly, but Marlborough, Canterbury, and Otago are still drier than normal. Western and southern South Island regions are near normal.

Soil moisture deficit in the pasture root zone at the end of September (right) compared with the deficit at the same time last year (centre) and the long term end of September average (left).