More than 150% of normal rainfall was recorded for December in the North Island and northwest of the South Island. New rainfall records for the month were set in parts of the far north (Kerikeri 240%), Hawke’s Bay (Whakatu 467%), Wairarapa (East Taratahi 253%), central North Island (Turangi 246%), and Nelson (Lake Rotoiti 222%). A few localities in north Taranaki and eastern Bay of Plenty received over three times more rain than usual.
These high rainfalls contrasted with the drier than normal conditions in parts of Canterbury and Southland, where just 75% or less of average rainfall was recorded.
Air temperatures were about a degree higher than normal for the month, due particularly to unusually warm nights. Some locations in both the North and South Islands recorded overnight temperatures of 2 to 3 °C above average.
It was the least sunny December on record for some places, with 60 to 70% of normal hours of bright sunshine in many northern and western regions of both islands.
December was characterised by persistent low atmospheric pressures over the country, with moist northerly air flows much of the time – a conveyor belt of moisture from the sub-tropics that brought the heavy rain, frequent wet days, and warm, cloudy weather.
Percentage of average rainfall for December 2001 (recording sites shown with dots). Click to enlarge.
Difference from the average air temperature in degrees Celsius for December 2001. Click to enlarge.