Issued 10 November 1999
Map of the likely fire danger for the late December 1999/early January 2000 period based on projected seasonal climate forecasts. This is a scenario of a plausible, but not all possible outcomes, based on seasonal climate trend projections. This map will be updated on 10 December 1999.
NIWA November 1999 Outlook
More anticyclones should lie to the south and east of New Zealand, with more easterlies and north easterlies over northern New Zealand, and weaker westerlies to the south of the country. Anticyclonic anomalies are expected to continue during November, but with the axis of these shifting south and east with strongest anomalies lying at 45° S. Guidance suggests more north easterlies at times over northern New Zealand. This is consistent with recent anticyclone tracks across central New Zealand, and more northerly airflow. Above average temperatures are expected to continue in all districts, especially in the west of both islands, and inland Canterbury and Otago.
The more frequent easterlies and north easterlies are expected to produce above average precipitation in Northland, parts of Coromandel, Bay of Plenty, Gisborne and northern Hawke’s Bay. Significant rainfall is likely to fall on relatively few rain days in these districts. Below average precipitation is likely in the west of the North Island from Taranaki to Manawatu, the south west of the South Island, Marlborough, Southland and Otago. In other regions of New Zealand near average precipitation is likely. Fewer days of strong westerly winds are anticipated, particularly over southern New Zealand.
Below average rainfall. Below average rainfall is expected in the west of the North Island from Wanganui to Horowhenua. Rainfall is most likely to be below average in South Canterbury, North Otago and inland Otago and Southland. Other areas of lower than normal rainfall include Taranaki, Wairarapa, Wellington, coastal Marlborough, other parts of Canterbury, Otago and Southland.
High temperatures. Warm north westerlies are expected to be less frequent than normal. Although a few north westerly days will occur producing high temperatures in the east of both islands, the frequency of these will be lower than usual. With more anticyclones affecting southern New Zealand producing lower wind speeds, higher temperature extremes are more likely in inland areas of Otago and Canterbury. Warm north easterlies at times will also produce higher temperatures in the Waikato, King Country, and in the west of the North Island from Wanganui to Horowhenua.
Low humidity. Foehn westerly and north westerly winds bring with them low humidity. This factor is expected to be less accentuated than usual in the east both islands. Instead the areas receiving settled and drier and warmer conditions because of the anticyclones are expected to have lower humidity. Lower humidity periods are expected in inland areas of Canterbury, Otago and Southland as well as in the south west of the North Island from Wanganui to Horowhenua.
High winds. Higher wind speeds from north westerlies will occur in the east, but less often than normal. Instead, the odd low from the north is likely to bring higher wind speeds over the northern half of the North Island and through the Manawatu Gorge into the Manawatu.
The fire danger is expected to cxontinue increasing in inland areas of Otago and parts of South Canterbury to become very high. High fire danger is likely to develop in other areas between eastern Marlborough and eastern Otago, and spread in the south of the North Island between Wanganui and the Horowhenua. In central and southern Hawke’s Bay and Wairarapa, high fire danger is also likely. At the end of November, a moderate or low fire danger is expected in other parts of the country.
NIWA November 1999 – January 2000 Outlook
Over the early summer period, New Zealand should experience the effects of a moderate La Niña. Local sea-surface temperatures are likely to remain above average. More anticyclones (‘highs’) are expected east of the country, with warm northeasterly flow anomalies over New Zealand. Above-average temperatures are expected in all districts. Below-average rainfalls are likely in areas of Waikato, the southwest North Island, inland south Canterbury, Otago and Southland. Above-average rainfalls are expected to be patchy both in space and in time, affecting parts of the north and east of the North Island, Nelson, Marlborough and coastal north Canterbury. Winds are expected to be lighter than average over much of the country, with the exception of enhanced easterlies over the region from Auckland northwards. The incidence of warm föhn northwesterlies should be decreased in eastern areas of both islands.
Late December 1999/early January 2000 Fire Weather Conditions
The assessments below are an indicative scenario of the relative intensity of the contributing factors on the basis of the expected climate trends over the November 1999 – January 2000 period. Climate prediction is an emerging science and has naturally high uncertainties. These assessments will be revised in early December as the evolution of La Niña development into summer becomes clearer.
Below average rainfall. Below average rainfall is expected in the southern half of the South Island south of a line from Christchurch to Haast for the 10 week period. A moderate La Niña is very likely to produce extremely dry conditions in South Canterbury, and Otago. Below average rainfall and dry conditions are also expected from in the west of the North Island from south Taranaki to the Horowhenua.
High temperatures. More anticyclones to the east to the east of New Zealand and warm north easterlies are the likely climate pattern for the latter part of December/early January period. These usually bring lighter winds and clear skies with very warm temperatures occurring in inland areas of south Canterbury, Otago and Southland. Higher temperatures are also likely in the Waikato and King Country, and from south Taranaki to the Horowhenua in the west of the North Island.
Low humidity. Lower humidity levels for the late December/early January period are anticipated for inland areas of south Canterbury, Otago and Southland. With more easterlies and north easterlies over the North Island low humidity periods would also occur in Taranaki, Wanganui and Manawatu during periods of dry easterly winds.
High winds. Higher wind speeds are mainly expected when stronger easterly and north easterly winds occur. The chances of this occurring are higher in the north of the North Island, particularly exposed parts of Northland and Auckland. With the increased risk of easterly storms over the north, stronger dry easterly winds in coastal parts of Taranaki, Wanganui and Manawatu are more likely.
A fire danger index in the extreme range is possible in the drier parts of Wanganui and Manawatu, and in the east of the South Island from Christchurch in coastal Canterbury to Balclutha, including inland South Canterbury and Central Otago. A very high fire danger is likely in much of the Wairarapa and in other areas of the south west of the North Island from Wanganui to the Horowhenua. A high fire danger index is expected in other parts of the southern North Island. In the east of the South Island from the Kaikoura coast to eastern Southland, a very high fire danger is likely. The fire danger is expected to be moderate or low in other parts of New Zealand.