Seasonal Climate Outlook

Our seasonal climate outlooks provide air temperature, rainfall, soil moisture and river flow predictions for the coming season.

Watch Chris Brandolino, NIWA Principal Scientist - Forecasting, explain how our seasonal climate outlooks can help your business succeed and how our seasonal climate outlooks can be interpreted.

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Issues

For April-June, air pressure is expected to be lower than normal to the northwest and higher than normal to the east of the country. Although air flows will be mixed, slightly more easterly quarter winds are favoured for the three month period as a whole.
During autumn, New Zealand’s climate patterns are expected to become more variable as the impact from a non-traditional central Pacific La Niña starts to ease.
Temperatures are most likely to be above average in the north of the North Island and about equally likely to be near average or above average in all other regions.
Sub-tropical air flows may fuel areas of localised, heavy rainfall that can cause flooding, similar to what was in experienced in parts of the country during late December and early January.
Consistent with moderate La Niña conditions, December 2020 – February 2021 air pressure is forecast to be higher than normal over and to the southeast of the South Island and lower than normal to the northwest of New Zealand. This is expected to be associated with northeasterly air flow anomalies.
November 2020 – January 2021 air pressure is forecast to be higher than normal over and to the southeast and lower than normal to the northwest of New Zealand. This is expected to be associated with northeasterly air flow anomalies, a signature of La Niña.
Air pressure is forecast to be higher than normal to the southeast and lower than normal to the north of New Zealand. This is expected to be associated with developing La Niña-like northeasterly air flow anomalies, although a westerly flow anomaly, which may be strong at times, is favoured to continue for much of October.
September – November 2020 air pressure is forecast to be higher than normal to the east and lower than normal to the northwest of New Zealand. This is expected to be associated with La Niña-like northeasterly air flow anomalies.
During periods of northeasterly winds, the threat for sub-tropical low pressure systems capable of producing heavy rainfall, similar to those experienced in late June and mid-July, is elevated, particularly in the north and east of the North Island.
Rainfall is about equally likely to be near normal or below normal in the west of the South Island, about equally likely to be near normal or above normal in the east of the North Island, and most likely to be near normal in all other regions.
Oceanic ENSO-neutral conditions will very likely persist over the next three months. The long-standing climate drivers that have contributed to dryness over much of NZ are expected to influence our weather for at least the first half of the winter season.
Sharp cold snaps are possible during the month of May as fronts move onto the country from the Tasman Sea and Southern Ocean.
Warmer than average ocean waters in the Coral Sea and west-central Pacific Ocean are expected to have some influence on New Zealand’s climate in the first half of the three month period.
Temperatures are mostly likely to be above average in the North Island and about equally likely to be above average or near average in the South Island.
Temperatures are expected to be near or above average for all regions of New Zealand except the north of the North Island where above average temperatures are most likely.
The weakening of the Southern Annular Mode and the Indian Ocean Dipole and the forecast for ENSO to remain neutral over the next three months indicate the absence of strong, persistent climate drivers for New Zealand.
Temperatures for the summer season are expected to be above average for New Zealand, apart from the west of the South Island where there are about equal chances for near average or above average temperatures.
For November to January, air pressure is forecast to be lower than normal to the southwest of New Zealand and higher than normal to the north. This is expected to be associated with a westerly quarter air flow anomaly.
For October to December, air pressure is forecast to be lower than normal in the New Zealand region, especially south of the country. This is expected to be associated with a westerly quarter air flow anomaly, particularly during November and December. Occasional easterly quarter winds are possible during October.
The central Pacific El Niño event that arrived in March 2019 has ended, giving way to ENSO neutral conditions, owing to cooling sea surface temperatures (SSTs) in the tropical Pacific and a neutral Southern Oscillation Index (SOI) during August.
Despite a sharp cold snap in early August, seasonal temperatures are forecast to be near average or above average for all regions of New Zealand, owing to warmer than average coastal and regional sea surface temperatures.
A weak, central Pacific El Niño continued during June as sea surface temperatures (SSTs) remained more than 0.7˚C above average (i.e. the El Niño threshold) for the fourth consecutive month.
Although El Niño is forecast to continue during the upcoming three-month period, it may weaken later in 2019. Winter temperatures are forecast to be above average in the east of the South Island and to be above average or near average in all remaining regions.
A weak, central Pacific El Niño continued during April, as patterns of enhanced rainfall persisted in the vicinity of the International Dateline. More westerly quarter winds than normal. Tasman Sea surface temperatures may influence several spells of unseasonable warmth through the season, particularly in eastern areas, contributed to by frequent westerly air flows.

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