Seasonal Climate Outlook

Seasonal climate outlook September–November 2020

OUTLOOK SUMMARY

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 north-easterly air flow anomalies. The probability for oceanic La Niña conditions is 57 percent. The majority of NIWA’s criteria for “La Niña Alert” have now been met, including increased trade winds in the equatorial Pacific, an atmospheric response that is La Niña-like, and an expectation for these conditions to continue. This is consistent with other international agencies. New Zealand’s coastal water temperatures are well above average for the time of year and are expected to have an upward influence on air temperatures through spring. Air temperatures are most likely to be above average in all regions of New Zealand. Cold snaps and frosts can be expected in typically colder locations early in the season. Rainfall is about equally likely to be near normal or above normal in the north of the North Island, most likely to be near normal in the east of the North Island, and about equally likely to be near normal or below normal in all other regions. North-easterly winds are expected to continue to leave northern areas, such as Northland, the Coromandel Peninsula, and the East Cape, exposed to sub-tropical rain storms while interior and western areas of the both islands remain sheltered from moisture, particularly in South Canterbury, Otago, the West Coast, and Southland. Soil moisture levels are most likely to be below normal in the west and east of the South Island with river flows in the east most likely to be below normal. Near normal soil moisture levels

Photo: Caswell Images.