Seasonal Outlook: October – December 2019

SEASONAL CLIMATE OUTLOOK

October – December 2019 Issued: 2 October 2019

NIWA Outlook: October – December 2019

Outlook Summary

• ENSO neutral conditions continued during September 2019, with sea surface temperatures (SSTs) near average for the time of year in the central equatorial Pacific.

• The Southern Oscillation Index (SOI) was -1.3 during September, an indication that the atmosphere was still responding to a residual warm pool of water in the west-central Pacific.

• Oceanic ENSO neutral will most likely continue (60% chance) over the next three months.

• During September, New Zealand’s coastal sea temperatures were cooler than average for all regions for the first time since 2017. This is expected to influence air temperatures during the October-December period.

• A strongly positive Indian Ocean Dipole event is expected to influence New Zealand’s climate over the next three months. More details in the Background section.

• 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.

• Temperatures are most likely to be near average for much of New Zealand, except the west and north of the South Island where there is about equal chances for near average or below average temperatures. Several sharp cold snaps are forecast during the first half of October.

• Rainfall is most likely to be near normal for much of New Zealand, except the east of the the South Island where near normal or above normal rainfall is about equally likely and the north of the North and South Island where near normal or below normal rainfall is about equally likely. An increase in westerly winds is possible later in October and November, which may lead to periods of unusually wet conditions, particularly in western areas.

October – December 2019 temperatures have about equal chances of being near average (45% chance) or below average (40% chance) for the west and north of the South Island. All other regions of New Zealand will most likely experience near average temperatures (50% chance).

October – December 2019 rainfall is about equally likely to be near normal (40% chance) or below normal (35% chance) for the north of the North and South Island and about equally likely to be near normal (40% chance) or above normal (35% chance) in the east of the South Island. Near normal rainfall is most likely for all other regions of New Zealand (45% chance).

October – December 2019 soil moisture levels and river flows are most likely to be near normal (35-40%) or below normal (35-40% chance) for all regions of New Zealand except for the east of the North Island where near normal soil moisture levels and river flows are most likely.

Full climate outlook: sco_october_2019_final.pdf

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