Seasonal climate outlook - January - March 2019

9 January 2019

Outlook summary

The atmospheric circulation around New Zealand is forecast to be characterised by pressures slightly higher than normal over and to the north of the country. For New Zealand, this pressure pattern will be accompanied by weak south-westerly quarter flow anomalies.
January through March 2019 mean air temperatures are most likely to be above average for the north of the North Island and about equally likely to be near or above average for the remaining regions of New Zealand.
During the January to March 2019 period, near normal rainfall is likely for most regions; however, the north of the North Island has about equal chances for below normal or near normal rainfall and the west of the South Island has about equal chances for above normal or near normal rainfall.
While oceanic patterns in the tropical Pacific currently reflect weak El Niño conditions, the atmosphere still hasn’t coupled with the ocean.
If this coupling does not eventuate, ocean anomalies in the Equatorial Pacific will have little relevance to New Zealand’s climate.
Sea surface temperatures are currently much warmer than average around New Zealand and warmer conditions are forecast to persist. This is likely to be a dominant driver of New Zealand’s climate.
For the current tropical cyclone season (November 2018 to April 2019), NIWA’s Southwest Pacific Tropical Cyclone Outlook indicates that the risk for New Zealand is near normal. On average, at least one ex-tropical cyclone passes within 550 km of New Zealand each year. Significant rainfall, damaging winds, and coastal damage can occur during these events.

January – March 2019 temperatures are forecast to be above average (50% chance) for the north of the North Island and above average or average (40 – 45 % chance) for all other regions of New Zealand.

January – March 2019 rainfall totals are forecast to be near normal (40% chance) or below normal (35% chance) for the north of the North Island and near normal (40% chance) or above normal (35% chance) for the west of the South Island. Near normal rainfall is most likely (45% chance) for all remaining regions of New Zealand.

January – March 2019 soil moisture levels and river flows are forecast to be in the near normal range (45 – 50% chance) in the South Island and for the west and east of the North Island. In the north of the North Island, near normal soil moisture levels are forecast (45% chance) and near normal or below normal flows are about equally likely (40 – 45% chance).

Regional predictions for the January – March 2019 season

Northland, Auckland, Waikato, Bay of Plenty

The table below shows the probabilities (or percent chances) for each of three categories: above average, near average, and below average. In the absence of any forecast guidance there would be an equal likelihood (33% chance) of the outcome being in any one of the three categories. Forecast information from local and global guidance models is used to indicate the deviation from equal chance expected for the coming three-month period, with the following outcomes the most likely (but not certain) for this region:

Temperatures are most likely to be above average (50% chance).
Rainfall totals are about equally likely to be near normal (40% chance) or below normal (35% chance).
Soil moisture levels are most likely to be near normal (45% chance).
River flows are about equally likely to be near normal (45% chance) or below normal (40% chance).