Seasonal Climate Outlook: June - August 2016

02 June 2016

Ocean-atmosphere conditions in the tropical Pacific have now returned to near normal after a rapid demise of the El Niño event that peaked late 2015. Sea surface temperatures in the central Pacific are close to average, and slightly cooler than normal ocean temperatures have emerged along the equator in the eastern Pacific.

Atmospheric circulation along the equatorial Pacific has returned to near-normal, and the Southern Oscillation Index (SOI) has also returned to near neutral values. Cooler than normal sub-surface ocean waters have continued to intensify and spread eastward along the equatorial Pacific, suggesting the possibility of La Niña conditions developing later this year.

International guidance indicates that neutral ENSO (El Niño - Southern Oscillation) conditions are most likely (54% chance) over the next three month period (June – August 2016), as a whole, but a transition to La Niña is also possible over the same period (43% chance). The likelihood of La Niña conditions establishing in the Pacific increases later in the year, with a 58% chance in September-November 2016 and 61% chance in December 2016 – February 2017.

For June – August 2016, higher pressures than normal are forecast to the north and northeast of New Zealand, with lower pressures than normal expected to the south and the southeast of the country. Westerly to northwesterly wind flow anomalies are expected to affect the country.

Seasonal Climate Outlook Video

In the video below NIWA Forecaster Chris Brandolino describes what New Zealanders can expect, in broad terms, in the way of rainfall and temperature over the coming winter season:

Summary

June – August 2016 temperatures are very likely (65-80% chance) to be above average in all regions of the country. Nevertheless, frosts and cold snaps will occur from time to time in cooler locations. Sea surface temperatures are forecast to be above normal over the next three months, especially to the west of New Zealand.

June – August 2016 rainfall is likely to be above normal (50% chance) in the north and west of the North Island and the west of the South Island. Seasonal rainfall totals are equally likely to be near normal (40% chance) or above normal (40% chance) in the east of the North Island and the north and east of the South Island.

June – August 2016 soil moisture levels and river flows are most likely (45-50% chance) to be in the above normal range in the north and west of the North Island and the west of the South Island and most likely (40% chance) to be in the near normal range in the east of the North Island. In the North of the South Island, soil moisture levels and river flows are about equally likely to be in the near normal range (40% chance) or above normal range (35% chance). Soil moisture levels and river flows are both about equally likely to be in the near normal (40% chance) or below normal (35% chance) range in the east of the South Island.

Regional predictions for the June – August 2016 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 very likely to be above average (80% chance).
Rainfall totals are most likely to be above normal (50% chance).
Soil moisture levels and river flows are most likely (45-50% chance) to be in the above normal range.