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Global setting – August 2015

Strong El Niño conditions are present in the tropical Pacific Ocean. Sea surface temperature anomalies in the central and eastern Pacific intensified during August 2015 and are now close to +2oC.

The Southern Oscillation Index (SOI) is strongly negative (-2.0 for August 2015, value estimated on the 2nd of September) and westerly wind anomalies (weaker trade-winds) dominate the central and western equatorial Pacific, indicating a strong coupling between the ocean and the atmosphere.

International guidance indicates that El Niño is certain (100% chance) to continue over the next three months (September – November 2015) and extremely likely (above 90% chance) to persist into summer 2015/2016. The current state of the ocean-atmosphere in the Pacific and the international consensus forecast suggest that this event could then rank amongst the 4 strongest El Niño events recorded (along with 1972/73, 1982/83 and 1997/98).

During September – November 2015, above normal pressure is forecast over and to the south of Australia, while below normal pressure is expected to the east of New Zealand.  This circulation pattern is likely to be accompanied with anomalous southwesterly winds.

 

Sea Surface Temperatures

Sea surface temperatures are forecast to be normal or below normal in the Tasman west of New Zealand, while surface water temperatures are expected to be in the below normal range to the east of the country.

Differences from average global sea surface temperatures for 9 August to 5 September 2015. Map courtesy of NOAA Climate Diagnostics Centre (http://www.esrl.noaa.gov/psd/map/images/sst/sst.anom.month.gif)
Monthly values of the Southern Oscillation Index (SOI), a measure of changes in atmospheric pressures across the Pacific, and the 3-month mean (black line). SOI preliminary mean values: August SOI -1.9; June to August average -1.5.
Differences from normal August surface temperatures in the seas around New Zealand.

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