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Global setting – May 2015

An El Niño event is now under way in the tropical Pacific. In the second half of May, the Pacific trade winds weakened substantially and the Southern Oscillation Index (SOI) dropped below -1, indicating coupling had been achieved between the warmer sea surface temperatures and the overlying atmospheric circulation.

International guidance indicates that El Niño conditions are very likely (90% chance) to continue over the next three months period (June – August 2015). The likelihood of El Niño persisting or strengthening as we reach into spring is also very high (above 80%).

During June – August 2015, above normal pressure is forecast to the west of New Zealand, while below normal pressure is expected to the northeast of the country. This circulation pattern is likely to be accompanied with anomalous westerly to southwesterly wind flows. 

Sea Surface Temperatures

Sea surface temperatures for the coming three months are expected to be near average around the coasts of New Zealand. 

Differences from average global sea surface temperatures for 10 May to 6 June 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 mean values: May SOI -1.2; March to May average -0.8.
Differences from normal May surface temperatures in the seas around New Zealand.

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