Global setting: May 2016

20 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.

Sea Surface Temperatures

Sea surface temperatures are forecast to be above normal over the next three months, especially to the west of New Zealand.

Differences from average global sea surface temperatures for 15 May - 11 June 2016. 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 0.4; March to May average -0.9.
Differences from average May surface temperatures in the seas around New Zealand.