Global setting: April 2016
El Niño conditions in the tropical Pacific weakened further during April 2016, with sea surface temperatures now typically only about +1oC warmer than normal.
Moreover, cooler than normal sub-surface waters have spread eastward from the western Pacific, and temperatures are more than 3oC below normal between 50 and 100m depth east of 160oW. These changes in sub-surface temperatures mean the tropical Pacific is poised to make a rapid transition into La Niña conditions.
International guidance indicates that neutral ENSO conditions are very likely (76% chance) over the next three month period (May – July 2016), as a whole. The likelihood of La Niña development increases into early spring, with a 52% chance over August – October 2016, and a further increase to 60% over November 2016 – January 2017. Forecast models indicate it is very unlikely (less than 10% chance) for a return of El Niño conditions during the rest of 2016. Because of the good chance of La Niña forming later in 2016, NIWA is on a La Niña “Watch”.
For May – July 2016, above normal pressure is forecast to the north and northeast of New Zealand. This circulation pattern is likely to be accompanied by anomalous north-westerly wind flow.
Sea Surface Temperatures
Sea surface temperatures are forecast to be above normal over the next three months, especially to the west of New Zealand.