The tropical Pacific Ocean has returned to a neutral El Niño–Southern Oscillation (ENSO) state. Sea surface temperatures across the tropical Pacific have cooled to neutral levels over the past fortnight, supported by much cooler-than-average waters beneath the surface.
In the atmosphere, indicators such as the trade winds, cloudiness near the Date Line, and the Southern Oscillation Index have also returned to neutral levels.
Outlooks suggest little chance of returning to El Niño levels, in which case mid-May will mark the end of the 2015–16 El Niño. International climate models indicate the tropical Pacific Ocean will continue to cool, with six of eight models suggesting La Niña is likely to form during the austral winter (June–August).
However, individual model outlooks show a large spread between neutral and La Niña scenarios. Changes in the tropical Pacific Ocean and atmosphere, combined with current climate model outlooks, suggest the likelihood of La Niña forming later in 2016 is around 50%, meaning the Bureau’s ENSO Outlook remains at La Niña WATCH.
Typically during La Niña, winter-spring rainfall is above average over northern, central and eastern Australia.
Climate model outlooks for the Indian Ocean Dipole (IOD) suggest a negative IOD event is likely to develop during the austral winter. However, outlook accuracy for the IOD at this time of year is low. A negative IOD typically brings increased winter-spring rainfall to southern Australia.