The Australian Bureau of Meteorology says Tropical Pacific Ocean temperatures have generally cooled over the past fortnight, easing towards neutral values (neither El Niño nor La Niña). Other ENSO indicators such as the Southern Oscillation Index (SOI) and tropical cloud patterns have remained at neutral levels. Given September is the time of year when El Niño events consolidate, this recent cooling is considered somewhat unusual and signals the risk of an El Niño event remains, says the bureau.
"Despite the shift towards neutral conditions, the tropical Pacific remains warmer than average," says the bureau. "When combined with the patterns of cloud and ocean temperatures in the Indian Ocean, conditions continue to favor below-average spring rainfall over much of Australia."
Climate models surveyed by the Bureau of Meteorology suggest sea surface temperatures in the tropical Pacific Ocean will maintain values around typical El Niño thresholds for the remainder of 2012 before returning to neutral values towards the end of 2012 or early 2013.
The Indian Ocean Dipole (IOD) is currently positive, with weekly values of the IOD index consistently above positive thresholds for the past two months. Outlooks from the Bureau's climate model indicate the IOD will most likely remain positive throughout the remainder of spring. A positive IOD is typically associated with decreased winter and spring rainfall over parts of southern, central and northern Australia.