Pacific approaches La Niña. Positive Indian Ocean dipole develops.
Issued on Wednesday 14 September | Product Code IDCKGEWWOO
Steady cooling of the central Pacific Ocean since early winter has increased the chance of La Niña returning during the last quarter of 2011. Current ENSO indicators are approaching values typically associated with La Niña events.
However, ocean temperatures are yet to reach critical thresholds, while climate model guidance about their future trends is mixed. Some models predict only modest cooling resulting in a borderline-La Niña event, but others predict stronger cooling beyond La Niña thresholds during the southern spring. A minority predict little or no cooling. Taken as a whole, there is an expectation that the trend towards La Niña will continue.
If a La Niña does form, current indicators are that it will be weaker than the strong 2010-11 event. La Niña events raise the odds of above average rainfall across the north and east of the country, but don't guarantee it. The Bureau's National Climate Centre will monitor the situation closely and issue regular updates via this summary.
The latest observations from the Indian Ocean show the development of a positive dipole event, as predicted over the last few months by climate models, including the Bureau's POAMA. Typically peaking in spring, positive dipole modes increase the chance of below average rainfall over southeastern and central Australia.