Seasonal Climate Outlook - October 2011 to December 2011
On 19 September, the Bureau of Meteorology released its latest three-month rainfall outlook for the period October to December 2011. A drier season appears more likely over Tasmania and southern Victoria. The main driver behind this outlook is the persistence of above average temperatures across the central to south-eastern Indian Ocean. The chances of receiving above median rainfall during the October to December period are between 30 and 40% over Tasmania, southern parts of Victoria and south-eastern SA. A positive Indian Ocean Dipole event is currently developing and this can cause drier conditions in south-eastern Australia during spring. The tropical Pacific is currently ENSO neutral, however steady cooling of the central Pacific Ocean since early winter has increased the chance of a La Niña returning during the last quarter of 2011. The next outlook report is due on 25 October.
The Bureau’s latest ENSO Wrap-Up, issued on 28 September, reports that the continued cooling of the central Pacific Ocean since early winter is consistent with a developing La Niña event for the last quarter of 2011. Atmospheric indicators support the leading climate models. However, if the trend continues, it appears that the event will be weaker than that of 2010/11. La Niña events raise the odds of above average rainfall across the north and east of the country, but don't guarantee it. For example, the latest observations from the Indian Ocean show a positive dipole event and, typically in spring, this can counteract La Niña conditions by increasing the odds of dry conditions over south-eastern and central Australia. In addition, sea surface temperatures around northern Australia are average to below average and are not as conducive to rainfall as they were at this time last year.