|Southeastern Aust Seasonal Rainfall Outlook: probabilities for July to September 2007, issued 26th June 2007|
50:50 chances for above average September-quarter rainfall
The outlook for total September-quarter rainfall (July to September) over southeastern Australia, shows no strong swings in the odds towards either above-normal or below-normal rainfall. The chances of accumulating at least average rain for the season are relatively close to 50%.
The pattern of seasonal rainfall odds across Australia is a result of recent higher than average temperatures (although with a cooling trend) in the tropical Pacific Ocean, and also in parts of the tropical and sub-tropical Indian Ocean. If, as computer models predict, the Pacific cools to such an extent that a La Niña forms during the next few months, subsequent issues of the seasonal rainfall outlook are likely to show increased chances of above average rainfall over eastern and northern Australia.
The chances of exceeding the median rainfall for the July to September period are between 40 and 45% in a band extending over most of SA, southwest Queensland, the far west of NSW, western and northern Victoria, and northern Tasmania (see map - note the Murray-Darling Basin is shown). Elsewhere the chances are between 45 and 55%. So in years with ocean patterns like the current, about five September-quarters out of ten are expected to be wetter than average in SE Australia and five out of ten are expected to be drier.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During July to September, history shows this effect to be moderately consistent across southern Queensland and large parts of NSW and SA. There are a few patches in Victoria and Tasmania where the effect is moderately consistent, but over most of those States the effect is only weakly consistent (see background information).
The Southern Oscillation Index (SOI) remained neutral in May and April with a value of −3 in both months. However, the SOI has risen over the past month to an approximate 30-day value as at 23rd June of +12. Computer models are still predicting the development of La Niña during winter. For routine updates and comprehensive discussion on any developments please see the ENSO Wrap-Up.
Click on the map above for a larger version of the map. Use the reload/refresh button to ensure the latest forecast map is displayed.
More information on this outlook is available Monday to Friday by contacting the Bureau's Climate Services sections in Queensland, NSW, SA, Victoria and Tasmania at the following numbers:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 24th JULY 2007