|Northern 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 northern 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 three months 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 range from 40 to 45% in the southern NT, northern SA and far southwest Queensland, to 50 to 55% in northeast Queensland (see map). So in years with ocean patterns like the current, about five September-quarters out of ten are expected to be wetter than average in northern Australia and five out of ten are expected to be drier.
However, it should be noted that July to September is the heart of the dry season across northern Australia and heavy rain is uncommon during this period
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 most of Queensland, the NT, northern SA and the northern border area of NSW (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 and the Northern Territory at the following numbers:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 24th JULY 2007