|Southeastern Aust Seasonal Rainfall Outlook: probabilities for October to December 2009, issued 22nd September 2009|
Drier December quarter favoured in southern parts of SE Australia
For southeastern Australia, the outlook for rainfall over the December quarter (October to December) shows a moderate to strong shift in the odds favouring a drier than normal season across southern areas, including Tasmania.
The pattern of seasonal rainfall odds across southeastern Australia is a result of recent warm conditions in both the Pacific and Indian Oceans. The Pacific influence (El Niño) has had the stronger effect.
The chances of exceeding the median rainfall for October to December are between 25 and 40% over Tasmania, much of Victoria and southeast SA (see map). This means that for every ten years with ocean patterns like the current, about six or seven years are expected to be drier than average over these regions, while about three or four years are wetter.
Across NSW and the remaining parts of both Victoria and SA, the chances of exceeding the median rainfall for October to December are between 40 and 55%, meaning that above average falls are about as equally likely as below average falls in these regions.
New: An expanded set of seasonal rainfall outlook maps and tables, including the probabilities of seasonal rainfall exceeding given totals (e.g. 200 mm), is available on the "Water and the Land" (WATL) part of the Bureau's website.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During October to December, history shows this effect to be moderately consistent over the western half of NSW, the eastern half of SA, Victoria and central Tasmania. However, confidence is only weakly to very weakly consistent over the northeast quarter of NSW and the western half of SA (see background information).
An unusual El Niño event persists across the Pacific Basin, with most leading climate models forecasting the event to peak late in 2009. El Niño events are usually (but not always) associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia. The SOI is approximately +3 for the 30 days ending 19 September. 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 detailed forecast maps, including the probabilities of seasonal rainfall exceeding given totals, can be found here.
More information on this outlook is available Monday to Friday from 9.00am to 5.00pm local time 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 23nd October 2009