|National Seasonal Rainfall Outlook: probabilities for November 2009 to January 2010, issued 23rd October 2009|
Mixed rainfall odds for Australia
The national outlook for rainfall shows a mixed chance of exceeding the median rainfall over the late spring to mid-summer period (November-January). Drier than normal conditions are favoured for southeast Queensland and much of NSW, whereas above average three-month totals are favoured in the central and western NT, and northeast WA.
The pattern of seasonal rainfall odds across Australia is a result of higher than average temperatures in both the Pacific and Indian Oceans. The contribution of the warm Pacific biases the climate towards below average rainfall across eastern Australia. The warm Indian Ocean promotes wetter than average conditions across the tropics and in western WA.
The chances of exceeding the median rainfall for November to January are between 25 and 40% over southeast Queensland and the eastern half of NSW (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.
Contrasting this, the chance of wetter than average conditions is between 60 and 65% for western and central parts of the NT and northeast WA.
Across the rest of the country, including Victoria, SA, much of WA and Queensland, the chances of exceeding the median rainfall for October to December are between 40 and 60%, 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 the November to January period, history shows this effect to be moderately consistent over much of Tasmania, NSW, Queensland and the NT, but generally weakly consistent elsewhere (see background information).
An El Niño event persists across the Pacific Basin, with most leading climate models suggesting tropical ocean temperatures will remain above El Niño thresholds until at least early 2010. 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 −8 for the 30 days ending 20 October. 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.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Karl Braganza on (03) 9669 4344, Elise Chandler on (03) 9669 4748.|
Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 24th November 2009