|Southeastern Aust Seasonal Rainfall Outlook: probabilities for October to December 2007, issued 25th September 2007|
Odds favour drier December quarter in parts of far SE Australia
For southeastern Australia, the outlook for total December quarter rainfall (October to December), shows a moderate shift in the odds favouring a drier than normal season in the far southeast.
The pattern of seasonal rainfall odds across southeastern Australia is mainly a result of continuing higher than average temperatures over parts of the tropical and sub-tropical Indian Ocean.
The chances of exceeding the median rainfall for the October to December period are between 30 and 40% over much of Tasmania and the far southeastern coastal fringe of the mainland. This means that below-normal falls have a 60 to 70% chance of occurring. So for every ten years with ocean patterns like the current, about six or seven December quarters are expected to be drier than average in these parts of southeastern Australia, while about three or four are wetter.
Over most remaining parts of SA, NSW, Victoria and Tasmania the chances of accumulating at least average rain for the December quarter are between 40 and 60%.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the December quarter, history shows this effect to be moderately consistent across much of southeastern Australia, the main exceptions being eastern NSW and western SA where the effect is only weakly or very weakly consistent (see background information).
There has been further gradual cooling of the equatorial Pacific during the past month, with cool anomalies consistent with a developing La Niña present in central and eastern areas. The 30-day value of the Southern Oscillation Index (SOI) was +6 as at 22nd September. For routine updates and comprehensive discussion on any developments please see the ENSO Wrap-Up.
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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 25th OCTOBER 2007