|Northern Aust Seasonal Rainfall Outlook: probabilities for October to December 2007, issued 25th September 2007|
Neutral December quarter rainfall odds for northern Australia
The northern Australian outlook for total rainfall over the December quarter (October to December), shows no bias in the odds towards either a wetter or drier than average start to the northern wet season.
The pattern of seasonal rainfall odds across northern Australia is a result of continuing higher than average temperatures over parts of the tropical and sub-tropical Indian Ocean, and much of the Pacific Ocean (apart from a narrow cool tongue along the equator). These two signals tend to cancel each other across the north of the country, with the Indian Ocean promoting wetter conditions and the Pacific drier ones.
The chances of exceeding the median rainfall for the October to December period are between 50 and 60% over the NT and Queensland, except for a small area in north-central Queensland where the probabilities are over 60% (see map). So for every ten years with ocean patterns like the current, about five or six December quarters are expected to be wetter than average in northern Australia, while about four or five are drier.
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 Queensland and the NT, except in parts of south and southeast Queensland where it is only 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.
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 25th OCTOBER 2007