|Northern Aust Seasonal Rainfall Outlook: probabilities for Spring 2007, issued 23rd August 2007|
Generally 50:50 odds for above-normal spring rainfall
The northern Australian outlook for total spring (September to November) rainfall, shows no strong swings in the odds towards either wetter or drier conditions over most of the area. However, there is a moderate swing in the odds favouring a drier than average spring in a region of north-central Queensland, inland from Townsville.
The pattern of seasonal rainfall odds across northern Australia is mainly a result of continuing higher than average temperatures over parts of the south tropical Pacific Ocean.
The chances of exceeding the spring median rainfall are between 35 and 40% in the Upper Carpentaria region of north Queensland, meaning that below-normal falls have a 60 to 65% chance of occurring (see map). So in years with ocean patterns like the current, about six springs out of ten are expected to be drier than average in this part of northern Australia, while about four out of ten are expected to be wetter.
Over the rest of Queensland and the NT, the chances of accumulating at least average rain over September to November are relatively close to 50%.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During spring, history shows this effect to be moderately consistent across most of the NT and Queensland, with the exceptions of the central NT 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, now present in the east. The 30-day value of the Southern Oscillation Index (SOI) was +1 as at 20th August. 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 SEPTEMBER 2007