|Northern Aust Seasonal Rainfall Outlook: probabilities for August to October 2009, issued 24th July 2009|
A drier outlook for large parts of Queensland
The northern Australian outlook for total rainfall over the period of August to October, shows moderate to strong shifts in the odds favouring a drier than normal season across much of Queensland and the eastern fringes of the Northern Territory.
The pattern of seasonal rainfall odds across northern Australia is a result of recent warm conditions in the Indian Ocean and warming in the Pacific. The Pacific influence dominates the outlook across the north Australian region, but the Indian Ocean pattern also promotes drier conditions in northern Queensland.
For the August to October period, the chance of exceeding median rainfall is below 40% in a broad area extending over most of Queensland and the far east of the NT (see map). Within this zone, the chances drop to around 20% in north-central Queensland. This means that for every ten years with ocean patterns like the current, about two to four years would be expected to be wetter than average in these parts of northern Australia during this three-month period, with about six to eight being drier.
Over western and northern parts of the Northern Territory and far southeastern Queensland, the chance of a wetter than average season is between 40 and 50%. In other words the chances of above normal falls are about the same as the chances of below normal.
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 August to October, history shows this effect to be moderately consistent across most of Queensland, and eastern and northern NT. Elsewhere, it is generally weakly consistent (see background information).
An El Niño event looks to be developing across the Pacific: the latest outputs from computer models indicate it will reach peak intensity late in the year. 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 +11 for the 30 days ending 21 July. 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 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 26th August 2009