|WA Seasonal Rainfall Outlook: probabilities for August to October 2009, issued 24th July 2009|
Wetter than normal conditions favoured in southwest Western Australia
The WA outlook for total rainfall over the late winter to mid-spring period (August to October), shows a moderate shift in the odds favouring a wetter than normal season across in most southwest WA.
The pattern of seasonal rainfall odds across Western Australia is a result of recent warm conditions in the Indian Ocean and warming in the Pacific, with the greater influence coming from the Indian Ocean.
For the August to October period, the chance of exceeding median rainfall is between 60 and 65% over most of the southwest WA (see map). This means that for every ten years with ocean patterns like the current, about six years would be expected to be wetter than average in these parts of WA during this three-month period, while about four would be expected to be drier.For the remainder of the state, the chance of a wetter than average season is mainly between 45 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 generally weakly consistent across much of WA, reaching moderate only in patches, including in parts of the southwest (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 from 8.30am to 4.30pm (WST) Monday to Friday by contacting the Climate Services Centre in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 26th August 2009