|WA Seasonal Rainfall Outlook: probabilities for August to October 2007, issued 24th July 2007|
Odds near 50:50 for above normal rain
The Western Australian outlook for total rainfall over late winter to mid-spring (August to October), shows no strong swings in the odds towards either above-normal or below-normal rainfall. Furthermore, August to October includes the final two months of the dry season in northern WA, so significant rain is uncommon during this period in this part of the State.
The pattern of seasonal rainfall odds across Australia is a result of continuing higher than average temperatures over much of the tropical Pacific Ocean, and also in parts of the tropical and sub-tropical Indian Ocean. The Indian Ocean has been warming strongly in recent months.
The chances of exceeding the median rainfall for the August to October period are between 40 and 55% across WA (see map). So in years with ocean patterns like the current, about four or five August to October periods out of ten are expected to be wetter than average over WA, while six or five out of ten are expected to be drier.
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 mostly weakly or very weakly consistent across WA (see background information).
The 30-day value of the Southern Oscillation Index (SOI) rose to +12 during June before settling back to +5 as a final monthly value. Nevertheless, this was the highest monthly value since April 2006 (+15). However, the SOI has continued to fall during July to an approximate 30-day value as at 21st July of −13. ENSO indicators remain mixed in terms of their progress towards a La Niña, despite this being the prediction from computer models. 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 from 9.00am to 5.00pm (WST) Monday to Friday by contacting the Climate and Consultancy section in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 23rd AUGUST 2007