|WA Seasonal Rainfall Outlook: probabilities for August to October 2008, issued 25th July 2008|
Mixed rainfall odds for WA for late winter to mid spring
The Western Australian outlook for total August to October rainfall shows that higher than average rainfall is favoured in the southwest of WA, whilst below-normal rainfall is generally more likely in northwest and central WA.
The pattern of seasonal rainfall odds across WA is a result of a continued strong warming trend in the Indian Ocean off the west coast of WA, and a warming trend in recent months over the equatorial Pacific.
The chances of exceeding median rainfall over the August to October period are between 60 and 70% in much of the southwest, grading to between 30 and 40% in central and northwestern parts (see map). It should be noted that areas in the north of WA are typically dry at this time of year.
So, in years with ocean patterns like the current, we can expect about six or seven August to October periods out of ten to be drier than average in northwest and central parts, while three to four are wetter. Conversely in the southwest of WA, around six or seven August to October periods out of ten are wetter than average and three or four out of ten are drier.
For the remainder of the state, the chances of exceeding the August to October median rainfall are generally between 40 and 60% meaning the odds of being wetter than normal are almost the same as the odds of being 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 only weakly consistent through most of WA, reaching moderately consistent only in patches. (see background information).
The 30-day value of the Southern Oscillation Index (SOI) was +3 as at 22 July. Computer models indicate a continuation of neutral conditions across the equatorial Pacific Ocean as the most likely outcome during the forecast period. 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 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 27th August 2008