|National Seasonal Rainfall Outlook: probabilities for August to October 2008, issued 25th July 2008|
Mixed rainfall odds for late winter to mid spring
The national outlook for total August to October rainfall shows moderate swings in the odds towards below-normal rainfall in central WA and also in a band extending from northern Queensland through to central SA. In contrast, higher than average rainfall is favoured in the southwest of WA.
The pattern of seasonal rainfall odds across Australia 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 Ocean.
The chances of exceeding the median rainfall over the August to October period are between 30 and 40% over much of central WA. Below average rainfall is similarly favoured in a band stretching from central SA to the north of Queensland (see map). This means the chances of below average rainfall are typically between 60 and 70% in these areas
So in years with ocean patterns like the current, about six to seven August to October periods out of ten are expected to be drier than average in these parts of Australia, while three to four are wetter. In addition, confidence is not high through much of SA at this time of year so the outlook needs to be used with caution in this region. In the southwest of WA the chances of exceeding the median rainfall are between 60 and 70% for the August to October period.
Over the rest of the nation, late-winter to mid spring rainfall totals have a 40 to 60% chance of exceeding the three-month median. So the chances of being wetter than normal are about the same as the chances 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 moderately consistent across most of Queensland, the east and north of the NT and the northern inland of NSW. Elsewhere, it is generally weakly consistent, reaching moderate only in patches, including Northern Tasmania (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.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Brad Murphy on (03) 9669 4409, Blair Trewin on (03) 9669 4623,|
Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 27th August 2008