|National Seasonal Rainfall Outlook: probabilities for August to October 2007, issued 24th July 2007|
Odds mainly near 50:50 for above normal rain, but drier season indicated in much of Qld
For the southern half of the country, the outlook for total August to October rainfall shows no strong swings in the odds towards either above-normal or below-normal rainfall. In the north of the country though, there are moderate to strong swings in the odds towards below-normal rainfall over most of northern and western Queensland. However, August to October includes the final two months of the northern dry season, so significant rain is uncommon during this period in tropical areas.
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, and this has had a strong influence on the outlook in Queensland.
The chances of exceeding the median rainfall for the August to October period are between 20 and 40% across northern and western Queensland (see map). In parts of eastern and southern SA together with the far western border areas of NSW, the chances are in the 35 to 40% range. However, caution is advised in applying this outlook in SA because of low predictive skill in this part of the country (see below).
So in years with ocean patterns like the current, about two to four August to October periods out of ten are expected to be wetter than average in these parts of Australia, while six to eight out of ten are expected to be drier.
Over the rest of country the chances of accumulating at least average rain for the season are relatively close to 50%.
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) 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.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Lyn Bettio on (03) 9669 4165, David Jones on (03) 9669 4085.|
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 23rd AUGUST 2007