|Southeastern Aust Seasonal Rainfall Outlook: probabilities for August to October 2007, issued 24th July 2007|
Odds mainly near 50:50 for above normal seasonal rain
For southeastern Australia, the 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.
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 mostly between 40 and 50% across SA, NSW, Victoria and Tasmania, although in parts of eastern and southern SA and far western NSW, the chances are in the 35 to 40% range (see map). 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 four or five August to October periods out of ten are expected to be wetter than average in the southeast, while five or six 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 moderately consistent across much of northern inland NSW, in patches of far northern and southeast SA, parts of western and central Victoria, and northwest Tasmania (see background information). Elsewhere, it is weakly or very weakly consistent.
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 Monday to Friday by contacting the Bureau's Climate Services sections in Queensland, NSW, SA, Victoria and Tasmania at the following numbers:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 23rd AUGUST 2007