|Southeastern Aust Seasonal Rainfall Outlook: probabilities for Spring 2007, issued 23rd August 2007|
A mostly neutral outlook for spring rainfall
For southeastern Australia, the outlook for total spring (September to November) rainfall, generally shows no strong swings in the odds towards wetter or drier conditions. However, there is a moderate shift in the odds favouring a drier than average spring in some relatively small parts of SA, Victoria and Tasmania.
The pattern of seasonal rainfall odds across southeastern Australia is a result of continuing higher than average temperatures over parts of the south tropical Pacific Ocean, and also in parts of the tropical Indian Ocean.
The chances of exceeding the median rainfall for the September to November period are between 35 and 40% in the southeast of SA together with parts of western and southern Victoria, and northern Tasmania (see map). This means that below-normal falls have a 60 to 65% chance of occurring. So in years with ocean patterns like the current, about six springs out of ten are expected to be drier than average in these parts of southeast Australia, while about four out of ten are expected to be wetter.
Over NSW and the remaining parts of SA, Victoria and Tasmania, the chances of accumulating at least average rain for spring are relatively close to 50%.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During spring, history shows this effect to be moderately consistent across most of NSW and Victoria, northern Tasmania and scattered parts of eastern and southern SA (see background information). In northern NSW, southern Tasmania and northwest SA, the effect is only weakly or very weakly consistent.
There has been further gradual cooling of the equatorial Pacific during the past month, with cool anomalies consistent with a developing La Niña, now present in the east. The 30-day value of the Southern Oscillation Index (SOI) was +1 as at 20th August. 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 25th SEPTEMBER 2007