|Southeastern Aust Seasonal Rainfall Outlook: probabilities for July to September 2008, issued 26th June 2008|
Drier conditions indicated for much of southeast Australia
The seasonal climate outlook for total rainfall over southeastern Australia for the September quarter, shows a shift in the odds favouring drier than average conditions over a broad area covering South Australia, most of Victoria and western New South Wales.
The pattern of seasonal rainfall odds across the southeast is a result of higher than average temperatures in the Indian Ocean surrounding the west coast of WA, and a warming trend in recent months over the equatorial Pacific.
The chances of exceeding the median rainfall over July to September are between about 30 and 40% over the whole of South Australia, the western half of New South Wales and the western two-thirds of Victoria (see map). This means the chances of below normal falls in these areas are relatively high (between 60 and 70%): for every ten years with ocean patterns like the present, about six or seven July to September periods are expected to be drier than average in these areas, while about three or four are wetter.
Over the eastern half of NSW, eastern Victoria, including the Port Phillip Bay area, and all of Tasmania, July to September rainfall totals have a 40 to 50% 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 (near neutral conditions).
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During July to September, history shows this effect to be only weakly consistent across much of Victoria, southeastern SA and Tasmania so this outlook needs to be used with caution in these areas (see background information).
The equatorial Pacific Ocean has been gradually warming during autumn and early winter resulting in the decay of the 2007/08 La Niña event, with neutral conditions currently prevailing. Computer models indicate a continuation of the warming trend, with neutral conditions the most likely outcome during the forecast period. The 30-day value of the Southern Oscillation Index (SOI) was zero as at 23rd June. 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 from 9.00am to 5.00pm local time 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 July 2008