|Southeastern Aust Seasonal Rainfall Outlook: probabilities for Autumn 2008, issued 26th February 2008|
Mixed autumn rainfall outlook for southeastern Australia
For southeastern Australia the autumn outlook for rainfall (March to May), shows a mixed pattern of odds: a wetter than normal season is favoured in eastern SA into western NSW, while below-normal falls are more likely in parts of Victoria and Tasmania. However, the skill of the forecast model is low in southeastern Australia for this time of the year, so this outlook should be viewed with caution.
The pattern of seasonal rainfall odds across southeastern Australia is a result of cooler than average waters across the equatorial Pacific in association with La Niña, and continuing higher than average temperatures in the central to southeastern Indian Ocean, with more influence coming from the Indian Ocean.
The chances of exceeding the median rainfall over March to May are between 60 and 65% in a band extending from central SA to the far west of NSW (see map). So for every ten years with ocean patterns like the current, about six autumns are expected to be wetter than average in this part of the country, while about four are drier. In contrast, areas in northern and central Tasmania together with parts of Victoria's coastal fringe have a 35 to 40% chance of exceeding the autumn median. This means that a drier than normal autumn is a 60 to 65% chance in these regions.
Over the rest of southeastern Australia, the chances of exceeding the three-month median rainfall are between 40 and 60%. 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 southeast Australian rainfall. During autumn, history shows this effect to be only weakly or very weakly consistent (see background information). So the outlooks need to be viewed with caution as the confidence level is low.
A La Niña event is in progress across the Pacific Basin and computer models indicate it is likely to persist until the end of autumn. The 30-day value of the Southern Oscillation Index (SOI) was +20 as at 23rd February. 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 28th March 2008