|Tas Seasonal Rainfall Outlook: probabilities for Winter 2005, issued 17th May 2005|
Reduced winter rainfall more likely in northern Tasmania
There is a moderate shift in the odds towards below average winter rainfall across northern and parts of central Tasmania, the Bureau of Meteorology announced today. However, the skill of seasonal outlooks (see below) is generally low over Tasmania during winter, so this outlook should be used with caution.
The pattern of winter rainfall odds is a result of above average temperatures in both the Pacific and Indian Oceans. Across southwest WA and southeastern Australia, the warm oceans have a reinforcing effect with the odds tilted in favour of a drier than average winter. However, across southern Queensland and northern NSW, the effects from the two oceans tend to cancel each other, with drier conditions promoted by the warm Pacific and wetter conditions by the warm Indian.
So for the June to August period, the chances of above median rainfall are between 35 and 40% over much of northern Tasmania as well as some areas in the centre of the State (see map). This means that below average falls have a 60 to 65% chance of occurring. Therefore in years with ocean patterns like the current, about six winters out of ten are expected to be drier than average in these parts of Tasmania, with about four out of ten being wetter.
In remaining parts of the State, the chances of above average winter rainfall are between 40 and a little over 45%.
Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During winter, history shows this influence to be generally weakly consistent across Tasmania (see background information).
The Southern Oscillation Index (SOI) has shown a high level of volatility recently with values of 11, zero and 29 for April, March and February respectively. The approximate SOI for the 30 days ending 14th May was 10.
Low SOI values and warming in the Pacific Ocean over the past three months have increased the chances of an El Niño developing in 2005. However, it is still too early to predict what might happen in the Pacific, with any confidence. For routine updates and comprehensive discussion on the latest data relating to El Niño, together with details on what the phenomenon is and how it has affected Australia in the past, 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 from 9.00am to 5.00pm (EST) Monday to Friday by contacting the Climate and Consultancy section in the Bureau's Hobart Office: (03) 6221 2043.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 17th JUNE 2005