|National Seasonal Rainfall Outlook: probabilities for Summer 2007/2008, issued 22nd November 2007|
Increased summer rainfall for eastern & western Australia
The national outlook for total summer rainfall (December to February), shows a moderate to strong shift in the odds favouring above average totals in western WA and eastern NSW into southeastern Queensland.
The pattern of seasonal rainfall odds across Australia is mainly a result of continuing higher than average temperatures over parts of the tropical and sub-tropical Indian Ocean. However, cooler than average temperatures in the equatorial central to eastern Pacific have contributed to the higher chances of a wetter than average summer in eastern Australia.
The chances of exceeding the median rainfall for summer are between 60 and 70% in a large area extending from southeast Queensland across both the northern inland and east of NSW. In WA, a large area covering much of the western half of the state, has chances between 60 and 75% for exceeding the median rainfall over summer (see map).
So for every ten years with ocean patterns like the current, about six or seven summers are expected to be wetter than average in these parts of the country, while about three or four are drier.
Over most remaining parts of the country, the chances of exceeding the three-month median rainfall are between 45 and 60%, except in southwest Victoria where the probabilities drop to around 40% along the coastal fringe.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During summer, history shows this effect to be moderately consistent across much of WA and scattered areas in eastern Australia, but the effect is generally only weakly or very weakly consistent through the centre of the country (see background information).
A late-developing La Niña event is in progress across the Pacific Basin and computer models indicate it will persist at least until the early part of 2008. The 30-day value of the Southern Oscillation Index (SOI) was +11 as at 19th November. 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.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Lyn Bettio on (03) 9669 4165, Blair Trewin on (03) 9669 4623.|
Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 17th DECEMBER 2007