|WA Seasonal Rainfall Outlook: probabilities for Summer 2007/2008, issued 22nd November 2007|
Increased summer rainfall for western to central WA
The Western Australian outlook for total summer rainfall (December to February), shows a moderate to strong shift in the odds favouring above average totals in the west and centre of the State.
The pattern of seasonal rainfall odds across WA is mainly a result of continuing higher than average temperatures over parts of the tropical and sub-tropical Indian Ocean, especially just west of the central WA coast.
The chances of exceeding the median rainfall for summer are between 60 and 75% over a large area covering much of western to central WA, with the exception of the far southwest and south of the State (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 WA, while about three or four are drier.
Over the rest of WA, the chances of exceeding the three-month median rainfall are between 50 and 60%.
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. (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.
|More information on this outlook is available from 9.00am to 5.00pm (WDST) Monday to Friday by contacting the Climate and Consultancy section in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 17th DECEMBER 2007