|WA Seasonal Rainfall Outlook: probabilities for October to December 2007, issued 25th September 2007|
Wetter December quarter indicated for western WA
The Western Australian outlook for total rainfall over the December quarter (October to December), shows a moderate shift in the odds favouring a wetter than normal season in western to central WA. However, it should be noted that the December quarter is a seasonally dry time of year in northwest WA, with heavy rain being uncommon, although tropical cyclones occasionally affect the area during this period.
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.
The chances of exceeding the median rainfall for the October to December period are between 60 and 70% over much of western to central WA (see map). So for every ten years with ocean patterns like the current, about six or seven December quarters are expected to be wetter than average in this part of the State, while about three or four are drier. In the east of WA, the chances of above-median seasonal rainfall are between 55 and 60%.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the December quarter, history shows this effect to be moderately consistent across much of WA (see background information).
There has been further gradual cooling of the equatorial Pacific during the past month, with cool anomalies consistent with a developing La Niña present in central and eastern areas. The 30-day value of the Southern Oscillation Index (SOI) was +6 as at 22nd September. 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 (WST) 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 25th OCTOBER 2007