|WA Seasonal Rainfall Outlook: probabilities for Summer 2006/2007, issued 23rd November 2006|
Neutral outlook for summer rainfall in WA
The latest seasonal rainfall outlook issued by the Bureau of Meteorology shows a moderate shift in the odds towards below-normal summer (December to February) rainfall for parts of north Queensland. However, across Western Australia the chances of accumulating at least average (median) rain during the coming three months are close to 50%.
The pattern of seasonal rainfall odds across WA is a result of competing effects from higher than average temperatures in both the Pacific and Indian Oceans. The warm Pacific (because of El Niño) biases the climate towards drier than average in northwest WA, while the warm Indian Ocean promotes wetter than average conditions in the west of the State. Hence, the two signals largely cancel each other.
The chances of exceeding the median rainfall for the December to February period, are mainly between 50 and 55% over WA. So in years with ocean patterns like the current, about five summers out of ten are expected to be drier than average over the State, with about five out of ten being wetter.
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).
The Southern Oscillation Index (SOI), negative for the sixth straight month as a result of the El Niño, fell from −5 in September to −15 in October. The approximate SOI for the 30 days ending 20th November was −7.
The current Pacific El Niño pattern, of which the low SOI is but one indicator, is expected to persist for most of the summer. 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, please see the ENSO Wrap-Up.
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|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 20th DECEMBER 2006