|WA Seasonal Rainfall Outlook: probabilities for November 2006 to January 2007, issued 26th October 2006|
Mixed rainfall outlook for the coming three months
The latest seasonal rainfall outlook issued by the Bureau of Meteorology, shows a moderate shift in the odds towards above normal rainfall for the late spring to mid-summer period (November-January) in parts of northwest and central WA. Across the rest of the State, the chances of accumulating at least median rain during the coming three months are close to 50%.
The pattern of seasonal rainfall odds across WA is a result of higher than average temperatures in both the Pacific and Indian Oceans. The warm Pacific biases the climate towards drier than average in the north, but the warm Indian Ocean is associated with wetter than average conditions across the tropics and in western WA.
The chances of exceeding the median rainfall for the November to January period, are between 60 and 65% in a region extending from the northwest to the interior of WA. So in years with ocean patterns like the current, about six November to January periods out of ten are expected to be wetter than average in this part of the State, with about four out of ten being drier.
However, part of this region encroaches on the West Gascoyne; a district that is seasonally dry during November-January with heavy rain being uncommon.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the November to January period, history shows this effect to be moderately consistent in the far north of WA, but generally weakly consistent elsewhere in the State (see background information).
The Southern Oscillation Index (SOI), negative for the fifth straight month, rose from −16 in August to −5 in September. The approximate SOI for the 30 days ending 23rd October was −14.
The current El Niño conditions, of which the low SOI is but one indicator, are very likely to persist for the rest of 2006, which would qualify it as an official El Niño event. 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 23rd NOVEMBER 2006