|WA Seasonal Rainfall Outlook: probabilities for October to December 2008, issued 25th September 2008|
Above average rainfall favoured across Western Australia
The outlook for rainfall over the December quarter (October to December) in WA shows a moderate to strong tendency towards wetter than normal conditions over central western parts of WA. It should be noted though, that the December quarter is a seasonally dry time of year in northwest WA, with heavy rain being uncommon.
The pattern of seasonal rainfall odds across Australia is mainly a result of continued warmth in the central and southeastern Indian Ocean, especially off the west coast of WA.
The chances of exceeding the median rainfall for the December quarter in WA is 70 to 80% in the Gascoyne and western Pilbara regions, grading to 60 to 70% over much of central and western WA, and 50 to 60% for the remainder of the state (see map). This means that for every ten years with ocean patterns like the current, about six to eight years are expected to be wetter than average through the central and western parts while about two to four years are drier.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the October to December period, history shows this effect to be moderately to weakly consistent over much of WA (see background information).
The tropical Pacific Ocean remains ENSO-neutral. There has been some slight cooling at the surface and slightly stronger cooling of the subsurface in the central Pacific recently. The Southern Oscillation Index (SOI) has responded to this cooling and has risen to a value of approximately +17 for the 30 days ending 22nd September. Computer models indicate that neutral conditions are likely to continue for the next few seasons. 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 8.30am to 4.30pm (WST) Monday to Friday by contacting the Climate Services Centre in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 28th October 2008