|WA Seasonal Rainfall Outlook: probabilities for October to December 2006, issued 26th September 2006|
Above average falls more likely in parts of western WA
There is a moderate shift in the odds towards wetter than normal conditions for the December quarter (October-December) in a region extending from northwest to central WA, the Bureau of Meteorology announced today. Across the rest of the State, the chances are generally close to 50% for accumulating at least median rainfall during the coming three months.
The pattern of seasonal rainfall odds across WA is mostly a result of higher than average temperatures in the Indian Ocean.
For the total over the October to December period, the chances are between 60 and 65% for above median rainfall in an area extending south from Port Hedland across much of the Pilbara district as well as parts of the Gascoyne, Goldfields and Interior districts (see map). It should be noted though, that the December quarter is a seasonally dry time of year in the Fortescue and West Gascoyne with heavy rain being uncommon.
So in years with ocean patterns like the current, about six December quarters out of ten are expected to be wetter than average across this area in WA, with about four out of ten being wetter.
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).
The Southern Oscillation Index (SOI), negative for the fourth straight month, dropped from −9 in July to a low −16 in August. The approximate SOI for the 30 days ending 19th September was −4.
In addition to the low SOI, the equatorial Pacific has been warming and the Trade Winds have been weak. These ENSO indicators are all consistent with the development phase of an El Niño event, the likelihood of which has risen strongly in the past month. For routine updates and comprehensive discussion on the latest data relating to ENSO, together with details on what the phenomenon is and how it has affected Australia in the past, 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 26th OCTOBER 2006