|WA Seasonal Rainfall Outlook: probabilities for July to September 2005, issued 17th June 2005|
Neutral odds for exceeding average September quarter rain
The chances of accumulating at least average rain over the September quarter (Jul-Sep) are close to 50% across Western Australia, the Bureau of Meteorology announced today.
The pattern of seasonal rainfall odds is a result of above average temperatures in both the Pacific and Indian Oceans. Despite the continued possibility of an El Niño, the Pacific temperatures are not high enough to strongly bias the odds towards below average seasonal rainfall across eastern and southern Australia.
So for the July to September period, the chances of above median rainfall are between 40 and 55% over WA (see map). So in years with ocean patterns like the current, about five September quarters out of ten are expected to be drier than average over the State, with about five out of ten being wetter.
However, it should be noted that July to September is the heart of the dry season across northern Australia and heavy rain is uncommon during this period.
Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During July to September, history shows this influence to be moderately consistent in parts of central and eastern WA, but only weakly consistent across most of the State (see background information).
The Southern Oscillation Index (SOI) has been consistently negative over the past few months with values of 11 and 15 for April and May respectively. The approximate SOI for the 30 days ending 14th June was 14.
Low SOI values and continued warmth in the Pacific Ocean over the past three months, have increased the chances of an El Niño developing in 2005. However, most computer forecasts indicate neutral, though somewhat warmer than average, conditions across the tropical Pacific for the rest of the year. 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, 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 14th JULY 2005