|WA Seasonal Rainfall Outlook: probabilities for July to September 2004, issued 17th June 2004|
Increased falls more likely in parts of southwest WA for September quarter
There is a moderate shift in the odds towards above average three-month falls in small parts of southwest WA, the Bureau of Meteorology announced today. However, for most of the State, the shifts in the odds are too weak to offer any firm guidance as to the most likely outcome for September quarter rainfall.
The current pattern of outlook probabilities has been mostly influenced by recent temperature patterns in the Pacific Ocean.
For the July to September period, the chances of above median rainfall are between 60 and 65% in three small areas in southwest WA; one located northeast of Ravensthorpe, another centred near Narrogin and another between Geraldton and Perth (see map). So in years with ocean patterns like the current, about six September quarters out of ten are expected to be wetter than average in these parts of the State, with about four out of ten being drier.
Across the rest of WA, the chances of exceeding the median seasonal rainfall are between 40 and 60%. 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).
Both the Indian and tropical Pacific Oceans remain mostly warmer than average, although both cooled between April and May. For more detail see the the El Niño Wrap-Up.
The Southern Oscillation Index (SOI) rebounded strongly in May to a value of +13, 28 points above April's 15. The approximate SOI for the 30 days ending 14th June was +7.
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 13th JULY 2004.