|WA Seasonal Rainfall Outlook: probabilities for Spring 2005, issued 16th August 2005|
Odds 50:50 for a wetter than average spring in WA
There is an increased chance of a drier than average spring (September to November) in parts of southern Australia, the Bureau of Meteorology announced today. In Western Australia however, the chances of accumulating at least median spring rain are close to 50%.
The pattern of seasonal rainfall odds is a result of continuing above average temperatures in both the Indian and tropical Pacific Oceans.
For the September to November period, the chances of above median rainfall are mainly between 45 and 55% over WA (see map). So in years with ocean patterns like the current, about five springs out of ten are expected to be wetter than median over the State, with about five out of ten being drier.
Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During spring, history shows this influence to be moderately consistent in only the southwest and far northwest of the State (see background information). Elsewhere the influence is largely very weakly consistent.
After reaching a positive value in June (+3), the Southern Oscillation Index (SOI) was steady in July with a value of +1. The approximate SOI for the 30 days ending 13th August was −6.
With the positive values of the SOI, recent cooling of the tropical Pacific and continued neutral cloud and wind patterns across the Pacific, the chances of an El Niño developing in 2005 are slim. 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 15th SEPTEMBER 2005