|WA Seasonal Rainfall Outlook: probabilities for Spring 2007, issued 23rd August 2007|
Odds favour wetter spring in southwest WA
The Western Australian outlook for total spring (September to November) rainfall, shows a moderate shift in the odds favouring a wetter than normal spring in southwest WA.
The pattern of seasonal rainfall odds across WA is a result of continuing higher than average temperatures over parts of the tropical and sub-tropical Indian Ocean.
The chances of exceeding the median rainfall for the September to November period are between 55 and 60% in southwest WA (see map). So in years with ocean patterns like the current, about six springs out of ten are expected to be wetter than average in this part of the country, while about four out of ten are expected to be drier.
Over the rest of the State the chances of accumulating at least average rain for spring are relatively close to 50%.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During spring, history shows this effect to be moderately consistent in only the southwest and far northwest of the State (see background information). Elsewhere the effect is largely very weakly consistent.
There has been further gradual cooling of the equatorial Pacific during the past month, with cool anomalies consistent with a developing La Niña, now present in the east. The 30-day value of the Southern Oscillation Index (SOI) was +1 as at 20th August. 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 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 25th SEPTEMBER 2007