|WA Seasonal Rainfall Outlook: probabilities for November 2009 to January 2010, issued 23rd October 2009|
Equal chances for above and below average rainfall for much of WA
The WA outlook for rainfall shows equal chances of above or below average rainfall totals for the late spring to mid-summer period (November-January) for much of WA, though wetter than average conditions are more likely in the eastern Kimberley.
The pattern of seasonal rainfall odds across Western Australia is mostly a result of recent warm conditions in the Indian Ocean.
The chances of exceeding the median rainfall for November to January are between 50 and 60% for a large proportion of WA (see map), meaning that above average falls are about as equally likely as below average falls. In the eastern Kimberley, on the other hand, the chances of exceeding the three-month median rainfall are between 60 and 65%. This means that for every ten years with ocean patterns like the current, about six or seven years are expected to be wetter than average in this region, while about three to four years are expected to be drier.
New: An expanded set of seasonal rainfall outlook maps and tables, including the probabilities of seasonal rainfall exceeding given totals (e.g. 200 mm), is available on the "Water and the Land" (WATL) part of the Bureau's website.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the November to January period, history shows this effect to be moderately consistent in parts of northern WA and the southwest land division, but only weakly consistent elsewhere (see background information).
An El Niño event persists across the Pacific Basin, with most leading climate models suggesting tropical ocean temperatures will remain above El Niño thresholds until at least early 2010. El Niño events are usually (but not always) associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia. The SOI is approximately −8 for the 30 days ending 20 October. 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 detailed forecast maps, including the probabilities of seasonal rainfall exceeding given totals, can be found here.
|More information on this outlook is available from 8.30am to 4.30pm (WST) Monday to Friday by contacting the Climate Services Centre in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 24th November 2009