|WA Seasonal Rainfall Outlook: probabilities for May to July 2008, issued 23rd April 2008|
Higher seasonal rainfall favoured in northern WA
The Western Australian outlook for total rainfall over the late autumn to mid-winter period (May to July) generally shows a weak to moderate shift in the odds favouring a wetter than normal season.
The pattern of seasonal rainfall odds across WA is a result of continuing higher than average temperatures in the Indian Ocean, and cooler than average waters across the equatorial Pacific in association with La Niña.
The chances of exceeding the median rainfall over May to July are between 50 and 60% across most of Western Australia (see map), so the chances of being wetter than normal are only slightly higher than the chances of being drier. In parts of the Kimberley however, the chances of exceeding the median rainfall are between 60 and 70%. It should be noted though that this is a seasonally dry time of year over northern Western Australia. So for every ten years with ocean patterns like the current, about six or seven May to July periods are expected to be wetter than average in these parts of the Kimberley, while about three or four are drier.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the May-July period, history shows this effect to be moderately consistent in patches through inland Western Australia. Elsewhere the effect is only weakly or very weakly consistent (see background information).
The La Niña event in the Pacific Basin is weakening: computer models indicate a return to neutral conditions over the outlook period of May to July. The 30-day value of the Southern Oscillation Index (SOI) was +5 as at 20th April. 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 8.30am to 4.30pm (WDST) 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 27th May 2008