|WA Seasonal Rainfall Outlook: probabilities for November 2007 to January 2008, issued 25th October 2007|
Increased falls for parts of northern & southern WA
The Western Australian outlook for total rainfall over the late spring to mid-summer period (November to January), shows a moderate to strong shift in the odds favouring above average falls in both the southwest and far north of the State. However, it should be remembered that November to January is generally a dry time of year in southwest WA.
The pattern of seasonal rainfall odds across WA is mainly 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 November to January period are mostly between 60 and 65% in southwest WA, and between 60 and 75% in the far north of the State (see map).
So for every ten years with ocean patterns like the current, about six or seven November to January periods are expected to be wetter than average in these parts of WA, while about three or four are drier.
Over the rest of WA the chances of exceeding the three-month median rainfall are between 50 and 60%.
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 the far north of WA, but generally weakly consistent elsewhere in the State. (see background information). So the outlook should be applied with caution in the southwest of WA.
A late-developing La Niña event is in progress across the Pacific Basin and computer models indicate it will persist at least until the early part of 2008. The 30-day value of the Southern Oscillation Index (SOI) was +1 as at 22nd 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 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 27th NOVEMBER 2007