|Southeastern Aust Seasonal Rainfall Outlook: probabilities for May to July 2008, issued 23rd April 2008|
Higher seasonal rainfall favoured in northern NSW
For southeastern Australia, the outlook for total rainfall over May to July shows a moderate shift in the odds favouring a wetter than normal season over northern parts of NSW.
The pattern of seasonal rainfall odds across southeastern Australia is a result of a combination of cooler than average waters across the equatorial Pacific in association with the now weakening La Niña, and warmer than average waters in the Indian Ocean near Australia.
The chances of exceeding the median rainfall over May to July are between 55% and 65% north and east of a line from the northwest corner of NSW to the coast at about Sydney (see map). So for every ten years with ocean patterns like the current, about six May to July periods are expected to be wetter than average in these parts of southeastern Australia, while about four are drier.
Over the rest of the southeast the chances of exceeding the three-month median rainfall are close to 50%: in these areas the chances of it being wetter than normal are about the same as the chances of it being drier. Probabilities of a wet season are just slightly higher for the north and east of Tasmania and for the southern fringe of Victoria west of Wilson's Promontory.
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 over the northeastern half of NSW, Tasmania and a thin band running along the southern fringe of Victoria west of Wilson's Promontory into the southeast districts of South Australia. Elsewhere in South Australia, in eastern and northern Victoria and in the southwestern half of NSW 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-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 Monday to Friday from 9.00am to 5.00pm local time by contacting the Bureau's Climate Services sections in Queensland, NSW, SA, Victoria and Tasmania at the following numbers:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 27th May 2008