Seasonal Climate Outlook Message for May to August 2005

The bottom line

Climate Watch (24/05/05)

Lately there has been a large amount of general press coverage given to drought (especially across NSW) and El Niño.

As the regular readers of this column would be aware, there are a number of 'warning signs' that suggest the development of an El Niño in 2005 is a possibility. According to the Bureau of Meteorology El Niño 'Wrap-Up' http://www.bom.gov.au/climate/enso/ the chance of an El Niño developing this year is estimated at around double what may normally be expected.

However this is not a certainty. While sea surface temperatures (SST) in the eastern tropical Pacific remain warmer than normal, the rapid warming of SST that was occurring has levelled out. It will also be interesting to see what impact, if any the recent westerly wind bursts in the western Pacific that occurred after the last MJO have. Strong and maintained westerly wind bursts in the Pacific at this time of year can help trigger the onset of an El Niño.

If there is no further change in SST and atmospheric circulation patterns in the Pacific by the end of June, the chance of an El Niño developing this year is reduced. So the next few weeks will be a key time to monitor any changes.

Prolonged periods of below average rainfall can also occur across eastern Australia without a 'classic' El Niño. For example if warmer than normal SST in the central Pacific persist over the coming months, this can be enough to suppress our normal rainfall (similar to what occurred over last spring and summer).

It is also worth noting that if the 30-day average of the SOI remains in negative values (below minus 3.1) through to the end of this month there will be a corresponding fall in rainfall probabilities across most of the state regardless of whether an El Niño develops this year. As of Tuesday the 24th May the 30-day average is minus 10.9.

So given the physical evidence, our policy remains to recommend a cautious approach when considering the longer-term outlook this year.

To find out more on conditions in the Pacific try the Bureau of Meteorology "El Niño wrap up" at www.bom.gov.au/climate/enso/ or the International Research Institute for Climate Prediction at http://iri.ldeo.columbia.edu/news/monthlyproduct.html or the US Climate Prediction Centre at www.cpc.ncep.noaa.gov/ For the latest sea surface temperature maps have a look at www.cpc.ncep.noaa.gov/products/ or at www.longpaddock.qld.gov.au/

For more specific information for your location refer to Rainman StreamFlow or call the DPI Call Centre on 13 25 23 or (07) 3404 6999.