SOI remains Consistently Positive
Dave McRae, Office of Climate Change 13/01/09
Based on the monthly SOI values recorded for November of plus 17.4 and for December of plus 11.6, the SOI has remained in a Consistently Positive phase.
An analysis of historical rainfall records and a Consistently Positive SOI phase at the end of December indicates a reasonable 50 to 70% chance of getting above median rainfall during January through to the end of March across most of Queensland.
The main exception is for the coastal strip running from the Hervey Bay district through to north of Rockhampton where there is a higher 70 to 80% chance of getting above median rainfall during January through to the end of March.
For example Gladstone has an 80% chance of getting above its January to March median rainfall of 415mm, Bundaberg has a 75% chance of getting above its January to March median rainfall of 460mm, Rockhampton has a 70% chance of getting above its January to March median rainfall of 350mm, Toowoomba has a 65% chance of getting above its January to March median rainfall of 310mm, Winton has a 65% chance of getting above its January to March median rainfall of 190mm and Yuleba has a 60% chance of getting above its January to March median rainfall of 190mm.
The 30 day average of the SOI as of 7 January is plus 14.4. You can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service, call (07) 4688 1459.
When using a climate forecast you should remember that the probability or percent chance of something occurring is just that - a probability. For example if there is a 70% chance of recording more than 100 mm there is also a 30% chance of recording less than 100 mm i.e. 70-30; 30-70. It does not mean that you will get 70% more than 100 mm or 100 mm plus another 70%.
For those who like to follow the relationship between the SOI and rainfall patterns in more detail, have a look at what happened in your area during January to March in the following years since 1950 that have had a Consistently Positive SOI phase at the end of December; 1950, 1955, 1961, 1970, 1975, 1988, 1998, 1999, 2000 and 2007.
Find out your average rainfall for January to March and see how many times rainfall was well below, well above or close to average during January to March in the listed years. For more information on historical rainfall data for your region try Rainman Streamflow or www.bom.gov.au
The Madden-Julian Oscillation or MJO last crossed northern Australia during late December/early January. If its timing remains consistent, the next passage of the MJO is likely to occur during early February. Interestingly a key time to watch for the potential development of cyclones is after summer passages of the MJO.
The MJO is a band of low air pressure which originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Because of the timing of the MJO the phenomenon is also known as the forty day wave. It can be used as an indicator for the timing of potential rainfall events.
The impact of the MJO on rainfall varies between the different seasons and location. For example the MJO has a greater influence on rainfall throughout northern Australia during summer and southern Australia during winter. For more information try www.apsru.gov.au/mjo/
The Bureau of Meteorology has recently released the annual Australian Climate Statement for 2008. Key summary points are that the mean Australian annual temperature for 2008 was the 14th warmest on record (0.41Â°C above normal); above average annual rainfall was recorded across the Top End, eastern Queensland, northeast New South Wales and far west parts of Western Australia with average to below average rainfall throughout the rest of Australia including the southern Murray Darling Basin which further exacerbated the drought conditions experienced in that region. For more information go to www.bom.gov.au/climate/current/
According to the Bureau of Meteorology ENSO Wrap-Up (available at www.bom.gov.au/climate/enso) a neutral sea surface temperature (SST) pattern is persisting in the Pacific Ocean.
Of interest however, is that a number of La Nina like characteristics can also be found. For example, the south east trade winds have been stronger than normal across the western half of the equatorial Pacific. This has contributed to the SOI remaining in positive values for the last few months and the inflow of warm moist air across the eastern Australian coastline.
Also subsurface ocean temperatures stretching from the central to eastern Pacific are cooler than normal. This would normally be considered as an early indicator for a developing La Nina SST pattern. This raises the possibility of indicators reaching La Niña levels, even if only briefly, if the cooling persists.
Historically however, our climate year runs from autumn to autumn and it would be unusual for a La Nina (or that matter an El Nino) to develop at this time of year. This is reflected in the output from the reviewed dynamic climate models with the majority forecasting a neutral SST pattern to persist through to the end of the 08/09 summer. For more information on SST's go to www.bom.gov.au/climate/enso/