Hot, dry September Dave McRae Qld Climate Change Centre of Excellence 19/10/09
According to the Bureau of Meteorology (www.bom.gov.au/) climate summary for Queensland, generally dry conditions where experienced throughout Queensland during July to September. Averaged across the state it was the third driest July to September on record following 1941 as the driest and 1929 as the second driest.
As well as being drier than normal, temperatures experienced during July to September throughout Queensland where also warmer than normal. Area average across Queensland it was the hottest July to September period on record.
This warmer than average trend is likely to continue as there is a 75% chance of getting above long term average October to December maximum temperatures throughout most of southern and eastern Australia. This rises to an 80% chance for southeast Australia, southwest WA, and a small region in central Queensland. For more information go to www.bom.gov.au/climate
These drier and warmer than normal conditions are what is normally expected during an El Nino event. During an El Nino, there is a lower chance of getting above median rainfall during winter, spring and early summer throughout southern and inland eastern Australia.
In the mean time based on a Rapidly Rising SOI phase at the end of September and historical rainfall records, there is a 50 to 60% chance (with a few locations having up to a 70% chance) of getting above median rainfall during October to December throughout most of Queensland.
It will be interesting to see what trend SOI values take as we approach our summer rainfall season. Negative SOI values (say below minus 5) are normally associated with El Nino events. SOI values are currently being influenced by the warmer than average sea surface temperatures to the north of Australia.
The 30day average of the SOI as of the 19th October is minus 6.2. You can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service, call me on (07) 4688 1459 or e-mail firstname.lastname@example.org The latest rainfall probability maps and SOI values are also available at www.longpaddock.qld.gov.au
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%.