SOI continues to fluctuate. Dave McRae (20/07/07)
The 30day average of the SOI as of the 20th July is minus 8.2. While somewhat disconcerting the drop in value of the SOI since the end of June will have little impact if the SOI returns to positive values before the end of the month.
However if the SOI remains in negative values rainfall probabilities for coming months will drop. It is also worth remembering that for most of Queensland, August and September have the lowest long term average rainfall totals.
Currently there is a 50 to 70% chance of getting median rainfall for July through to the end of September throughout most of Queensland. The exception is for parts of the central north where there is a lower 40 to 50% chance of getting median rainfall.
The generally useful rainfall that was recorded during mid June coincided with the last passage of the MJO. Based on its current timing the MJO is next expected in early August. The MJO is a band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events (but not amounts). For more information try www.apsru.gov.au/mjo/