Climate Watch 05/07/05
Above average rain was recorded across the southern half of Queensland and most of NSW for June providing a welcome respite from persistent dry conditions. For example at Miles the provisional Bureau of Meteorology recording for June was 153 mm compared to a long term average of 38 mm. Historically the highest recording at Miles for June was 196 mm in 1912.
The recent rainfall pattern appears to have been associated with the fairly unusual far-southern displacement of the sub-tropical ridge of high pressure over recent months. The latitude of this high pressure belt moves north and south on a roughly 11 year cycle. There is some evidence that suggests that it is correlated with solar activity which currently is at a minimum.
The recent southerly placement of the high pressure belt has allowed our prevailing south-easterly winds to push moisture across eastern Australia. DPI&F have a prototype climate forecast system under development that includes the sub-tropical ridge as key component.
Currently the MJO has low amplitude and is somewhat hard to discern. This is due to strong monsoon activity over India, SE Asia and convection over the South China Sea. Satellite imagery indicates MJO is currently over Andaman Sea which means it should have an influence on our region next week (week starting 11/07).
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) across much of Queensland.
For more information on the MJO including its location try www.apsru.gov.au/mjo/ or for more technical blurb try www.bom.gov.au/climate/tropnote/tropnote.shtml
The monthly value of the SOI rose from minus 11.7 for May to plus 0.5 for June placing the SOI in a 'Rapidly Rising' phase. With the rise in value of the SOI most of the state has above a 50 to 60% chance of getting median rainfall for July through to the end of September.
For example at Miles there is a 70% chance of getting above 80 mm for July through to the end of September, Emerald has a 70% chance of getting above 55 mm, Roma has a 65% chance of getting above 75 mm, and Gympie has a 60% chance of getting above 115 mm.
It will be very interesting to see if the recent upward trend of the SOI is maintained over coming weeks or if it is just a short-term fluctuation. As we have stated regularly, for there to be an overall widespread and maintained improvement in conditions across the state, it would help if the SOI went into positive values for a couple of months at least. The last time the SOI was in a "Consistently Positive" phase was for one month in March 2004 and before that was in March 2001.
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.