Climate Watch Dave McRae 25/07/06
SST Remain Neutral
An interesting feature of recent synoptic weather charts is that the latitude of the sub-tropical ridge of high pressure is further south than normal for this time of year. This has the potential to increase shower activity for Queensland through increased flow of moist easterly winds especially across northern and coastal regions.
The output from ocean/atmosphere forecast models continues to indicate a neutral sea surface temperature (SST) pattern in the central Pacific (rather than an El Nino or La Nina).
However both surface and sub-surface ocean temperatures in the key regions of the central Pacific have shown a warming trend since April. If this warming trend in the central Pacific continues it may adversely impact on our expected spring and early summer rainfall. For more on conditions in the Pacific try the Bureau of Meteorology at www.bom.gov.au/climate/ahead/
Based on a monthly value for June of minus 6.7 the SOI is now in a 'Consistently Negative' phase. At this time of year a Consistently Negative SOI phase gives low rainfall probabilities (less than 30% chance of getting above median rainfall) during July to September throughout most of Queensland.
Low probabilities do not mean there will be no rainfall all it means is that rainfall for July to September will more likely be below median than well above median.
While there were MJO events over the Indian Ocean in April, May and June there was little or no rainfall impact across Australia and the MJO events were weak in amplitude and structure. If the recent timing of the MJO persists at around 30 days then the next passage north of Australia would be expected in late July/early August.
For those seeking rain for dry planted winter cereal crops, a synoptic feature such as a north-west cloud band or trough system is required in conjunction with the passage of the MJO in winter to result in rain. Over the past two weeks the passage of the MJO has triggered monsoonal activity in India and Indonesia.
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/
As of the 25th July the 30 day average of the SOI is minus 8.9. Daily updates on the SOI are available on (07) 46881439 and the latest probability maps are at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au For more information refer to Rainman StreamFlow or contact 132523 or (07) 3404 6999.