SOI message 25th July 2001 (next update 1st August) The 30-day average of the Southern Oscillation Index (SOI) is -0.87 as of the 25th July.
The current series of troughs that have brought rain to some cropping regions will be welcome for those growers who have planted a winter crop, but is probably too late for most of those that haven't. The boost in soil moisture levels will be welcome by all.
The sharp rise in the SOI during June increased rainfall probabilities across most of Queensland at least in the immediate future, however given the larger-scale climate patterns that envelope the SOI, this may only provide a very brief reprieve from the dry. Based on the rapid rise of the SOI during June, the chances of rainfall in the next three months being above the long-term July-September median varies across the state. Probabilities range from 50% in the western Downs to 70% in central and south western Queensland. There is also a region of 30-40% around McKinlay and Richmond shires. However in our key cropping regions this is the driest time of year and the long-term medians are very low.
Over the past few weeks the SOI has steadied around zero, so it is critically important to update the SOI forecast at the end of July.
Review of Climate Forecasts and Information Climate pattern and SOI 'phase'. There is a 50 to 70% probability of July-August-September rainfall totals being equal to or more than the long-term median July-Sept rainfall for most of eastern Australia.
Across Queensland the chance of rainfall in the next 3 months being equal to or above the long term median rainfall in the Darling/Southern Downs is around 60-70%; in the Warrego as high as 80%; in central Queensland 60-70% although reaching to 70-80% along coastal areas; 70% in the inland Burnett regions although dropping to 50-60% along the coast; and 30-40% in southern gulf regions.
Most of eastern NSW has a 60-70% chance of getting at least the long term median July-September rainfall. However along the central coast there are regions with lower rainfall probabilities of between 50 -60% while in the north east probabilities are higher at 70-80%. Most of Victoria and western NSW have a 50-60% probability of rainfall being above the long term median for this period. The far south of W.A and the southern half of South Australia have a 60-70% chance of above-median July-September rainfall totals.
Note that a 70% probability of receiving the long-term median for a location also means there is a 30% probability of not receiving the median for that location. These probability values are simply statements of fact referring to the history of rainfall events for particular locations over the past 100 years. Sea-surface temperatures (SSTs). Sea surface temperatures in the key regions of the eastern equatorial Pacific Ocean are mainly close to long term average (although SST's in the far east are warmer than normal). Interestingly, according to the latest data from the USA/French TOPEX Poseidon satellite mission, a pulse of warm water is travelling towards South America. This equatorial, eastward travelling Kelvin Wave (bulge or pulse of warm water) is due to arrive at the west coast of South America in late July.
The arrival of the Kelvin Wave is expected to cause a warming of the eastern Pacific Ocean similar to an El Niño like sea surface temperature pattern. Kelvin Waves are triggered by westerly wind bursts and are usually seen before the development (within the next year or so) of an El Niño.