Seasonal Climate Outlook Message for November 2001 to February 2002
The bottom line
DATED TUESDAY 13TH NOVEMBER.
The recent cloud bands and rain experienced across much of Queensland were part of the expected 30-50day oscillation. It is expected our atmosphere will be next influenced by this oscillation in mid-December. However the actual timing of this phenomena will depend on how 'broad' or 'slow moving' an event it is this time. For those readers interested in this phenomenon we will update the expected timing of its next influence over the following weeks.
While the 30-50day oscillation has been associated with reasonable rainfall totals across much of southern and central Queensland over the last fortnight it is important to remember that it is a tropical phenomenon and influences only the timing of potential rainfall events over southern and central Queensland rather than the actual amount of rain. The 30-50day oscillation information provided is based on experimental research only.
The 30day average of the Southern Oscillation Index (SOI) as of the 13th of November is +2.6. The SOI has continued to slowly increase since a major 'kick' in value in September (from -8.3 at the start of September to +1.6 at the end) and may continue to do so. It is believed that the benefits from this 'kick' in value are still flowing through.
As a result of this increase in SOI value the outlook for the eastern third of Queensland for the November-December-January period has improved with 50-70% probabilities of above-median rain. However for some parts of the western regions of the state probabilities of above median rainfall are lower at only 30-50%.
As always when using probability based forecasts the opposite always applies. For example, if there is a 20% chance of getting above the median rainfall at a location over the next three months there is an 80% chance of getting below it.
This section will be updated on Wednesday 21st November.
The full story
Updated on the 31st October
SOI now in "Consistently Near Zero" Phase
The 30day average of the Southern Oscillation Index (SOI) was -as of the 31st October.
Based on the movements of the SOI over September/October, the regions of the state that have had an improvement in rainfall probabilities include parts of the Mareeba, Herberton, Hinchinbrook, Dalrymple, Thuringowa, Townsville, Whitsunday, Mackay, Mirani, Nebo, Broadsound, Livingstone, Fitzroy, Maroochy, Caboolture, Kilcoy and Esk shires. These areas all have a 60-70% chance or probability of getting above or exceeding the historical median rainfall over November to January.
However areas of lower rainfall probabilities still exist. These include parts of the Chinchilla, Murilla, Cunnamulla, Quilpie, Barcoo, Longreach and Flinders shires where there is only a 30-40% chance of getting or exceeding the median rainfall over the November to January period. The rest of the western half of Queensland also has low rainfall probabilities at only 40-50%.
For the rest of the eastern section of the state there is a 50-60% chance of getting or exceeding the historical median rainfall over the November to January period.
As always when using probability based forecasts the opposite always applies. For example, if there is a 20% chance of getting above the median rainfall at a location over the next three months there is an 80% chance of getting below it.
During the past couple of months, the 30-50 day oscillation influence on Queensland's rainfall has been hard to identify. It appears to have been an unusually broad phenomenon over during the first couple of weeks of October. We can next expect our atmosphere to be influenced by this oscillation in mid-November.
Although strictly speaking it is a tropical phenomenon, it also appears to influence the timing of rainfall events over southern and central parts of Queensland rather than the actual amount of rain.
For those who like to follow historical patterns more closely years in the past that had a 'Consistently Near Zero' SOI phase for September/October include 1995, 1990, 1985, 1984, 1979, 1978, 1968, 1967, 1966, 1961, 1960, 1959, 1958, 1954, 1949, 1937, 1936, 1933, 1931, 1927, 1926, 1919, 1918, 1912, 1909, 1905 and 1904. What was the rainfall like for the next three months in your area for those years?
Of interest for those looking at the longer term outlook, sea surface temperatures in the far eastern Pacific Ocean are cooler than the long term average. However in the key central equatorial Pacific region SSTs are slightly warmer than normal. It is this region that appears to have most influence on Queenslands weather and climate. SSTs in this region have been warming steadily over the past nine months.
While most of the SST prediction models suggest that a warming trend in the central Pacific will continue the question remains as to how much. Some models suggest the Pacific will remain in a "neutral" state but others still are suggesting the potential for this warming to reach El Niño proportions later this year or early into next.
As the SOI tends to follow sea temperature variability in the central Pacific we recommend that those readers looking to get an early indication of seasonal conditions for early next year keep track of any shifts in the SOI value and SST patterns.
If anyone requires more climate related information have a look at the DPI's climate web site www.dpi.qld.gov.au/climate or feel free to contact me through the DPI Call Centre on 13 25 23. A recorded message with the 30day average of the SOI is also available on 46881439.
