SOI message 22nd August 2001. The 30-day average of the SOI dropped markedly over the past week reaching a value of -8.4 on 22nd August. If it remains this low until the end of the month, it will reduce rainfall probabilities across much of Queensland.
Presently there is a wide range of rainfall probabilities across Queensland for the August/October period, with the main areas of low rainfall probabilities being in NE Qld.
The key point for readers who follow the movements of the Southern Oscillation is to keep track of any shifts in the monthly value of the SOI over the next couple of months. Any substantial fall at this time of year would reduce rainfall probabilities for many areas of the state for the coming summer.
The monthly average SOI for May was -9.9, +2.4 for June and -3.3 for July resulting in a Consistently Near Zero phase for the June/July period.
Review of Climate Forecasts and Information 1st August 2001. Next update 5th September. Seasonal rainfall outlook
For most of eastern Australia there is a reduced chance of getting the median August-October rainfall this year.
The majority of districts in Queensland have only a 40-50% chance of getting median August-October rainfall. However, the probabilities decrease to only 20-30% in the north-east near Charters Towers and Cooktown. Also, the Central Highlands and most coastal districts between Rockhampton and Cape York have only a 30-40% chance of at least median August-October rainfall.
In the drought-stricken regions of the southern Queensland, rainfall probabilities have not improved significantly.
More detailed probabilities can be found in Australian Rainman.
Other States The north-east corner of NSW has the highest probabilities of above-median August-October rainfall with probabilities between 60-70%. However most of the rest of the state, and also Victoria, Tasmania, and Western Australia have equal chances of above or below median falls. In South Australia, the Eyre Peninsula has similarly equal probabilities; however in the northern half of the state, the probabilities are slightly lower (30-40%).
Remember, a 50% chance of above-median rainfall means there are equal chances of it being a wetter or drier 3 months based on the phase of the SOI.
The 30-50 day oscillation
The 30-50 day oscillation is next due to have an influence on Queensland's rainfall towards the end of August. Although strictly speaking it is a tropical phenomenon, it appears to influence the timing of rainfall events rather than the actual amount of rain. This forecast system is based on experimental research only.
Future ocean temperature development
Ocean temperatures in the equatorial Pacific Ocean are in general presently close to the long-term average. However, overall the ocean has warmed significantly over the past 4 months and this can be seen at one of the Bureau of Meteorology's web sites: http://www.bom.gov.au/bmrc/ocean/results/ocean_anals/SEQ_Equator/2001/Jun.gi f
Most of the General Circulation Models that forecast El Nino and La Nina are predicting that we will be in a "neutral" event in 6 months time, although slight warming will take place.
A summary of these model outputs can be found at: http://www.bom.gov.au/climate/ahead/ENSO-summary.shtml Another good website providing an update of conditions in the equatorial Pacific Ocean is: http://www.pmel.noaa.gov/toga-tao/el-nino/forecasts.html#enso
Although we have the necessary preconditions for an El Niño, it remains to be seen whether the oceans will warm sufficiently.