Seasonal Climate Outlook Message for February to May 2010
The bottom line
SOI remains negative David McRae, Qld Climate Change Centre of Excellence, 09/02/10.
Based on a Consistently Negatively SOI phase at the end of January and historical rainfall records, there remains a 40 to 50% chance of getting above median rainfall for February through to the end of April across most of Queensland.
When using a climate forecast you should remember that the probability or percent chance of something occurring is just that - a probability. For example if there is a 70% chance of recording more than 100 mm there is also a 30% chance of recording less than 100 mm i.e. 70-30; 30-70. It does not mean that you will get 70% more than 100 mm or 100 mm plus another 70%.
For those who like to follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during January to March in the following years since 1950; 1952, 1959, 1964, 1973, 1978, 1983, 1987, 1992, 1993 and 1995. Work out your long term average or median rainfall for January to March and see how many times rainfall was well below, well above or close to average during the listed years.
Again it's worth noting that the SOI influence on climate varies across Australia (greatest skill is for eastern Australia) and between seasons (usually greatest skill is for winter, spring and early summer). Therefore users of the SOI are urged to investigate the relationship for their location by using such tools as Rainman StreamFlow.
The 30day average of the SOI as of the 5th February was minus 19.9. While a consistently negative SOI phase at this time of year does not have a major impact on the seasonal outlook, it will be interesting to see if these negative values are maintained over coming months. If the SOI where to remain in strongly negative values (through to the end of autumn) it would be a warning sign for a likely dry winter/spring. For more climate related information, updates on SOI values and the latest outlook map go to www.longpaddock.qld.gov.au
CSIRO have just released a new book titled 'Adapting Agriculture to Climate Change - Preparing Australian Agriculture, Forestry and Fisheries'. The book provides updated climate change scenarios for Australia with the latest climate science. It includes chapters on adapting to climate change, greenhouse gas emissions sources and sinks, as well as risks and priorities for the future. For more information go to www.publish.csiro.au
If anyone is interested I'm happy to give climate presentations at meetings or field days etc. For more information call me on (07) 4688 1459 or e-mail david.mcrae@climatechange.qld.gov.au
The full story
SOI in Consistently Negative SOI Phase David McRae, Qld Climate Change Centre of Excellence, 09/02/10.
Based on a Consistently Negatively SOI phase at the end of January and historical rainfall records, there remains a 40 to 50% chance of getting above median rainfall for February through to the end of April across most of Queensland.
When using a climate forecast you should remember that the probability or percent chance of something occurring is just that - a probability. For example if there is a 70% chance of recording more than 100 mm there is also a 30% chance of recording less than 100 mm i.e. 70-30; 30-70. It does not mean that you will get 70% more than 100 mm or 100 mm plus another 70%.
For those who like to follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during January to March in the following years since 1950; 1952, 1959, 1964, 1973, 1978, 1983, 1987, 1992, 1993 and 1995. Work out your long term average or median rainfall for January to March and see how many times rainfall was well below, well above or close to average during the listed years.
Again it's worth noting that the SOI influence on climate varies across Australia (greatest skill is for eastern Australia) and between seasons (usually greatest skill is for winter, spring and early summer). Therefore users of the SOI are urged to investigate the relationship for their location by using such tools as Rainman StreamFlow.
The 30day average of the SOI as of the 5th February was minus 19.9. While negative SOI values at this time of year do not have a major impact on the seasonal outlook, it will be interesting to see if these negative values are maintained over coming months. If the SOI where to remain in strongly negative values (through to the end of autumn), it would be a warning sign for a likely dry winter/spring. For more climate related information, updates on SOI values and the latest outlook map go to www.longpaddock.qld.gov.au
CSIRO have just released a new book titled 'Adapting Agriculture to Climate Change - Preparing Australian Agriculture, Forestry and Fisheries'. The book provides updated climate change scenarios for Australia with the latest climate science. It includes chapters on adapting to climate change, greenhouse gas emissions sources and sinks, as well as risks and priorities for the future. For more information go to www.publish.csiro.au
Tropical Cyclone Olga was the first cyclone for some time to travel south through inland Queensland. It will be interesting to see if it delivers high rainfall totals but preferably without significant wind damage to buildings and agricultural crops. Cyclones are low pressure systems that form over warm tropical waters and have gale force winds (sustained winds of 63 km/h or greater and gusts in excess of 90 km/h) near the centre. For a cyclone to develop it needs a pre-existing low pressure system or disturbance (trough or surface level low), warm ocean temperatures (greater than 26.5 degrees C), a moist unstable atmosphere (such as suitable for strong thunderstorm development), be at least 500 km away from the equator (to allow for coriolis deflection or spin to develop) and have little change in wind with height (only weak vertical wind shear present to allow for development of the cyclone centre).
TC Larry (March 2006) was the last significant cyclone to impact on Queensland. It crossed the coast near Innisfail in north Queensland as a category 4 cyclone and caused much devastation in that region. A maximum wind gust of 294km/hr was recorded at the Bellenden Ker Tower (CSIRO weather observation site, elevation of 1450m) during TC Larry. Other cyclones to impact on Queensland recently include TC Charlotte during January 2009 (category 1), TC Ellie during February 2009 (category 1) and TC Hamish during March 2009 reached category 5 although it did not cross the coastline.
For a cyclone to be rated as a category 4 it should have wind gusts between 225 to 280km/hr, an average maximum wind speed between 160 to 200km/hr and would usually have an approximate central pressure of 955 to 930hPa. TC Tracey was category 4 (Darwin 1974). For a cyclone to be rated as a category 5 it should have wind gusts in excess of 280km/hr, an average maximum wind speed in excess of 200km/hr and would usually have an approximate central pressure of less than 930hPa. A category 5 cyclone would be extremely dangerous and cause widespread destruction.
For more information on cyclones and warnings, go to the Bureau of Meteorology tropical cyclone warning centre at www.bom.gov.au/weather/cyclone/
Interestingly a key time to watch for the potential development of cyclones is after summer passages of the MJO. Based on its current timing it is looking like the next MJO should cross northern Australia during the second half of February. The MJO is a band of low air pressure which originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Because of the timing of the MJO the phenomenon is also known as the forty day wave. It can be used as an indicator for the timing of potential rainfall events.
The impact of the MJO on rainfall varies between the different seasons and location. For example the MJO has a greater influence on rainfall throughout northern Australia during summer and southern Australia during winter. For more information on the MJO go to www.bom.gov.au
According to the Bureau of Meteorology's annual climate statement which is available at www.bom.gov.au/climate, the annual mean temperature for 2009 across Australia was 0.9 degree C above the 1961-90 average, making it the nation's second warmest year since high-quality records began in 1910. High temperatures were especially notable in the southeast during the second half of the year, with Victoria, South Australia and NSW all recording their warmest July to December periods on record. This is also reflected by 2009 ending Australia's warmest decade on record.
Above average temperatures look set to continue for northern Australia. According to the Bureau there is a 60 to 85% chance of getting above the long-term median maximum temperature during February to April throughout Queensland and the northeast half of the Northern Territory. This pattern is a reflection of the ongoing El Niño event.
Sea surface temperatures throughout the central Pacific remain well above El Niño thresholds. Sub-surface sea temperatures (to a depth of 300 plus metres) throughout the central and eastern tropical Pacific also remain warmer than normal. However, a cooling trend has become evident since mid January which historically has indicated that a return to neutral ENSO conditions may be under way.
Climate models also suggest that tropical Pacific Ocean temperatures may have peaked for this event, though are likely to remain above El Niño thresholds until autumn. This is not unusual as El Niño events tend to run autumn to autumn. Currently none of the surveyed climate models are forecasting any potential return of La Niña like conditions. For more information go to the ENSO Wrap-up from the Bureau of Meteorology www.bom.gov.au/climate/enso
If anyone is interested I'm happy to give climate presentations at meetings or field days etc. For more information call me on (07) 4688 1459
