The BOM says this about METAR/SPECI:
The wind speed, given in knots (KT), is the mean value over the sampling period. The maximum gust during the sampling period is reported when it exceeds the mean speed by 10 KT or more. It is indicated by the letter G which is followed by the gust value. In Australia, mean wind is sampled over 10 minutes and a 2 minute period is used for maximum gust.
What is the source of the wind information used in the OP's question?