Reading the signs
If, during a Sydney-hobart, we know that there is low pressure to the south and a cold front approaching, there are a number of things to watch for. A roll or cigar-shaped cloud is a clear indication of an approaching front. There may well be thunder on its leading edge and a close eye on the water will show the approaching squall line.
Statistically, close to Sydney, the buster is most likely to arrive late afternoon, being driven by high temperatures and the effect of the mountains. Further south the timing is less influenced by the land and more by the speed of the depression and cold front.
This does make it important to pick up synoptic charts as well as GRIB files to understand if a front is approaching. Bear in mind that GRIB files tend towards average wind speeds and so the actual wind on the front will be considerably greater than the wind indicated behind the front. Local coastal forecasts give a good expectation of maximum wind while coastal observations position the front.
Although the roll cloud is the best indicator, it is not always there and I have been caught out with no real sign of the approaching change before the spinnaker was wrapped around the forestay. We had managed to miss all the other signs of its approach, and the subsequent beat in strong wind was not much fun!