To enable the public to get prepared for typhoon season, the Hong Kong Observatory from today (June 20) extends its tropical cyclone forecast track from three days to a maximum of five days ahead. The service enhancement results from the considerable improvement in the accuracy of the Observatory's track forecast achieved in recent years. Based on objective verification, the accuracy of the fifth-day track forecast is now comparable to that of the third-day track forecast first introduced in 2003.
When using the forecast track map, members of the public should note that the track of some tropical cyclones could be rather erratic and the forecast positions may deviate from the actual path taken by the storms. In this regard, the Potential Track Area as shown on the map (please see the yellow shaded area in the diagram) indicates the area within which the tropical cyclone will possibly be located with a probability of 70 per cent based on past error statistics. It means that in 10 times of similar track forecasts, about seven times the tropical cyclone centres will be located within the indicated area. The area grows as the forecast period extends. It will be particularly larger beyond 72 hours and is highlighted with lighter shadings on the map.