The tide times for a minor port are estimated by the tide-table user manually calculating using the published time and height differences between a standard port and the minor port. Most tide tables are calculated and published only for major ports, called "standard ports", and only for one year - standard ports can be relatively close together or hundreds of kilometers apart. For detailed information, please refer to the Weather Radar Image website.Tide tables are published in various forms, such as paper-based tables and tables available on the Internet. The Hong Kong Observatory's radar images closest to the time of tropical cyclone analysed position can be shown by pressing the 'Radar Image' button, below which is the 'Time of image' representing the time when radar completes its scan.Since it takes time to receive and process the satellite data as well as generate the image, the time of image may somtimes be different from the time of tropical cyclone analysed position. The infra-red satellite image closest to the time of tropical cyclone analysed position can be shown by pressing the 'Satellite Image' button, below which is the 'Time of image' representing the time when satellite data is completely received at the ground reception system.
These departures are partly due to uncertainties in locating the centre of the tropical cyclone, and partly due to actual short-term variations in the direction and speed of movement of the tropical cyclone itself. Short-term erratic departure of the tropical cyclone from the general direction of movement may occur from time to time.The corresponding radius of 'Potential Track Area' is determined from the statistics in the past years as the mean value. Such real-time positions could deviate from those obtained later through "Best Track Analysis" when more comprehensive sets of observations become available. *Analysed position refers to the positions of tropical cyclones fixed by the Observatory based on observation data available in real time. The size in terms of radius of the 'Potential Track Area' corresponding to different forecast hours are determined from the error statistics of the forecasts issued in past years (updated in 2022) and are as shown in the following table: It will be particularly larger beyond 72 hours and is indicated with lighter shadings on the map. The area grows as the forecast hour increases. Literally, it means that among 10 times of track forecast for similar situations, the tropical cyclone will be centred within the indicated area in about 7 times. By pressing the 'Potential Track Area' button, the probable area within which the tropical cyclone will fall with a probability of 70% will be shown. While the forecast positions and track indicate the most likely future path of the tropical cyclone, they may deviate from the actual path of the storm.Please bear in mind the uncertainty of the tropical cyclone locations as described below in using this function. The user can use the controls on the left of the map to change the area of interest and to zoom into city or even street levels. Detailed information of the tropical cyclone, including latitude, longitude, classification and the maximum sustained wind near centre will be shown when placing the mouse cursor over the analysed or forecast positions.*The tropical cyclone track, analysed positions and maximum sustained wind near centre are based on Hong Kong Observatory's tropical cyclone warning for shipping. No Tropical Cyclone Warning Signal in force
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