Gregorian/Lunar Calendar
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Physical typhoon signals, originally designed to aid marine navigation, were later widely adopted for general use. The numbered signals were introduced in Hong Kong in 1917 to indicate the direction and wind strength of the tropical cyclone. The system had been revised several times over the decades up to 1973 when the current version was launched. Celebrating the 100th anniversary of numbered typhoon signals, Hong Kong Observatory partners with the Hongkong Post to issue stamps on numbered typhoon signal on 13 June 2017 which aims to enhance public understanding of typhoon signal and raise awareness on typhoon hazards.