New typhoon warnings will be introduced to give a more accurate picture of the strength of an approaching storm. In addition to the present numerical categories, the Hong Kong Observatory will categorise the storms as 'typhoon', 'severe typhoon' or 'super typhoon' according to the sustained wind speed at their centre. 'We used to tell people the exact wind speed at the typhoon's centre,' Observatory director Lam Chiu-ying said yesterday, but they did not seem to get the message and still went out during severe storms. 'By arousing their collective memory of super typhoons attacking Hong Kong, I hope people, especially the younger generation who have never experienced a super typhoon, will learn to protect themselves by staying home or in a safe place.' Typhoons with a maximum sustained wind speed of 150km/h or above will be described as severe typhoons and those with a speed over 185km/h will be dubbed super typhoons. Those with a wind speed lower than 150km/h but higher than 117km/h will be known as plain typhoons. Five storms meeting the super typhoon criterion have struck Hong Kong in the past 50 years. They include Wanda in 1962. The most powerful storm to hit the city, it packed winds of more than 185km/h and left 130 people dead, 53 missing and about 1,300 vessels damaged or sunk. Nine severe typhoons have been identified in that time, including Hagupit last year and Imbudo in 2003. Records show that 15 per cent of typhoons have been of the strength of a severe typhoon and 10 per cent that of a super typhoon. 'We think there's still a chance of a super typhoon hitting Hong Kong under the impact of global warming, even though the number of typhoons approaching the city seems to have decreased significantly,' Observatory assistant director Wai Hon-gor said. He said the new system had been adopted on the mainland and in Japan and the United States. He stressed it did not change the existing system of typhoon warnings using signals 1, 3, 8, 9 and 10. Mr Wai said people would still have to pay attention to the signals but the new categorisation should make them more vigilant by giving them additional information. The Employers Federation of Hong Kong said the No8 signal would remain the trigger for employees to be given the day off.