TYPHOON Sibyl's unusually strong winds and heavy rain led to the unexpected raising of the No 8 signal yesterday morning, the Royal Observatory said. On Monday evening the observatory had said that only a No 3 would be needed, but at 5.10 am yesterday the No 8 was hoisted. Most workers received the morning off and schools were closed. Senior scientific officer Leung Wing-mo said Sibyl was 300 kilometres away and not approaching Hong Kong on Monday night, both of which normally meant a No 8 signal would be unnecessary. 'One characteristic of typhoons compared with cyclones in mid-latitudes [outside the tropics] is that normally the wind is concentrated towards the centre and the wind speed drops rapidly as you move away from the centre,' he said. 'But Typhoon Sibyl deviated from the norm a bit. Its peripheral winds were stronger than average.' Mr Leung said Sibyl also had intense rainbands which were threatening Hong Kong early in the morning - just at the time people would have been heading out for schools and work. Usually the southern part of a typhoon carried more rain than the northern part because the southern winds were laden with moisture from the sea, whereas the northern winds off the land were drier, he said. 'When Hong Kong is in the southern half of the typhoon then we will be exposed to the full intensity of the rain. Typhoon Helen was a case where it headed overland and the rainbands to the south of the centre hit Hong Kong directly,' he said. Typhoon Helen passed Hong Kong on August 12, but most of the rain fell in the following two days, causing nearly 100 landslides including those at Chai Wan and Aberdeen in which three people were killed. Hong Kong was in Typhoon Sibyl's northeast quadrant, but was still battered by severe rainbands and associated higher winds. Sibyl dropped more than 100 millimetres of rain over most of the territory. Isolated areas such as Tai Mo Shan and northern Kowloon received up to 200 mm.