An Observatory chief has defended hoisting the No 8 warning signal for Typhoon Yutu last month, saying the body did not want to convey the 'false message' that the situation was safe. The business sector has called for a review of the typhoon warning system, after damage from Yutu was negligible and the territory was brought to a virtual standstill for 19 hours on July 25. It is estimated the shutdown cost the business community $3.5 billion to $5 billion. Acting Director of the Observatory Lam Chiu-ying said it was necessary to hoist the signal for 19 hours 'under the circumstances and having made the best use of existing technology'. 'I regret the disruptions to the community and economic activities during Typhoon Yutu, but public safety is our paramount consideration,' he said. Critics have asked why the signal was hoisted even though wind speeds over Victoria Harbour failed to reach the required minimum 63km/h set by the Observatory. In a reply to a letter by legislators about the controversy, Mr Lam said Yutu's strong winds came close to and affected the southern part of Hong Kong including Cheung Chau and Shek Kwu Chau for 11 hours. He said the winds were 'practically on the doorstep' of Victoria Harbour, where wind speed is measured to determine if the No 8 signal should be raised . Forecasts indicated a possible change of course for the typhoon, edging Yutu closer and the winds further into the territory, he said. At that stage Yutu was still an intense typhoon with no signs of weakening and posed a serious threat to Hong Kong, he said. 'A change to lower signals would convey a false message to the public that the threat of Yutu to Hong Kong was over. We therefore exercised prudence and kept the No 8 hoisted although the No 8 criteria for wind speed in Victoria Harbour had not yet been reached,' he said.