TROPICAL storm Becky gave an early weekend break to brokers, fund managers, stock exchange officials and investors as the Number 8 signal forced the closure of the stock exchange yesterday. Money markets, banks, the Hong Kong Futures Exchange and the Chinese Gold and Silver Exchange Society were also closed. It was the first time this year the stock exchange had been closed because of a tropical storm. The last such closure, on July 22 last year, was caused by tropical storm Gary. On July 24, 1991, trading was suspended for part of a day. Yesterday, the Number 8 signal was hoisted at 2.50 am. Some hoped there might be trading in the afternoon, as the storm appeared to be weakening. But in the event the Number 8 signal was not replaced by a Number 3 signal until 3 pm. The market closes whenever the Number 8 signal is hoisted before 8 am. If the signal remains up at noon it remains closed during the afternoon. When the signal is hoisted during the trading day, all activity ceases after 15 minutes. Buy orders are cancelled as soon as the signal is hoisted and sell orders 10 minutes later. The exchange's closure gave investors the opportunity to reflect on the trend of the Hang Seng Index, which fell 180 points to 7,418.11 during the week. The market was overshadowed during the week by growing tensions between the Chinese and British Governments and raids by the Commercial Crime Bureau on offices of the Allied Group.