This story has been made freely available as a public service to our readers. Please consider supporting SCMP’s journalism by subscribing. New users who download our updated app get a seven-day free trial. Hong Kong issued a black rainstorm warning signal on Thursday morning, with several areas flooded and authorities cancelling classes and some flights. The Hong Kong Observatory replaced the highest-level signal raised at 7.50am with a red one at 11.10am and then amber at 12.10pm, which was...