This story has been made freely available as a public service to our readers. Please consider supporting SCMP’s journalism by subscribing. The Hong Kong Observatory issued a red rainstorm warning on Monday evening and forecast heavy rain for the next 24 hours. The forecaster first issued an amber warning at 7.20pm before upgrading it to red 30 minutes later. Earlier, at 5pm, it warned that the rainfall could reach around 100mm in 24 hours as a trough of low pressure over Guangdong was edging...