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 black rainstorm warning on Monday evening, the first of the year, with a trough of low pressure expected to bring heavy rainfall in the coming 24 hours and flooding reported in some areas.The upgrade to the top-tier warning came 45 minutes after the forecaster issued the red signal at 7.50pm.The forecaster first issued an amber warning – the lowest level in the three-tier system – at 7.20pm before upgrading it to red.“Members of the public should stay on high alert and take necessary precautions to reduce their exposure to risk posed by heavy rain and flooding,” the Observatory said.By 9pm, the Drainage Services Department had sent emergency teams to handle flooding at Tsui Sing Road in Tin Shui Wai, Wing Ping Tsuen in San Tin, Ha Chuk Yuen in Yuen Long and Tsang Tai Uk in Sha Tin.