Typhoons may form and affect Hong Kong from May to November. Tropical cyclone advisory bulletins or warnings are issued by the Hong Kong Observatory when a tropical cyclone moves within 800km of Hong Kong.
The Hong Kong Observatory uses numbers 1, 3, 8, 9 and 10 to signify the strength of a tropical cyclone in the vicinity of Hong Kong.
• SIGNAL 1: A tropical cyclone is centred within 800km of Hong Kong and may later possibly affect the territory.
• SIGNAL 3: Strong wind is expected or blowing generally in Hong Kong near sea level, and the wind condition is expected to persist. Winds are normally expected to become generally strong in Hong Kong within 12 hours after this signal is issued.
• SIGNAL 8 AND ABOVE: Gale or storm force wind is expected or blowing in Hong Kong near sea level, which may increase in strength and the conditions are expected to persist. Winds are normally expected to reach gale force generally in Hong Kong within 12 hours after a No. 8 signal replaces No. 3 signal.
The rainy season in Hong Kong is normally between April and September. Rain can be particularly heavy and persistent during May and June, causing traffic disruption and occasionally major floods and landslips.
The rainstorm warning system is designed to alert the public about the occurrence of heavy rain which is likely to bring about major disruptions, and to ensure a state of readiness within the essential services to deal with emergencies.
There are three levels of warning: AMBER, RED and BLACK.
• The AMBER signal gives alert about potential heavy rain that may develop into RED or BLACK signal situations. There will be flooding in some low-lying and poorly drained areas. Key government departments and major transport and utility operators are put on alert.
• The RED and BLACK signals warn of heavy rain which is likely to bring about serious road flooding and traffic congestion. They will trigger response actions by government departments and major transport and utility operators.
Latest tropical cyclone/rainstorm warnings and related announcements are broadcast on radio and TV and posted on the Hong Kong Observatory website (www.hko.gov.hk).