The rainy season in Hong Kong is normally between April and September. Rain could be particularly heavy and persistent during May and June, causing severe traffic disruption and on occasions major floods and landslips resulting in casualties.

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. It is independent of other severe weather warnings such as tropical cyclone warning and landslip warning, which will be issued separately where necessary.

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 the public 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. The public will be given clear advice on the appropriate actions to take.

Once issued, the signals are broadcast over radio and television. For your own safety, listen to radio or television announcements for the latest information.

end of the article: http://www.weather.gov.hk/wservice/warning/rainstor.htm