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.