Warning level

The Hong Kong Observatory began issuing warnings for tropical cyclones in 1884, when it began to monitor and report news of tropical cyclones within the South China Sea, and the areas around Guam and Manila. The monitoring efforts later expanded to gathering information from various seafaring vessels. These works were done in conjunction with the Marine Department until 1886. At first, the monitoring and warning services were geared mainly towards seafarers, and not towards the residents of Hong Kong.

The warning system was numerical, consisting of symbols hoisted at various places in Victoria Harbour, in the form of drums, balls, and cones. At first, the signals only gave information as to the cardinal direction from which winds were coming. Revisions of the system in 1904 added alerts as to ordinal wind direction. Until 1917, there were two sets of warning signals, one set with black symbols, and one with red. The black symbols indicated that the tropical cyclone in question was less than 300 miles (480 km) from Hong Kong, while the red symbols indicated a distance of over 300 miles (480 km).

Under the new classification, there will be six classes of tropical cyclones according to their maximum sustained wind speeds near the centre: