Hong Kong tropical cyclone warning signals
Tropical Cyclone Warning Signals (熱帶氣旋警告信號) or typhoon signals are a set of signals used in Hong Kong to indicate the existence and approximate location of a tropical cyclone. The Hong Kong Observatory issues the warning signal if a tropical cyclone is centred within 800 kilometres of Hong Kong. A very similar system, which is maintained by the Direcção dos Serviços Meteorológicos e Geofisicos de Macau, is used in Macao.
Signals are represented as a set of numbers, symbols and lights.
In the past, the signals were physically hoisted at many locations in Hong Kong; there were 42 signal stations around the territory in the 1960s. However, as radio and television weather reports became increasingly effective, the need to hoist physical signals diminished. The last signal station, Cheung Chau aeronautical meteorological station on Cheung Chau, was decommissioned on 1st January 2002. Accordingly, the observatory has replaced the word hoist with issue in its official terminology, although the phrase "Signal No. __ has been hoisted" is still widely used by the public.
Early days
Beginning in 1884, a combination of drums, balls and cones was hoisted to alert mariners in the harbour of an approaching tropical cyclone. On the other hand, the warning was given to the general public using a typhoon gun. The gun was replaced by bombs in 1907, as the bombs made louder sounds and were considered an improvement. The last typhoon bomb was detonated in 1937.
Numbered system
The first numbered warning signal system was introduced in 1917. The numbers ranged from 1 to 7, with 2 to 5 signifying gale force winds expected from the four quadrants. The system was amended in 1931 with the numbers 1, 5, 6, 7, 8, 9 and 10, with 5 to 8 signifying gales from the four quadrants. The No. 3 Strong Wind Signal was introduced in 1956 as an intermediate warning between the No. 1 Stand By Signal and the gale signals.
Current system
Starting from 1st January 1973, signals 5 to 8 were replaced by 8 NW, 8 SW, 8 NE and 8 SE respectively so as to avoid misunderstanding by the public. This system has been in use ever since.
In accordance to legal codes and common practices in Hong Kong, once any signals higher than 3 are issued, all government agencies will shut down its operations. Schools will immediately cease its sessions, as well as the financial markets and a majority of the private sector. Public transits that operate on the sea or on surface streets and highways will either cease or scale back their operation. In an effort to minimise the disruptions and stress caused by the exodus of office workers from their workplace, the Hong Kong observatory would usually forewarn the city about one to two hours before signal no. 8 is actually issued,
Originally, the signals were intended mainly for the benefits of mariners but have over the years been also adopted for use by the public. However, as Hong Kong modernises and urbanises, there are people who, in recent uears, doubt the suitability of issuing cyclone warnings based on wind speeds within the Victoria Harbour, citing the following reasons:
- The economic losses incurred after a city enters a total standstill
- A massive majority of Hong Kong buildings are now built using concrete, thus able to withstand substantially higher wind speeds.
- With many tall skyscrapers acting as barriers, wind speeds are slowed, thus minimising the harm that citizens are exposed to.
- The advent of Mass Transit Railway (MTR) mostly allow transportation to operate underground, free of weather interferences.
- Many officeworkers, after being released from work due to an impending storm, do not go home, but go out to commercial areas and relax, thus showing the minimal danger a cyclone poses.
Meaning of signals
The official definitions of the signals are as follows:
- No. 1 - This is a stand-by signal, indicating that a tropical cyclone is centred within 800 km of Hong Kong and may later affect the territory.
- No. 3 - Strong winds are expected or blowing in Victoria Harbour, with a sustained speed of 41-62 km/h (kilometres per hour). Gusts may exceed 110 km/h. Winds are normally expected to become generally stronger in the harbour areas within 12 hours after the issuing of this signal.
- No. 8 (NW, SW, NE, SE) - Gale or storm force winds are expected or blowing in Victoria Harbour, with a sustained wind speed of 63-117 km/h from the quarter indicated. Gusts may exceed 180 km/h.
- No. 9 - Gale or storm force winds are increasing or expected to increase significantly in strength.
- No. 10 - Hurricane force winds are expected or blowing. Sustained wind speeds are reaching upwards from 118 km/h. Gusts may exceed 220 km/h.