Hong Kong tropical cyclone warning signals
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The Hong Kong tropical cyclone warning signals (Traditional Chinese: 熱帶氣旋警告信號) or informally typhoon signals (颱風信號) are a set of signals used to indicate the threat or effects of a tropical cyclone. The Hong Kong Observatory issues the warning signal if a tropical cyclone is centred within 800 kilometres of Hong Kong and may affect Hong Kong later. 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 1 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.
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[edit] History
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.
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.
[edit] Current system
Starting from 1 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 with legal codes and common practices in Hong Kong, once any signals higher than No. 3 are issued, all government agencies will shut down their operations. Schools will immediately cease their sessions, as will the financial markets and a majority of the private sector. Public transit agencies 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 usually gives the city an advance warning of about one to two hours before actually issuing Signal No. 8.
As the system was originally intended to serve as warnings for mariners, the signals are issued based on wind speeds measured around Victoria Harbour. However, the system has also been adopted for use by the public over the years, and with ongoing urbanization, some have come to question the relevance of the warning system's mechanism in this day and age, citing the following reasons:
- The city enters a complete standstill once Signal No. 8 is issued, and economic losses are incurred as a result of disruptions to financial activities.
- An overwhelming majority of buildings in Hong Kong are now built using concrete, and thus are able to withstand substantially higher wind speeds.
- With many tall skyscrapers acting as barriers, wind speeds are slowed, thus minimising the danger that citizens are exposed to.
- The advent of Mass Transit Railway (MTR) has allowed transportation to operate underground, free from weather interferences.
- After being released from work due to an impending storm, many officeworkers treat their time off as an opportunity to go out and socialize, as evident by full restaurants and queues outside cinemas, rather than to go home and ride out the storm, exemplifying the minimal danger a cyclone poses.
[edit] Meaning of signals
The official definitions of the signals are as follows:
| Signal Number |
Signal Name |
Sustained Wind Speed (Kilometre per hour|km/h) |
Gusts (km/h) |
Signal Sign |
Remarks |
|
1 |
Stand-by (戒備) |
N/A |
N/A |
 |
A tropical cyclone is centred within 800 kilometres of Hong Kong and may later affect the territory, or there are strong winds in Hong Kong waters |
|
3 |
Strong winds (強風) |
41 - 62 (Beaufort Force 6-7) |
may exceed 110 |
 |
Strong winds are expected or blowing in the Victoria harbour |
|
8 NW |
Gale or storm force winds |
63 - 117 (Beaufort Force 8-11) |
may exceed 180 |
 |
Gale or storm force winds are expected or blowing from the NW quadrant |
|
8 NE |
 |
Gale Gale or storm force winds are expected or blowing from the NE quadrant | |||
|
8 SE |
 |
Gale or storm force winds are expected or blowing from the SE quadrant | |||
|
8 SW |
 |
Gale or storm force winds are expected or blowing from the SW quadrant | |||
|
9 |
Increasing |
88 - 117, increasing (Beaufort Force 10-11) |
N/A |
 |
Gale or storm force winds are increasing. |
|
10 |
Hurricane (颶風) |
>118 (Beaufort Force 12) |
may exceed 220 |
 |
Hurricane force winds. Eye of typhoon may be passing directly over Hong Kong. |
[edit] Criticism
During Typhoon Prapiroon in August 2006, the Observatory was criticised for deliberately not issuing a signal 8 despite conditions more serious than typical signal 8 typhoons were observed, over 700 trees were blown down and the wind measuring instrument at Ngong Ping was blown away. The theory was that the LegCo was rushing to pass a law regarding the use of covert surveillance on the general public without warrants. If a signal 8 warning was issued, LegCo would have to close its session, delaying the passage of the law. However, the law in Hong Kong does not mention if LegCo closes during Tropical Cyclone Signal No.8. The meeting may continue if conditions warrant. Another possibility is that the Observatory ruled out the No.8 Signal the night before because it was not forecast to come very close to Hong Kong, and did not want to hoist the signal after 'ruling out' the possibility. However, by the next morning, if they hoisted the No.8 Signal then, they would be blamed because employees who just went to work had to come back home. [1] [2] [3]
