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Tropical Cyclones

Tropical Cyclones can occur over the Western Pacific and the South China Sea throughout the year but there are approximately ten times as many in September as in February.  Gales (winds of 63 km/h or more) due to tropical cyclones have affected Hong Kong as early as May and as late as December.

Tropical cyclones in the area are often very severe, with winds frequently exceeding 150 km/h. Boat owners are advised to take early action whenever a tropical cyclone warning signal is hoisted, since weather and sea conditions might prevent any action at a later stage.

Tropical Cyclone Warning Signals

http://www.weather.gov.hk/informtc/tcsignal.htm

From 1884 until 1917, a drum, ball and cone system was used to inform mariners in the harbour of the existence and close proximity of a tropical cyclone. On land, explosive charges were detonated, to warn the public that gale force winds were expected. The last ‘typhoon bomb’ was exploded in 1937.

The first numbered signal system was introduced in 1917. The signal numbers were from 1 to 7 with the numbers 2, 3, 4 and 5 signifying gale force winds from each of the four quadrants. These signal numbers were amended in 1931 and again in 1956, to become 1, 3, 5, 6, 7, 8, 9 and 10. The numbers 5 to 8 were then used to signify gale force winds from each of the four quadrants but this was often misunderstood and on 1^st January 1973, these numbers were replaced by 8NW, 8SW, 8NE, and 8SE. This system, which was originally intended for mariners, has been in use ever since and has also been adopted for general use in Hong Kong.

More information on the system can be found on the back of a Tropical Cyclone Plotting Map, copies of which can be obtained free of charge from the Hong Kong Observatory and from the public enquiries sections of all district offices.

When a tropical cyclone is located within the area bounded by latitudes 10 degrees North and 30 degrees North and longitudes 105 degrees East and 125 degrees East, warning bulletins are issued every 6 hours, or every 3hours if sufficient information is available. Details of the current tropical cyclone warning signals and the actions to be taken are as follows:

No 1: This is the standby signal, indicating that a tropical cyclone is centred within 800km of Hong Kong and may later affect the territory

Action If you are planning an outing, remember that there is a tropical cyclone near Hong Kong, which may affect your plans later. Listen to radio and TV broadcasts on the progress of the storm. Make sure you will have enough time to secure your property for typhoon conditions if a higher signal number should be hoisted.

No3: Strong winds are expected or blowing in Victoria Harbour with a sustained wind speed of 41-62 km/hr. Gusts may exceed 110 km/hr. Winds are expected to become stronger in the harbour area about 12 hours after the hoisting of this signal

Action Secure boats and moorings for typhoon conditions. Listen to radio and TV announcements for further information about the storm.

No 8NW:
No 8SW:
No 8NE:
No 8SE:
Gale or storm force winds are blowing in Victoria Harbour with a sustained wind speed of 63-117 km/hr from the quarter indicated. Gusts may exceed 180 km/hr.

Action Complete all precautions now before gales commence.

No 9: Gale or storm force winds are increasing or are expected to increase significantly in strength.

Action: Stay in a safe place.

No 10: Hurricane force winds are expected or blowing. Sustained wind speeds are reaching upwards from 118 km/hr. Gusts may exceed 220 km/hr.

Action Same as for signal No 9.

Remember that if the eye of the typhoon passes directly over Hong Kong, there may be a temporary lull lasting from a few minutes up to several hours. Do not relax your guard, as there will be a sudden resumption of violent winds from a different direction. Remain where you are if protected and be prepared for destructive winds.

Tropical Cyclone Warning Services

Information and warning of tropical cyclones are contained in most broadcasts from domestic broadcasting stations and Hong Kong’s radiotelephony broadcasts for aviation.  These bulletins contain all available information about the tropical cyclone and when gales are expected, the domestic broadcast stations broadcast at 15-minute intervals throughout the day and night.

Descriptive terms of wind speeds, classification and winds associated with tropical cyclone warning signals are as follows:

Classification of tropical cyclone according to maximum sustained winds 

 Winds associated with tropical cyclone warning signals 

The Strong Monsoon Signal is used to warn of winds in excess of 22 knots due to the winter or summer monsoons.  These winds may sometimes reach 38 knots or more in very exposed places.

BEAUFORT WIND SCALE