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HKWW's TC Policy (Version 3.0)

The following tropical cyclone policy came into effect on May 20, 2023. Click here to view the first / second version of the TC policy.

A. Tropical Cyclone Report Issuance Region

Hong Kong Weather Watch (HKWW) issues tropical cyclone reports when a tropical cyclone (with at least tropical depression strength, as defined in Section B) forms or enters the following regions:

These areas are shown graphically below (click on the picture to enlarge it):

HKWW - AOR

A full report is issued if a tropical cyclone is in the blue region, and a brief report is issued if a tropical cyclone is in the red region but outside the blue region.

 

B. Tropical Cyclone Categorization

HKWW uses the following to categorize tropical cyclones based on their maximum 1-minute sustained wind speeds (background colour of each category indicates the colour code used in our TC track map):

TC Category
Winds (knots)
Winds (km/h)
Winds (m/s)
Tropical Depression
22 - 33
41 - 62
11.4 - 17.2
Tropical Storm
34 - 48
63 - 87
17.3 - 24.1
Severe Tropical Storm
49 - 63
88 - 117
24.2 - 32.5
Typhoon (Category 1)
64 - 82
118 - 153
32.6 - 42.5
Typhoon (Category 2)
83 - 95
154 - 177
42.6 - 49.1
Typhoon (Category 3)
96 - 113
178 - 209
49.2 - 58.0
Typhoon (Category 4)
114 - 129
210 - 239
58.1 - 66.3
Super Typhoon (Category 4)
130 - 135
240 - 249
66.4 - 69.1
Super Typhoon (Category 5)
136 or above
250 or above
69.2 or above

 

C. Tropical Cyclone Report - Frequency and Format

1. Frequency

As far as time is allowed, tropical cyclone reports are to be issued with the following frequencies:

Condition(s)
Report Frequency
When the Tropical Cyclone Signal Number 8 or above is issued At least twice per day [1]
When the Tropical Cyclone Signal Number 1 or 3 is issued, or when a tropical cyclone is expected to post a threat (or other effects) to the territory At least once per day [1]
Other circumstances Once per day [2]

[1] Reports may be issued any time within a day. Please stay tuned for the latest information.
[2] Reports are normally issued before midnight Hong Kong Time.

The proposed update time of the bulletins are normally specified near the end of each tropical cyclone report.

2. Format

A full report consists of the following parts; items marked by an asterisk (*) are provided in a brief report.

In a full report, a part on the estimated likelihood of the issuance of tropical cyclone signals by the Hong Kong Observatory will also be included if the storm is expected to come to within 800 km of Hong Kong.

 

D. Units Used

Our bulletin will normally use the following units in various measurements. Some other units may also be used depending on the circumstances.

 

E. The Forecast Track (full report only)

Forecast tracks of HKWW are either drawn after integrating the outputs of different models and agencies, or drawn directly using forecast track given by the Joint Typhoon Warning Center (JTWC). The latter is only used when time is not allowed for thorough analyses of the models.

For tracks drawn after analyses (i.e. not JTWC tracks), we provide forecasts of at most 72 hours ahead if the tropical cyclone is of tropical depression intensity, or at most 120 hours ahead if it is of tropical storm intensity or above. The shaded area represents the 70% probability potential track area of the storm during the forecast period, i.e., there is a 70% chance that the storm is within the shaded region at the corresponding time point.

 

F. Abbreviations Used

Commonly-used abbreviations are listed as follows:

Last Accessed: Tue Apr 23 2024 15:05:37 HKT
Last Modified: Mon Jul 24 2023