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HKWW's TC Policy (Version 2.7)

The following tropical cyclone policy came into effect on May 28, 2008 (Wednesday). Click here to view the first version of the TC policy.

Version 2 edit history:
Version 2.1 edited on June 22, 2008 (Sunday) : Released the 800 km constraint on two issuances per day.
Version 2.2 edited on April 1, 2009 (Wednesday) : Corrected a minor error.
Version 2.3 edited on June 18, 2009 (Thursday) : Added "Forecast Positions".
Version 2.4 edited on August 15, 2009 (Saturday) : Added parameters in "Current Storm Information" and "TC Naming".
Version 2.5 edited on July 12, 2010 (Monday) : Due to time constraint, the number of bulletins guaranteed on a day with TC signals is reduced.
Version 2.6 edited on August 19, 2013 (Monday) : Time of bulletin is updated.
Version 2.7 edited on September 15, 2017 (Friday) : Version includes minor amendment after introduction of the new TC report format.

A. Area of Responsibility (AOR)

A tropical cyclone (with at least tropical depression strength, as defined in Section B) is said to have entered Hong Kong Weather Watch (HKWW)'s AOR whenever when it is in the region bounded by the following lines:

The following shows the AOR of HKWW graphically (click on the picture to view the full-size map):


Tropical cyclone reports are provided only when there exists tropical cyclones within the aforementioned 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:

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.

Please also note that the above table serves as a guideline only; when time is not allowed a slight deviation from the schedule is possible.

2. Format

A tropical cyclone report normally consists of the following parts:

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 enter the 800 km boundary.


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

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: Sat Mar 25 2023 21:03:32 HKT
Last Modified: Fri Jun 03 2022

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