TC Watch > TC Policy [Refresh] [中文]
 HKWW's TC Policy (Version 1) |
IMPORTANT: THIS VERSION HAS BECOME OBSOLETE SINCE MAY 28, 2008 (WEDNESDAY). PLEASE REFER TO HERE FOR THE LATEST VERSION.
The following tropical cyclone policy came into effect on October 1, 2007 (Monday).
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:
- Latitudes: 0 degrees and 50 degrees north; and
- Longitudes: 100 degrees east and 180 degrees.
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:
TC Category |
Wind (knots) |
Winds (km/h) |
Winds (m/s) |
Tropical Depression |
25 - 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 |
Category 1 Typhoon |
64 - 82 |
118 - 153 |
32.6 - 42.5 |
Category 2 Typhoon |
83 - 95 |
154 - 177 |
42.6 - 49.1 |
Category 3 Typhoon |
96 - 113 |
178 - 209 |
49.2 - 58.0 |
Category 4 Typhoon |
114 - 129 |
210 - 239 |
58.1 - 66.3 |
Category 4 Super Typhoon |
130 - 135 |
240 - 249 |
66.4 - 69.1 |
Category 5 Super Typhoon |
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 3 times per day [1] |
| When the Tropical Cyclone Signal Number 1 or 3 is issued, or when a tropical cyclone is located within 800 km of Hong Kong and may post a threat (or other effects) to the territory | Twice 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 19 HKT or 23 HKT.
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:
- Current storm information, including
1. Name of the tropical cyclone;
2. Bulletin number;
3. Time of report, usually the time of issuance of the bulletin;
4. Time of observation, on which the current and forecast storm information are based;
5. Position, in terms of latitude and longitude;
6. Maximum sustained wind speed and gusts, with both information on 1-minute and 10-minute averages;
7. Pressure;
8. Movement (direction and speed);
9. Areas to be affected
- Forecast Track (more on this will be mentioned in Section E)
- Overview, which normally describes the overall status of the system and its position relative to other places
- Movement analysis, which usually states how the storm moved in the past 24 hours and the reasoning of the forecast track
- Intensity analysis, which usually includes the T-number of the system and the changes in the intensity of the tropical cyclone together with reasoning
- Effects on Hong Kong
- Next update, the proposed update time for the next bulletin.
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.
Illustrations are provided as necessary.
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.
- Time: In Hong Kong Standard Time (HKT) which is 8 hours ahead of the Greenwhich Mean Time (= GMT+8).
- Distance: In kilometres (km) and nautical miles (NM).
- Speed: In knots (nautical miles per hour).
- Pressure: In hectopascals (hPa).
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), the hatched area represents the potential track area of the storm during the forecast period. The error radius is different for each tropical cyclone.
F. Abbreviations Used
Commonly-used abbreviations are listed as follows:
- HKO = Hong Kong Observatory
- JTWC = Joint Typhoon Warning Center
- JMA = Japan Meteorological Agency
- CWB = Central Weather Bureau
- CMA = China Meteorological Administration
Last Accessed: Wed Apr 15 2026 23:48:42 HKT
Last Modified: Mon Jul 24 2023
