TC Watch > TC Policy [Refresh] [中文]
 HKWW's TC Policy (Version 3.1) |
The following tropical cyclone policy came into effect on May 20, 2023. Click here to view the first / second version of the TC policy.
Version 3 edit history:
Version 3.1 edited on August 24, 2024: Minor modification on the criteria for issuing full and brief reports.
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:
- Full report - issued for tropical cyclones within a latitude of 10-30 degrees north, and a longitude of 100-135 degrees east.
- Brief report - issued for tropical cyclones outside of the region for which full reports are issued, but still within a latitude of 0-50 degrees north, and a longitude of 100-180 degrees east.
These areas are shown graphically below (click on the picture to enlarge it):
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. A brief report may also be issued if a tropical cyclone is expected to stay within the blue region for less than 24 hours before leaving/transforming into an extratropical cyclone/weakening into an area of low pressure (i.e., when a single full report is expected under the normal criteria).
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.
- *Basic system profile, including
1. *Name and classification of the tropical cyclone;
2. *JTWC number / International number;
3. *Bulletin number;
4. *Time of report, usually the time of issuance of the bulletin;
5. *Time of observation, on which the current and forecast storm information are based;
6. *Position, in terms of latitude and longitude;
7. *Maximum sustained wind speed (1-minute and 10-minute averages) and gusts;
8. Pressure;
9. Past 6-hour movement (direction and speed);
10. Areas currently affected.
- Forecast Track (more on this will be mentioned in Section E)
- Forecast Positions, which provides detailed information about the forecast track shown, including but not limited to latitudes/longitudes and velocities.
- *Overview, which normally describes the overall status of the system. In brief reports, this section will also contain a synopsis of the development of the tropical cyclone.
- TC naming, which includes background information about the tropical cyclone's name
- 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 describes 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
- *Various images provided by other agencies / organizations
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.
- 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), supplemented with kilometres per hour (km/h).
- Pressure: In hectopascals (hPa).
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:
- HKO = Hong Kong Observatory
- JTWC = Joint Typhoon Warning Center
- JMA = Japan Meteorological Agency
- CWB = Central Weather Bureau
- CMA / NMC = China Meteorological Administration / National Meteorological Center
Last Accessed: Sat Mar 22 2025 13:06:49 HKT
Last Modified: Sat Aug 24 2024
