TCAC
TCAC identifies the Tropical Cyclone Advisory Centre responsible for the advisory. The decoded value is kept separate from the communication header and other message identifiers.
TROPICAL CYCLONE ADVISORY DECODER
Decode a Tropical Cyclone Advisory
Decode aviation Tropical Cyclone Advisories into cyclone position, movement, pressure, wind and forecast positions.
Try an example:
TROPICAL CYCLONE ADVISORY
What is a Tropical Cyclone Advisory?
An aviation Tropical Cyclone Advisory provides information about a tropical cyclone that is relevant to international air navigation. The advisory identifies the cyclone and issuing center, gives the observed position and movement, and reports intensity information and forecast positions.
Decoded fields are shown alongside the original advisory, making it easy to check each value against the coded message.
ADVISORY FORMAT
How to read a Tropical Cyclone Advisory
The decoded advisory begins with message identification and issue information, followed by the Tropical Cyclone Advisory Centre, cyclone name, advisory number and observed cyclone position. Movement, intensity, pressure and wind information describe the current state of the cyclone.
Cyclone name and advisory number
The TC field identifies the tropical cyclone by name. ADVISORY NR provides the advisory year and sequence number, allowing successive advisories for the same cyclone to be distinguished.
Observed position
OBS PSN gives the observation time and encoded latitude and longitude of the cyclone center. The position is decoded without replacing the original coordinate group.
Movement
MOV reports the cyclone movement direction and speed. Direction remains in the form carried by the advisory and speed is reported in knots.
Intensity change
INTST CHANGE records the advisory's coded indication of intensity change. The value is preserved as reported rather than expanded beyond the meaning established by the available format evidence.
Pressure and maximum wind
The advisory can report central pressure in hectopascals and maximum wind in knots. These values describe the cyclone state at the advisory time.
FORECAST
Tropical cyclone forecast positions
The advisory provides forecast cyclone positions and maximum winds at successive forecast horizons. The demonstrated format contains +3, +9, +15, +21 and +27 hour forecast fields.
Each forecast position carries its own time and coordinates. Maximum wind is associated with the corresponding forecast horizon rather than the observed cyclone state.
MISSING FORECAST VALUES
Unavailable positions and wind values
A forecast position is not always available. In the documented advisory, unavailable coordinates are represented with slash-filled latitude and longitude fields, and unavailable maximum wind is represented by a slash-filled wind value.
These fields are shown as unavailable rather than being converted to zero or replaced with an estimated position or wind speed.
EXAMPLE
Tropical Cyclone Advisory example
TROPICAL STORM BILL ICAO ADVISORY NUMBER 5
The example identifies Tropical Storm Bill and TCAC KNHC. At 15:00 UTC on 15 June 2021, the cyclone position is reported as N4030 W06200. Movement is northeast at 33 knots, central pressure is 998 hPa and maximum wind is 50 knots.
Forecast entries then give later positions and maximum winds at the defined forecast horizons. The message also carries remarks and the scheduled time of the next advisory.
RELATED WEATHER
Related aviation weather decoders
Tropical-cyclone information can also appear in other aviation weather products. The SIGMET Decoder covers the SIGMET formats documented on that page. Volcanic ash advisories are handled separately by the Volcanic Ash Advisory Decoder.
DECODER COVERAGE
Current decoder coverage
This decoder covers the Tropical Cyclone Advisory format represented by the documented advisory, including observed cyclone data, forecast positions, forecast maximum winds, remarks and next-message time. Other international format variants may differ and are not interpreted unless their structure is established by the available documentation.