Changes compared to existing Tropical Cyclone tracks

New radii for Tropical Cyclones wind speeds exceeding thresholds and defined per quadrant have been added. See hereafter the additional data descriptors included in the BUFR messages:

We have taken this opportunity to correct  in the new Tropical Cyclone tracks some inconsistent information present in the existing tracks:

• The update sequence number (ecCodes key updateSequenceNumber) is set to 0 (instead of 1).
• The year in BUFR header section 1 (ecCodes key typicalYear) is given using 4 digits, e.g. '2020' (instead of 2, e.g. '20')
• ecCodes key internationalDataSubCategory (BUFRDC section 1 element named DATA SUB-CATEGORY) for HRES is set to 255 (instead of 0) as a missing value. For the ENS remains as set to 0.
• The meteorological attribute significance (ecCodes key meteorologicalAttributeSignificance, data descriptor 8005) is set to 5, instead of 4, for ENS members 51 and 52 (the ENS Control FC and HRES FC). See also WMO=33 code-flag table#CF_008005.

Sample Tropical Cyclones BUFR data

Sample Tropical Cyclone tracks data in BUFR format are available for Tropical Cyclone HEROLD for 19 Mar 2020 at 12UTC, for HRES and ENS.

Both Tropical Cyclone track files with and without wind radii use the same IFS input data. Users should be able to run their existing Tropical Cyclones decoder programs 'as they are' on the tracks data without wind radii. These files should be used as reference. Users have to make sure that their programs run with the tracks with additional wind radii. You may need to make changes to your programs, even if you don't currently plan to use the wind radii.

Testing your Tropical Cyclones decoding software

We recommend users to test their decoding software with the above mentioned sample data, even you do not plan to use the additional radii data included with Tropical Cyclones tracks. ecCodes versions 2.16.0 and above and BUFRDC with WMO tables version 33 have been tested at ECMWF and do work correctly. As the sequence of data descriptors (ecCodes key unexpandedDescriptors) is different in the new Tropical Cyclone tracks, the decoder programs previously used may need to be adapted.

ecCodes users:

If you don't use a recent version (2.16.0 or newer), you will see an error message like:

ECCODES ERROR : unable to find definition file sequence.def in bufr/tables/0/wmo/33/sequence.def::bufr/tables/0/local/0/98/0/sequence.def
Definition files path="/usr/local/apps/eccodes/2.14.0/GNU/7.3.0/share/eccodes/definitions"

You will then need to download, install and use a newer version of ecCodes

BUFRDC users:

If you use BUFRDC and don't have the WMO BUFR tables version 33 installed, you will see an error message like:

BUFR TABLES TO BE LOADED B0000000000000033000.TXT,D0000000000000033000.TXT
STOP BFDEMO: Terminated
open error on /usr/local/apps/bufrdc/tables/000415/B0000000000000033000.TXT

You will then need to download, install and use the WMO BUFR tables version 33. You can point BUFRDC to a different version of the BUFR tables by setting the environmental variable BUFR_TABLES, e.g.:

export BUFR_TABLES=<dir>/bufrdc_tables_wmo_v33/

where <dir>/bufrdc_tables_wmo_v33/ is the directory containing the BUFR tables.

Further documentation

The ecCodes HOME page includes (Fortran, C and python) examples to decode BUFR messages as well as a command line tool to generate sample source code/scripts to decode any BUFR message.

The BUFRDC HOME  page includes the necessary WMO BUFR tables and the BUFRDC user and reference manuals. Note that we do not release new versions of the BUFRDC software any longer. We advise users to migrate their BUFRDC codes to ecCodes.

More information on the computation and explanation of the wind radii will be made available separately.