An Explanation of the Hurricane Research Division's
Archive of Post-Season Processed Hurricane
Flight Level Data

Written by Ed Rahn and Hugh Willoughby

FLIGHTLEVEL data files

All the files in the entire archive are ASCII. The information is contained in the following types of files :

Format conventions

Some useful information on how the data is encoded :

In summary: In the simplest case, for each storm there will be one CTR file holding all the centers used for final processing, one TRK file generated from this file, one POS file generated using the TRK file, and one IDX file that contains information useful for interpreting the data. These files will have names identical except for the extensions.

Life however, is not always simple. For some storms in which flights were at different altitudes, there is more than one track; for example, one track for processing of flights at 700mb and another for flights at 850mb. Other storms have been divided into two or more logical flights, with separate CTR, TRK, POS and IDX files for each. In several cases, especially those of the earlier storms, due to misunderstandings, disk crashes, or whatever, some files have not been preserved. Some TRK files, and a few CTR files, are re-creations of the originals, which have been lost. In such cases, there is explanatory text at the end of the files. For a storm in which the simplest case does not apply, there is a README.ASCII.TXT file in the individual storm subdirectory, explaining the circumstances.

By the way, since there is explanatory text at the end of APF, TRK and CTR files, a program reading one of these cannot simply read until the end-of-file is detected, it must know where the end of the data is. An APF file has 299 data lines; the structure of the following text is fixed - consult any APF file if you need to know what it is. A CTR file has data lines until -9999.90 appears as an end-of-data marker. The zerotime appears in the fourth line after this, in integer month, day and year. The structure of the TRK file is variable. There is one line at the beginning holding the number of splines, the start and end times (seconds relative to the zerotime) and the time interval per spline. There are at least two lines for the latitude coefficients, and two lines for the longitude coefficients; if the spline number is 11 to 15, there are three lines each, if the spline number is 16 to 20 (20 is the maximum allowed) there are four lines each. The explanatory text has the same format as for CTR files; the zerotime is held in the fourth line after the end of the data.

There are also graphical radar composites in existence for many of the storms in this archive, but they are not included in it as of this time. A great deal of work needs to be done to translate these into a standard graphical format. We hope to have them available here in the near future.

Some of the storm subdirectories have further subdirectories called MISC. These hold data used during processing, but which are of absolutely no use to you. Ignore them. There is a subdirectory on the FTP site called CODE which has FORTRAN code that may be of use to you in working with the data in this archive. The file reading subroutines at least may be of interest, and we will have graphical routines to display the data available in the not too distant future. If you have questions about the code or the data in the archive, send them to Bill Barry.

We have tried to check this archive for errors as thoroughly as possible, but if you notice any that have slipped by us, we would appreciate hearing from you.


The project of post-season analysis of storms is the brainchild of Dr. Hugh E. Willoughby, who has supervised the project during its entire lifetime. The early software development was done by Hugh Willoughby, Marcy Chelmow and Jeanne Clos. William Patrick Barry made later additions to the software, and Ed Rahn has done most of the software development since the late Eighties. The track fitting is done using beta splines developed by Dr. Katsuyuki V. Ooyama.

For the first few years Hugh Willoughby did the actual data processing. Ed Rahn took over this in early 1987, and has processed several of the storms dating from before that time. Since Ed's death, no more pass data has been processed awaiting the assignment of someone to this task.