[gradsusr] gribmap problem with sub-hour time intervals

[Masters.Steve]

I have a set of grib files produced by WRF using wrfpost that are at sub-hour intervals.  On my outer grid, I am writing out data at 20 minute intervals.  The top of the GrADS control file looks like...

dset ^0901020000_sfcout_arw_d01.grb1f%f2%n200
index ^d01sfc.idx
*  produced by grib2ctl v0.9.12.5p45
dtype grib 255
options template
tdef 19 linear 00Z02jan2009 20mn

I'm using the template option so I can use GrADS to access multiple files in a single session without concatenating them together.  The output from gribmap is listed below...

gribmap -i d01sfc.ctl
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f000000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f002000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f014000  <======
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f010000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f012000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f024000  <======
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f020000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f022000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f034000  <======
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f030000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f032000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f044000  <=====
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f040000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f042000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f054000  <=====
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f050000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f052000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f064000  <=====
 grib1map warning: could not open GRIB file: 0901020000_sfcout_arw_d01.grb1f064000
 grib1map:  opening GRIB file: 0901020000_sfcout_arw_d01.grb1f060000
 grib1map:  reached end of files
 grib1map:  writing the map...

At the "40-minute" point, the hour is incorrectly flipped to the next value.  When I did this same operation against 5-minute output, the error happens as soon as I reach the 30-minute point of the hour.  It seems like some kind of rounding is happening within gribmap when it attempts to resolve the hour part of the time.  Looking at the output from GrADS, it appears to me that the grib index that is created is invalid as I get "bumps" in the time series that indicate data are being plotted at the wrong time (or not at all) in the second half of each hour.

This problem is seen with gribmap 1.9b4, 2.0.a5 and also with the very latest version 2.0a8.

Stephen Masters   masters.steve at ensco.com
ENSCO, Inc.
Melbourne, FL

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