This work was supported in part by the NOAA Hurricane Forecast Improvement Project (HFIP), Office of Naval Research Grant N000140910526 and the National Science Foundation Grant ATM-0840651. The computing was performed at the Texas Advanced Computing Center. We are thankful for the comments provided by three anonymous reviewers for improving the manuscript.
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The background error is estimated from 24- and 12-h forecast differences over the previous month using the National Meteorological Center (NMC) method (Parrish and Derber 1992). The calculation is performed using the gen_be utility in the WRF data assimilation package with control variable option 5.