Hurricane Tracks and Steering Winds

In this task we will use GrADS to plot hurricane positions (or hurricane track) together with wind vectors at a particular time. We will also do a little study of the steering wind for hurrricanes

The hurricane track data can be obtained from this Unisys archive.

The wind vectors are obtained from the reanalysis data. With the coarse resolution of the reanalysis data (and model) we will not find an intense hurricane in the reanalysis data. But we will see cyclones in the reanalysis data, nearly at the position of the hurricane as given in the track data. The author of this page is ignorant about the extent to which hurricanes have been assimilated into the reanalysis data.

Download hurrgrads.tar.gz.
Read the file "Readme" inside.

There are some GrADS scripts to make the following plots:

A simple plot using hurtrk_lite.gs.

A deluxe plot using hurtrk_dlx.gs and mywinds2.gs.

Your task is to:
  1. Download the track data for the 1999 hurricane "Gert". Easy.
  2. Repeat the above plots, but for Gert and winds on 0z19sep1999. Easy.
  3. Extend your deluxe plot in 2. to overlay the wind vectors at both 850 mb (in white) and 500 mb (in green), and include the hurricane track. See the User's Guide entry about Display options. You will probably need to to set "arrscl" and colors manually in the overlay. But the User's Guide failed me on the details. The "inurl" method to seach the archives via Google came to the rescue. Hint: search for words color and vector. Not trivial.
  4. Use wgrib to dump to u and v winds on 0z19sep1999 into text files. Write a simple program (python or perl are recommend) the gives an average value of the wind components in a 6x6 grid box around the hurricane. This means the hurricane is in the center of a square array 36 points. Those averages give you the steering wind components. Calculate this steering wind for 850mb and 500mb. Forecast a position for Gert on 0z20sep1999, based on your calculated steering wind. Compare with the observed position at that time. Which steering wind gives the most accurate position? Challenging.

    You are not required to make a plot of anything for this last part of the task. A table of the results could be sufficient. Post the scripts you used to make your calculations.