Displaying TC Wind Speed Probabilities with GIS

Tropical cyclone wind speed probabilities can be quickly and easily converted to various geographic information systems (GIS) formats (.shp, NetCDF, etc.) using the NWS's tkdegrib/NDFD GRIB2 Decoder software. Follow the instructions below for registering and installing the software and then converting the native format to something that can be used in your GIS.

Before working with any NDFD data in a GIS, you must download the tkdegrib/NDFD GRIB2 Decoder tool that allows access to the data. Learn more about this tool by visiting this site: www.nws.noaa.gov/mdl/NDFD_GRIB2Decoder

First register for the software at: www.weather.gov/mdl/NDFD_GRIB2Decoder/register.php

Once registered, download the software from: www.nws.noaa.gov/mdl/NDFD_GRIB2Decoder/download.php

1. Install the tkdegrib/NDFD GRIB2 Decoder. (help pages)
2. Open the tkdegrib/NDFD GRIB2 Decoder and expand the North Hemisphere (AWIPS 227) folder.
• Expand the Days 1-7 folder.
• Click to highlight one of the Prob. Trop. Cyclone Wind fields.
• Click "Download by ftp" or "Download by http" to download the data to your local machine. In most cases, the file(s) of greatest use will be the Cum. Prob. Trop. Cyclone Wind > 34kts or Cum. Prob. Trop. Cyclone Wind > 64kts, which include the cumulative probability (out to 120 hours) of an area experiencing tropical storm force or hurricane force winds, respectively.
3. Once the file(s) have been downloaded, click the GIS tab located in the upper left-hand corner.
• Expand the ndfd folder.
• Expand the nhemi folder.
• Double-click the file(s) you just downloaded.
• Select the time period of interest from the options listed.
• Change the path and/or OUTPUT Filename if desired.
• Choose a File Type from the options in the bottom left-hand corner.
• Choose the Large Polygon option.
• Click the Generate button.
4. Add the file to your GIS software.
• Apply symbology according to the ProbWindSpdN field.
• Choose Quantities, classify (up to 10 classes) and color (up to 10 colors) according to TPC/NHC conventions if desired.
• Use current products posted on www.nhc.noaa.gov for example. It might be a good idea to create a layer file based on NHC conventions for ease of display later.