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.

The tropical cyclone wind speed probability grids accessed through the tkdegrib/NDFD GRIB2 Decoder currently cover continental U.S. (CONUS) locations only. Data for other areas located throughout the northern hemisphere are available at an ftp site hosted by the National Centers for Environmental Prediction (NCEP). Follow the instructions below for accessing the wind speed probability data for international locations.

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 NDFD tkdegrib/NDFD GRIB2 Decoder. (help pages)
2. Navigate to ftp://ftp.tpc.ncep.noaa.gov/wsp
3. Scroll to the bottom of the list of files for the most recent data and download the .grib2 file to your local machine (right-click > copy to folder). It might be helpful to create a separate folder in an obvious location for wind speed probability data.
4. Open the tkdegrib/NDFD GRIB2 Decoder, click the GIS tab, and navigate to the file you just downloaded.
• Double-click the file.
• Select a time period of interest from the options listed. In most cases, file numbers (#) 121-123 will be the most useful and correspond most closely with the CONUS data. Like the CONUS data, these three files represent the cumulative 120 hr probability of 34, 50, and 64 knot winds.
• Change the path and/or OUTPUT Filename if desired.
• Choose a File Type from the options in the bottom left-hand corner.
• Choose a type of .shp file or leave the default as small polygon.
• Click the Generate button.
5. Add the file to your GIS software.
• Apply symbology according to the ProbWindSpdXN 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.
• When viewing the data in your GIS, note that the grid resolution for this dataset is more coarse than that of CONUS.