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Marine Data Literacy 2.0

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Home > 9. Operational/Synoptic > 9.32 JTWC Cyclones

9.32 Plotting Western Pacific/Indian Ocean Typhoon Paths in Google Earth & IDV: JTWC

NOTIFICATION ON THE WEBSITE:  This is a U.S. government website. JTWC products on this website are intended for use by U.S. government agencies. Please consult your national meteorological agency or the appropriate World Meteorological Organization Regional Specialized Meteorological Center for tropical cyclone products pertinent to your country, region and/or local area.

The information on this site is considered public information unless specifically annotated and may be freely distributed or copied. This information should not be modified in content and then presented as copyrighted material. As required by 17 U.S. Code section 403, third parties producing works consisting predominantly of the material appearing in NMFC/JTWC web sites must provide notice in the subsequent published material that there is NMFC/JTWC incorporated material and data are not subject to copyright protection and can be freely used by the public.  This author, Murray Brown, does hereby notify all MDL users of the above.
1.  Open the JTWC website, and take some minutes to read through the mission and product descriptions.

We're interested in the most recent system being reported on, appearing at the top of the list.  It's named Tropical Depression 26W.  Go through the links to see what's available from the JTWC for this storm.
2.  Experience with JTWC products indicates to this author that the "IR Satellite Imagery" products are not provided with graticules or auxiliary georeferencing files, so they are not very useful to us.  We want the JTWC's "Multispectral Satellite Imagery", and fortunately TR 26W has that type of image.
  • Save the KMZ (labeled here as KML) file to DATA > OCEAN > JTWC as depression_vecs_26w_twentysix_20131016T0900Z_jtwc.kmz
  • Save the image file to the same location as depression_msimage_26w_twentysix_20131016_jtwc.jpg

Of course, you will use the latest data for your own work.  But make sure to save only images and data where a Multispectral image is provided.
3.  The KMZ file doesn't need to be unzipped.  Just double-click on it and it will open in Google Earth (GE).
4.  When you zoom closer in GE, the finer details appear, and station information.
5.  Look in the menu on the left side of GE to see that an enormous number of features are contained in the "KML" file.  Each or all of these can be viewed with ease.

In the GE universe of possibilities, you can combine this data product with many other marine or meteorological data products.
6.  Now here is our image file, viewed in a graphics editor.  It isn't georeferenced yet, so we can't view it in GE yet.
7.  Run Integrated Data Viewer (IDV).
8.  Select DATA CHOOSERS > GENERAL > FILES > GOOGLE EARTH FILES.  Then navigate to the KMZ file and click ADD SOURCE.
9.  You'll immediately see that the product contains forecast and previous track date.  We don't have time to go through all of these, but let's take a quick look at forecast storm tracks.

Select WP26 STORM TRACK and DRAWING CONTROL.  Then click CREATE DISPLAY.
10.  Look closely and you'll see the trajectory on the left, south of Japan.
11.  In IDV use SHIFT-CURSOR to zoom into the area of the trajectory.
12.  On the dashboard, loo at the DISPLAYS tab and you'll find that the trajectory is listed as a POLYGON.

Double-click on the POLYGON item.
13.  This opens a PROPERTIES window.  Widen the line, as you see here, to 3.  Also change the line color if it isn't easily visible.

You can return here to make other changes later.
14.  The forecasted trajectory is easily visible now.
15.  Now go back to the dashboard and select the second part of the FORECAST product, named PLACEMARKS.  Select also LOCATIONS, and then click CREATE DISPLAY.
16.  You can see some of the PLACEMARKS, which seem to be projected times and peak winds at the location.
17.  To improve visibility, select DISPLAY > DECLUTTER.  Then also change the DISPLAY COLOR to WHITE.
18.  The PLACEMARKS now appear to be much more complex, as we saw with GE, above.
19.  To eliminate the overlapping labels and other messy places in the graphic, go back to DISPLAY and click DECLUTTER.

You can also experiment with the DENSITY slider control to get a good map.  Remember, however, that every time you move the slider, you must uncheck and re-check DECLUTTER to enforce the setting.
20. Using the settings you see in Panel 19, the author gets this final map.
21.  But how to interpret the circles?
  • The winds within the smallest "circle" are at least as strong as the value printed just to the right of the center point. 
  • Larger circles, when present, surround lesser windspeeds, moving outward, as appropriate:  <110 knots, <10 knots, <85 knots, <65 knots, <55 knots, <45 knots, <35 knots (but never larger than the central value).
  • Points with a windspeed value but no circle, will obviously experience these winds but no exact spatial dimensions are currently in the JTWC shapefile
22. A FINAL WORD OF CAUTION.  If you are not a certified meteorologist, then do not use the above methods and products to "publish" or circulate tropical storm analyses as if they were your own invention.  Make certain that everything you make here is clearly identified by you as having come from a specific other source, namely the Joint Typhoon Warning Center.  And be very careful that you date your files and products so that older version can be scrapped and do not cause problems.  These are wonderful data products and software systems, but they can easily be abused and cause difficulties if you do not take care to educate users about their origins and purposes.