Plotting Western Pacific/Indian Ocean Typhoon Paths in IDV: Joint Typhoon Warning
Abstract: In this
exercise you'll download KML vector products containing past-tracks and
forecast tracks for a storm in the western Pacific, together with a
synoptic satellite image. The vectors can immediately be displayed
in Google Earth or in Integrated Data Viewer. The imagery must be
georeferenced (with a separate MDL exercise) before it can be combined
with these vectors. THIS LESSON IS PROVIDED FOR
EDUCATIONAL PURPOSES ONLY. NO ONE SHOULD ATTEMPT TO RELY ON THESE
ANALYSIS PRODUCTS FOR NAVIGATION OR FOR ANY OPERATIONAL PURPOSES AT SEA.
Preliminary Reading (in
OceanTeacher, unless otherwise indicated):
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.
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
- Save the image file to the same location as
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
|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.
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
|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
|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
|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 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.