Let me tell you how I measured 299 deg motion. I have a 20" flat panel monitor on which I'm running GARP 2.1. I can display a high-res satellite image with 1-deg lat/lon lines overlaid. I ran a visible loop from sunrise to early afternoon. On the first image, I lock my cursor onto the location of the small vortex. I then advance the loop slowly to the end, following the vortex along. On the last image, I position my cursor over the vortex. On the bottom of my screen is the heading between the first and last images. That came to 298.7 degrees.
There's no guessing involved, with the exception of finding the center toward the last images, as it's difficult to pinpoint exactly. I don't watch individual thunderstorms, as they won't give the motion of the vortex. They'll trick your eyes, though. If I just watch the loop, it LOOKS like the center is moving due west as of the past 2-3 hours. But when I zoom in and look for the VORTEX, I can see that the thunderstorm on the western side of the vortex has been rotating southward for the past 2-3 hours, giving the illusion that the vortex, itself, is moving westward. The vortex has continued moving WNW.
I would say that the 299 degree estimate is accurate to within 5 degrees, with the margin of error due to the poorly-defined center.
