We drove from Spokane to Seattle on the I-90 once with gusting side winds around 40+ mph. It felt like I was towing on marbles and was a pretty unnerving feeling even when I slowed to well under 50 mph. We pulled over at a truck stop and a semi driver told us that they can sometimes get blown over. Got to the CG and someone there said he has seen some FWs on their side along that I-90 stretch.
It's another case of physics and a simplification is: The lateral force of gusting perpendicular side winds are relatively evenly distributed along the side of a TT. If your axles are approx. 2/3 the way back from front of the TT, every time old man wind pushes hard on the side, the 1/3 behind the axles and the 1/3 in front of the axles cancel out. What's left is the 1/3 portion at the front end portion of the TT and every time a gust pushes hard and suddenly lets go, you will most definitely get moved side to side from the net lateral force. There's no escaping the effect and the longer the TT, the more it will get pushed sideways. Height is also a factor of course.
Every time you get hit by a hard sudden blast of side wind, the driver tries to maintain a straight course on the road by making a steering wheel correction but when the wind suddenly slows down or stops for a moment, you will have over-corrected somewhat which then makes it harder to control. The continual left/right movement of the TT will be harder to control the faster you are going. The only thing you can do is really slow down and better yet, pull over and stop.
Gusting sidewinds are not the same as sway. A tractor trailer pulled by a semi has different dynamics going on because there is a set of wheels close to the front and another close to the rear and aren't a good comparison to a TT, except for maybe height.
