It was indeed pretty hot.
Humidity stayed above 30 % but by Eastern Summer or Asian conditions, it was a fairly dry feeling heat. The following observations are quite subjective and results may vary. You have been warned.
All in all, the merino wool S/S shirt I used ( a Icebreaker Superfine190 weight shirt) stayed quite comfortable through the hike and the hot, sunny, almost shadeless afternoon. It really didn’t perform any less well than the coolmax synthetic shirt I might have worn in similar conditions. The merino wool shirt transported sweat efficiently away from my body and I stayed relatively dry. A capilene or coolmax shirt would have been even more efficient, but the wool did very well, indeed. The shirt had visible moisture in the pits and where my daypack came in contact with the small of my back. I didn’t feel as if I was overheating, I believe the shirt did a stellar job of temp. control through evaporative cooling and through it's inherent insulative abilities---possibly through some homeostatic processes that would need to be scientifically analyzed and described. The shirt, incidentally, is a good UV blocker, there was no tanning or burning. Now here’s the thing, some people don’t like the touch of wool, even a fine soft knit of high quality merino wool. In these hot temperatures, I could feel the wool fiber more ( enough to drive the wool sensitive crazy, I wager) but it never grew to unpleasant proportions for me. In fact, it felt more pleasant against the skin than sweat drenched cotten would. Again, the shirt did end up with pronounced spots of moisture but these dried out within about ½ hour after the end of physical exertion, in the heat----anything would dry out fast at these temps. but capilene would dry out even faster. Natural fibers absorb a certain degree of moisture, synthetics, not so much or not at all.
Final verdict---merino Wool has a very wide comfort range over a broad band of temps. I’d wear LW merino wool in hot weather in the future. I didn’t feel that I sacrificed comfort by going this route, at all, and as an added bonus, I didn’t reek when I went into a local café for a cooling brew and I got a nice look from the waitress who served me. Go, merino!
Incidentally, my temp. read out was a bit on the high side as the watch was sitting on the ground (in partial shade). Official High at 3pm, according to NOAA was 97˚F.