Thanks for the tips! Yes, it's the cross-winds that seem to snatch away my tunes. It's least noticible on my Susato C; my Feadog and Oak Ds and Clarke C are just about impossible to play when it's breezy. The question arose because VicTim played an outdoor wedding awhile back, and I had a devil of a time playing. A couple days afterward, while puzzling over the problem, I remembered reading something about problems playing outdoors, so I tested all my pennywhistles outside during Floyd, where I had access to a consistent, strong, unidirectional wind. Sure enough, as long as I played in the lee of my body, all of the whistles played, but only the Susato played into and across the wind (though somewhat erratically!).
I'll look into the Albas and Cooks.
As always, d'cats are the best!