I know what it is like being in a windy location. Like you we are close to a large body of water - the Severn Estuary in our case. We get off-shore breeze and also the prevailing westerlies. Like Chris says, flash can freeze motion. However, at 1/640 sec I suspect you were using a fast enough shutter speed to freeze wind-induced motion. The more likely issue may be getting the centre of focus in the right place - in a breeze/wind your chosen focus centre on the subject may have moved away from the centre of the plane of focus by the time the image is captured. What I do is to take lots of shots (if the subject sticks around long enough). I have got decent enough shots even in quite strong winds doing this. In a stiff breeze you might have to throw away 10 or 20 or more to find a good one, and sometimes none of them will have worked out right, but I find I usually get one that will do. If possible (more with flowers but I'll try it with insects on flowers too) I wait for the flower/foliage to slow down momentarily. I doubt I ever catch it completely at rest in a breeze, but if it is only moving slowly then you have a much better chance of success.
I do the same when shutter speeds have to be slower than I like, which in natural light is quite often. (These days I tend to use flash almost all the time for insects etc, but I use natural light almost all the time for flowers.) With insects etc I take multiple shots even in still conditions with a good shutter speed, because when working hand-held (which I do most of the time now) I get some variation in exactly where the centre of focus falls even in the best conditions, and small differences in where the centre of focus falls can make a big difference to the look of an image.
sparkles by jeff and jan cohen, on Flickr
