I've never been up to the observation deck to take pictures, but if it is as windy as the previous poster says, I would bring something to hang on your tripod to keep it from tipping over with your camera on top. Most tripods have a hook on the centerpost---you can probably hang anything on there to weigh it down. I'd get a small drawstring back and a rock, or maybe a bag of sand. Heck, maybe they sell something specifically for that purpose. Maybe try Google'ing it?
Also, I probably wouldn't fully extend the centerpost either. The more parts are extended, the more shaky it's going to be, so if possible just open up the legs but avoid extending the centerpost.
Good luck!