Honestly, I'm of two minds when it comes to Dragon's power.
On one hand, I think he has a Weather DF. In order to create a storm, you need more than just wind. You need to be able to manipulate things like air pressure, humidity, dew point, etc.
On the other hand, he could just be a Wind DF. If he knew that a storm was forming on some other island, and if he was powerful enough, he could have brought the storm over using his wind, making it (probably) a bit more powerful along the way.
I don't know. I'm kind of liking the Weather/Climate DF idea, though.