Sitting in Chicago yesterday, observing low clouds rushing south on a gusty northerly breeze -- part of the larger circulation of what was left of Hurricane Katrina, hundreds of miles away -- my brother John asked something like, "How do hurricanes get started?" I fumbled for a few minutes talking about some of the ingredients that go into a hurricane -- warm, warm ocean water, the little atmospheric disturbances that sometimes kick off the big storms, and weak wind shear (vertical winds) that allow the storm's circulation to get moving. But I realized, gee, beyond those haphazard scraps, I don't really know.
The question itself is kind of profound, because a quick look through some online references show that while more and more is understood about the process, even supercomputer-wielding climate scientists can't give a final answer to how the storms start. Obviously, hurricanes get lots of attention from serious science; the lack of complete understanding says a lot about how complex weather processes are.
A few "how hurricanes form" links:
--If you love the Socratic method and aren't afraid of brushing up against a little high-level science talk, the National Hurricane Center has an insanely long list of frequently asked questions about the storms. To zero in on hurricane origins, go to the basic definitions page and check out "how do tropical cyclones form?"