Here's one of the best explanations I've read of how hurricanes form. It's a bit technical, but for the first time I undersand how the heat pump works. Essentially, the evaporating air column pulls a vacuum, which in turn draws more evaporating air into the column. If the temperature gradient and the heat content of the vapor is sufficiently large, the system will increase in size. You need special conditions like low wind shear and very hot water, and some cyclonic winds to make the storm really take organized shape. Powerful and scary.