Baroclinity is, at its most basic, the potential energy between two fluids with different temperatures and densities. When you get that kind of mismatch, the two systems try to mix together and all that potential energy is turned into motion--in this case, wind. "The trough of low pressure that will be sucking in Sandy to the northwest towards landfall will strengthen the storm by injecting 'baroclinic' energy--the energy one can derive from the atmosphere when warm and cold air masses lie in close proximity to each other," says Wunderground's Jeff Masters. What you have right now is a jet stream hovering over the Rust Belt that is really damned cold. Sandy is warm. As the two systems interact, with the hurricane moving west over cooler water, Sandy, unlike most tropical cyclones, will intensify.