MIKE MOSS SAYS:      Ken,   Hurricanes and tropical storms are essentially heat engines and, along with other storms act to redistribute heat that would otherwise build up over tropical portions of the earth where the sun's rays are most direct all year long. The manner in which warm and cold airmasses are distributed would then play some role in the movement of fronts and other kinds of storms, as you note, although the connection isn't always especially evident for a given system. As for rainfall, whether to consider them "necessary" is probably kind of a matter of semantics. I tend to think of them as simply a part of nature, and we in North Carolina and the southeastern U.S. in general happen to live in an area where a portion (and in some years a substantial portion, perhaps 15 to 25 percent) of our annual average rainfall can be attributed to the passage of tropical cyclones or their remnants, and so their contributions come to be incorporated into what is considered "normal" over time.