Tropical Cyclone Ingrid is currently off the Queensland coast and has been downgraded to a Cat 4. Don't think for a second that just because it's been "downgraded" that it still can't cause mass damage. Tracy was a Cat 4 and look what she did.
Many of you probably know that they name circular storms based on the next letter of the alphabet, Cyclone Delta would follow Cyclone Camilla for instance, and that they retire a really famous name (never another Tracy) but one thing you may not know is that it wasn't until only a few years ago that they started using blokes names.
I think the reason is obvious: "Hell hath no fury like the scorn of a woman". Hands up anyone?
A friend of mine used to live near a beach and down the back of the property was a creek. Call them what you will either Dust Devils or Willie Willies, these used to follow the line of the creek before reaching the ocean and then diffusing.
These things would be no more than 20 feet tall but the winds in them would move at about 90 mph; the whole diameter can't have been anymore than 18 inches as worst.The problem was that local kids would chuck rubbish, tennis balls, water bombs etc into them, so you'd have a swirly mass of crap heading down the creek.
It would be great fun to take to them with a cricket bat and try to hit stuff out of them but being wary because they could cause serious injury (when Little Tim not Big Tim jumped into one he was carried about 10 meters then broke his leg). The swirling crap would be unceremoniously dumped somewhere, and there was this sand bar renowned for the amount of refuse deposited.
I imagine that your classic big circular storms operate the same way, except that the amount of crap required to diffuse them is immenseand would easily include houses, cars, roofing material etc. Therein lies the danger, these things as a collective are cities and townships; wanton destruction isn't something you want to wake up to...
... and in the case of Tracy, a crappy Christmas to boot.