A word cyclone is a Word World's response to persistent run-on sentences, especially run-on sentences without punctuation.
Agents are advised to carry spare punctuation on missions likely to generate word cyclones. Punctuation thrown at a word cyclone can calm the cyclone enough to allow agents to carry on with their mission. However, run-on sentences feed the cyclone, and it will continue to be a threat until it runs out of fuel or its host fic is eliminated or repaired.
A word cyclone acts much like a large dust devil, and can become strong enough to lift an agent off the ground or trap him inside the cyclone. This, of course, tends to be highly annoying.