I read an interview yesterday (in German) with a scientist who usually warns of global warming and its consequences but said explicitely that global warming adds either nothing or a very tiny amount to the frequency and strength of hurricanes. In his opinion the data of the hurricanes just do not support the claim.

The damage, however, they do gets larger each decade (enough data on that to be sure) and he says that this increase is manmade but unrelated to global warming. The main contributing factors are:
(1) the changing pattern of settlements (closer to the sea, the rivers, the lakes) puts more people and property in danger zones.
(2) The taking away of natural flooding zones by damming, reducing the percentage of natural soil and all that makes floods getting higher than in former years.

That's not my field of knowledge but I must say he made more sense than the article Little Hawk has linked to.
His opinion in a nutshell: Man is largely responsible for global warming, man is largely responsible for increasing damage by tornadoes, but global warming has close to nothing to do with tornadoes.

Wolfgang