Actually, one thought I had about that would be, perhaps not in frequency, but perhaps in intensity of existing storms.

One of the factors in hurricane intensification (one of, not the sole obviously) is SST. If "global warming", per se, is intended to be a term that refers to the median temperatures globally increasing measurably above historical median temperature levels, then it would be a rational consequence to conclude that the SST levels would eventually change as well. Granted due to the salinity, specific heat of water, sheer volume of water, and so on it would likely take years for the SST to measurably increase.

Still, if by some process SSTs were to increase by even a degree or so above what we would consider baseline "normal" - wouldn't that potentially allow any storms which form normally to have a higher "pool" of energy to work with? If, for example, something unlikely (but possible) such as the magnetic poles flipping due to vortices in the molten iron core of the earth happens, which weakens the magnetosphere to allow cosmic radiation to penetrate to the surface, then the SSTs would more than likely definitely increase, and that would give any storms a bigger feeding ground to work with.

Sorry, I just get my hackles up a bit when I read responses that deal in absolutes. The atmosphere and such is a highly dynamic system that we don't exactly have a perfect understanding of it, and even the concept of "global warming" is something unknown, as there's little ability to watch a biosphere undergo changes on a basis that's rapid enough for us to draw scientific conclusions from.