Warmer ≡ more energy ≡ more energetic storms.

I've read a few different studies on the relation between global warming and hurricane intensity, and they all seem to be reaching similar conclusions. You cannot blame any individual storm or event on global warming. But you can identify and explain some trends. Like, Warming world blamed for more strong hurricanes:

A massive global increase in the number of strong hurricanes over the past 35 years is being blamed on global warming, by the most detailed study yet. The US scientists warn that Katrina-strength hurricanes could become the norm.

Worldwide since the 1970s, there has been a near-doubling in the number of Category 4 and 5 storms – the strength that saw Hurricane Katrina do such damage to the US Gulf coastline late in August 2005.