This time from Canadian researcher Robert Scott, as reported here:
In the first public presentation of new research, Scott earlier told the Canadian Meteorological and Oceanographic Society that, since 1970, surface waters heating up in the eastern side of the Atlantic, near the coast of Africa, have widened the spawning grounds for tropical storms and hurricanes by hundreds of kilometers.
Hurricanes only form when the water temperature exceeds a certain temperature (26.5C). Scott's research indicates that a broader area of the Eastern Atlantic is reaching the required temperature. This means hurricanes can form over a larger area, so there tend to be more of them. Furthermore, they start out as tropical storms and travel West, which means that they are now over a broader patch of warm water and have more room to instensify.
Of course, Scott's research has been met with (legitimate) criticism. For example, the number of hurricanes was widely predicted to increase into the new millennium due to natural cycles. Mr. Scott's research will be appearing in Geophysical Research Letters, and hopefully this issue will be addressed there.