This is not an easy question because I don't know of anyone saying that there is an increase in the threat of tropical storms in recent years. If anything, I would say, rather the opposite. Here is why:
We observe an increase of perhaps one degree Celsius as the average global temperature at sea level during the past 30 years. But that is not evenly distributed. The greatest increase is in the north of the northern hemisphere. Then a slight increase in the south of the southern one and no real difference around the equator. Now, the intensity of a storm is in the difference of moisture, temperature and pressure. It is simply thermodynamic!
For example, the reason there are more mid-latitude storms during the winter is that the pole is much colder while the equator remains about the same. If we see an increase of temperature at the poles only, it can only mean that the difference of temperature between that and the equatorial region will be less; hence, less powerful storms.
But then, the atmosphere is three-dimensional and, as far as I know, we are only talking about the temperature at sea level. How is it changing e.g. at the the top of the troposphere? Is anyone measuring that? I think the matter it far too complex to be discussed here or ... by the doomsday prophets who tell us that our carbon dioxide footprint will bring both drought and terrible rainfalls.
