The relationship between the maximum wind speeds and potential intensities of tropical cyclones was examined on interannual time scales in the North Atlantic and Western North Pacific basins. Derived from Carnot's principle, the thermodynamic theory for potential intensity (PI) gives an upper bound on the intensity of tropical cyclones given large-scale thermodynamic conditions. Previous studies indicated that wind speeds follow a uniform distribution up until their theoretical maximum (PI), suggesting that a climatic change in PI would affect the intensity distribution of real storms uniformly. Here, we examine if fluctuations in actual wind speeds were indeed governed by fluctuations in PI on interannual time scales. The PI theory was tested by analyzing its relation to actual tropical cyclone wind speeds in the time period 1950-2005. A PI time series was computed in two ways; either at each point along the best tracks of tropical cyclones, or as a basin average using monthly fields. After comparing yearly average time series of wind speed and PI, which were also normalized and detrended, it was found that the two were correlated fairly well. However, the results indicate that actual maximum wind speed is varying with PI less than predicted by the theory by approximately a factor of two.