Kerry Emanuel wrote this article. As it turns out, warm water is not the only factor. Also, it depends on wind sheer. In addition, it depends on how high and cold the cloud tops are. Some hurricanes have formed in less than warm water because their cloud tops were high and cold, like Wilma in 2005.
Physical basis of limit calculationsMaximum Potential Intensity based on location. The lowest is the Persian Gulf, where waters are as high as 100 degrees F or 38 degrees C. The central pressure form them is 715 to 736 mb with 265 to 275 knots (305 to 315 mph) winds, which would make it a hypercane.

Of course that will never happen due to dry air and hot sinking air in that region. For Galveston it is 840 to 867 mb with 185 to 205 knots (210 to 235 mph) winds. If a hurricane with 867 mb was to hit us, Houston area would be leveled.
Potential Intensity Estimates for Individual Cities and Regions