My friend called me to tell me her brother (who's a university prof, of course) told her the reason it went to Cat. 4 was because the Gulf was soooo warm. Why was the Gulf sooo warm, you guessed it...global warming.
And it's not like there hasn't been a Cat 4 or warm Gulf waters before. Actually this Summer has been cooler than average. The reason hurricanes get this strong is the lack of shear.