Kind of surprising, seeing such a rapid jump in strength (a) this close to land (usually, a storm close to shore begins to pull in relatively "dryer" air) and (b) moving at such a rapid forward speed. Upper level conditions that push a storm forward at 20 mph are strong enough to produce some sort of shearing effect, which is not conducive to rapid strenghtening.
Must be the fact that the Gulf is just that warm right now, for one thing.