Ken, the Gulf is warmer in summer, sometimes 90deg. water for weeks on end. But it cools off into the 50's in winter, or even into the 40's when it gets really cold (2009 and 2010). Right now it's already down into the 60's, rather early this year because of the cold, rainy November we had.
On the Atlantic side the water temps are more constant because the Gulf Stream flows up there, just off the coast at a constant warm temperature. Today's readings show the water temp off Miami at 78 to 80deg.
In Grand Cayman, where I was diving last week, the water temp was 84deg. and that's where the Gulf Stream gets its warm water.
