The temps here range from very nice (80ish) to the occasional cold snap (40ish), but on average expect days in the low 80's to mid 70's. The nights tend to get into the 60-50 range. There is an amusement park here (Busch Gardens: Tampa) along with various museums, aquariums (Fl Aquarium: Tampa, Mote Marine Aquarium: Sarasota), and a excellent zoo (Lowery Park: Tampa). Plus there are more golf courses here then you can swing a golf club at.
As for diving, I would recommend a spring dive. The water is a constant 72 degrees. Most springs are within a 1-2 hour drive from Tampa. If your looking for a ocean dive, I would probably suggest an east coast dive. I don't think the water in the gulf hasn't cleared up much from all the hurricanes (20-30ft vis). Plus it is starting to get a little chilly out there (currently 74 degrees). Then again, your used to diving there in Cali, so these may be conditions your used to.
Just some ideas, let me know if you have any other questions.
Paul