I had a wonderful track session last fall that started w/ pouring rain and standing water, eventually went to damp w/ some standing water and finally bone dry
Great learning experience for me. You have to be smooth (very) in the wet.
Soften up your suspension if you have that luxury- dampers, sway bars.
I actually added a couple of psi in the tires for the wet stuff- seemed to help. Ofcourse it's fun being on a wet track when your the only one w/ AWD and street tires