Lately it has been hot where I live ,and the water is really warm.  The fishing has been tough ,and everyone I've been catching are in deep water. We are supposed to get a heavy cold rain tomorrow. Will that bring the fish back up to the banks? Also how soon after the rain would be a good time to get out?

It could.  Look for areas where streams or run offs enter the lake.  I'd say you can start fishing as soon as the water is rolling in.  The water should be cooler.