My hot water heater leaks, but only on very cold mornings.?

The heater is a Rheem 40 gal electric. It's in the mudroom that is not within the central h/ac. On very cold mornings there is a wet path across the floor, originating at the base of the water heater. I don't see anything dripping. The htp valve works fine and vents down to the crawlspace. If the tank is failing, why doesn't it drip all the time?