I swore I would never go to Varadero in winter but circumstances got in the way and lo and behold I was there Dec 3 - Dec 10.
Dec 3 weather was nice, but not hot.
Dec 4 about the same
Dec 5, had to wear long sleeved shirt while on beach
Dec 6 & 7, added t-shirt under my long sleeved shirt
Dec 8, too cold to say on beach, moved to pool which I normally avoid
Dec 9, add rain to above, and needed towels to stay warm, along with t-shirt and long sleeved shirt.
Dec 10, departure day, overcast
The resort doesn;t have a thermometer, but I would think the temps were 15 - 20 most of the week. Combine those temps with strong on-shore winds and it was not pleasant. Forecast for the coming week not looking great either.
Take a sweater. Cubans were wearing coats and long pants.