I have visited Tenerife and Gran Canaria in all of these months and have never had coastal temperatures that dipped much below 20c during daylight hours. However, as I spend a lot of time hill-walking at high altitudes, the temperatures here varying considerably. I remember one day in January 2002 leaving Los Cristianos in very mild but cloudy conditions in the morning only to find myself walking in fairly heavy snow showers on the mountains around Teide. When I returned to
LC later in the day, I sat on my balcony enjoying a drink in warm sunshine!
As Kirsty says, it really depends on where you are staying.