Tenerife, the largest of the Canary Islands, is blessed by great weather all year round. It has subtropical oceanic climate, and the weather is mostly mild and sunny most with some rainfall in the winter.
The only drawback of the winter are shorter days. In December Tenerife gets 6 hours of sunshine. However the temperature of the sea and air is both around 20°C. However beware that on elevations (such as Teide observatory of Izaña) the weather is much colder. Snow and even frost are possible there. January and February are the coldest month of the year.
Like at Mediterranean, it rains more in the winter, when islands are influenced by Atlantic depressions. December is the rainiest month, but on the average it rains for just 4-6 days per month.