We were there in December and the journey from Southampton was rather cold and rough but once we arrived in the canaries it was lovely. Visited Vigo on the return journey and it was freezing - ice and frost everywhere. Again on the way back to Southampton sea was very rough and it was reported as a force 7 gale. If you can do a fly cruise we would recommend it.
Yes. The weather was lovely and warm, quite warm enough to swim in the ship's outdoor pool. There can be wet weather but we were lucky. The main problem can be the seas on the way to the Canaries for, at that time of the year, there can be storms which can lead to a "bumpy" ride. Overall, these islands (and Madeira) are worthwhile Winter destinations from Europe and really the only ones close at hand.
We went to the Canaries this winter leaving on 27 Nov. The sea state was not too bad and we have had worse at better times of the year. The weather, although warm, was unusually cloudy and therefore not hot, except for one day when we had glorious sun and temperatures around 25C. We have been to Tenerife before in January and been swimming in the sea so you usually get good weather. At least you avoid the dismal weather in UK in the run to Christmas.
We were there in December and the weather was fine, not hot but pleasantly warm. shorts and T shirt weather. Apart from one night ,when it was a bit turbulent, the sea was generally calm. As we had never been there before we had nothing to compare with but several people did grumble that it was not as hot as usual for that time of year and they did not aquire the tan they hoped for.