Historical figures taken from Tenerife South Airport
Max.temperature in Tenerife in April is 22 degrees on average with 8 hours of sun a day.
Rainfall in Tenerife in April 8mm over 3 days. Average Humidity is 69%.
In the south of the island the odds of good weather are high (when I say good weather, I mean about 24º but breezy). If you go to the north of the island, you may be somewhat cloudy and cool (about 16 °). If you go up to Teide, after crossing the sea of clouds, it is usually clear. The weather on the summit of the island is usually cool and somewhat windy.
Graph also shows low temperatures and humidity
My advice is to wear clothes with short sleeves (even something lighter) but take sweater or two. Normally the temperature is always reasonable, about a 19 to 24 degrees even in the north, but with the wind factor sometimes can feel cooler. On the subject of rain, sometimes it rains (especially in the north) but rarely all day, and it’s rather more like quick showers.