For holidaymakers, that's probably the best course of action. South Gran Canaria is sunny for well over 300 days every year and often has blue skies even when the forecasts show cloud for the island as a whole.
South Gran Canaria exists in a bubble of sunshine caused by the Trade Winds and the high central mountains. More on that here.
On the rare occasions when we do get actual weather (rain, wind, even snow at the top, etc), it is caused by several different variables and is difficult to predict.
Rain normally comes from the North Atlantic but occasionally it comes up from the south and rarely from the east and west. Cold air flows down from Northern Europe while hot air and dust blow over from the Sahara.
But the forecast says rain
Rain happens, but most of it falls in the mountains and in the north. Most online weather forecasts just show an average for the whole island without taking into account its microclimates.
If your holiday isn't for a week or so, then take all forecasts with a pinch of salt as nobody knows how things will pan out. Wet patches often fade out or change direction before they arrive, or only affect the north of the island.
Even if you are unlucky enough to get rain on the beaches, don't worry as it normally blows over in a couple of days.
Accurate weather forecasts
Large weather websites don't do a good job in Gran Canaria because they show the average weather and don't take into account the local variations that keep the resorts sunny.
The best success of information are local: The Spanish language AEMET weather service is good at forecasting general conditions, but not so hot on local weather. El Tiempo does a better job of local forecasting and its app is really useful.
The Gran Canaria Blog has a superb archive of weather for each month of the year: Really cool for checking what the weather has been like for the last few years.
Or you can visit the Gran Canaria Info weather forecast page. We don't even try to forecast the weather more than a few days ahead but we do look at all the reliable local forecasts and make a decent prediction twice a week.
Freak weather in Gran Canaria is anything that keeps the sunshine off the beaches for more than three days in a row. It happens about twice a year on average. Other than that, we don't get major weather events.
What about tropical storms? Only one in the last 100 years.
Earthquakes? Little ones that nobody feels.
Floods? When it rains hard, the dry valleys run with water and the odd tunnel fills up with water.
Snow? Yes, we get snow in Gran Canaria, but only right at the top of the island.
Ebola, Zika, Malaria? Nope, none of them.
Alien invasions? Tsunamis? Just go to the beach.