From my experience of having visited Mallorca during almost every month of the year at some time, the weather can be very changeable. Yes, July and August will be hot but often in May and June you can have rain and certainly chilly evenings in May.
Then there's always the chance of a good thunderstorm. I've been told by locals that February and November are the wettest months. Mallorca is an island in the Mediterranean about halfway up the eastern coast of Spain so it will not often get the searing heat and dryness of the south of Spain.
Going late August into September should be good but you could experience showers once into September. Put it this way, I've never felt really cold anywhere in Mallorca, certainly not like in the UK!
The other thing you have to realise with PP is that it is surrounded by the Traumantana mountains so geographically because of that the weather can be changeable. For me though, the mountains are one of the many things that make PP what it is.