What information do you already have? If you want to do a day trip, do you have an idea regarding from where?
OK, there is no road to the summit. You arrange transport by road up to a point where the road ends, and the route to the summit is about 3 hours walk one way from there.
Arranging road transport is the tricky part. Taxis from Sfakia probably would not take you (road not good for their cars). A pickup truck would be required.
The easiest thing to do would be to stay at the following place in Anopoli.
They arrange transport themselves, as standard part of what they offer. Otherwise you have to ask around and find a shepard who is willing to take you up. O Platanos Rooms to Let across the square might also take you up, but may be less predictable.
I've never been there in August. Rain as such is unlikely to be an issue. However, mountains do create their own weather and depending on wind direction, the peaks might be hidden in clouds, even when it is sunny blue skies everywhere else. It is impossible to predict this. You just have to go and see what the weather is like.