Welcome to my forum. Glad you found it. Generally the weather in September is pretty good. Of course no one can accurately predict it so count on rain and be grateful for sunshine. Take a look at my "Weather" page. It has a temperature chart near the bottom. Also, if you click on any weather box around the map of Ireland you can look up the weather for any month or year.
Be sure to take a spin around my website for valuable info. This page will get the ball rolling: http://www.irelandyes.com/planning.html Feel free to post any other questions you might have.