Typically, you can expect that the weather in Abergavenny throughout September is 15. Average high degrees are usually 20 degrees celsius and a low of 13 celsius. We have put some more information here:
Abergavenny, UK Weather in September FAQs
Typically what weather am I expecting?
The usual weather is 15 celsius although it does change during the day
What’s the difference in weather in the summer vs. winter?
Winter to Summer average temperatures change by 6 degrees
How cold should I expect it to get?