This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
Also, this is a specific month, so it uses the がつ reading.
Two years from now I will turn sixty in October.
It should gradually be getting cooler in October.
It’s my fault that he’s acting strange; I asked him to go swimming even though it is October.