I live in Okinawa not to far from Taiwan, I would think the wind patterns are kind of similar (not very strong during summer unless a Typhoon hits) however it should blow quite stronger N, NE winds though the Taiwan Straight starting October/November.
stick to the west side spots this time of year. guangyi is probably the closest to taipei but junan is better. it's about an hour south. guangyi is far too polluted which in taiwan standards means it's about 100 times worse than anywhere else in the world. we're just getting into the winter weather pattern so sept can be hit or miss. this week looks pretty good 10-12m weather pretty much all week. winter is usually 6-10m, summer 9-14m and typhoon season can be 5-7m with the usual close out.
look for "tonys spot" in junan (chunan) as he has fresh beer, some food, a bunk room for rent, and knows the general deal.