What clothes to wear April in Fukuoka?

I'm from a tropical country and I haven't experienced any temperature lower than 20C (as written here http://www.japan-guide.com/e/e2273.html). I've been reading and some people mention that temperatures drastically fluctuate sometimes.

I'm going to Fukuoka for the entire of April and I'm not sure how thick should my outerwear be. I'm currently shopping for outerwear but several international stores with Spring wear have light jackets (blazers, cardigans, biker and denim jackets). Are these good enough or should I get something thicker?

Also, I think it's still cold in April but in popular international shops like Topshop or Zara, their clothes are so thin and very spring-like, and in tourist photos, I see people wearing thick clothes during April, so I'm really confused.

Help! :(

Shops like Zara are now selling clothes for summer, not for the current weather. It's 8 degrees in Tokyo today, so no-one is wearing a t-shirt, believe me! They might be buying them now though for use in a couple of months time.

I believe you can Google for very accurate information on average temperatures in particular areas in each month- give it a try.

Be prepared for very changeable and possibly very windy weather. Fukuoka is a bit warmer than Tokyo, but you could still find that it's 25 degrees one day, and 10 degrees the next. Take layers that are easy to take on and off. One coat should be a fairly warm one, but does not need to be down or anything that thick.