Great question!
The dry season of Indonesia is an annual period of little or no rainfall, and this is one of many reasons why Indonesia is so hot in the dry season.
° I can't say all the reasons, but I'll tell you a few more.
The tropics of Indonesia is dominated by the tropical rain belt, which moves from the northern to the southern tropics and back each year.
The tropical rain belt lies in the southern hemisphere very roughly from October to March - That's a whole half-year! 6 months!
↑ ↑ ↑ Hope this helps! :D
