Recently my prof asked a question:
Why in subequatorial regions do we have six months of rainy season and six months dry season?
How do wet and dry seasons 'form'? I can't find the answer anywhere on the net. Can anyone help with the answer?
You should read about the intertropical convergence zone and its seasonal movements. Here you will find all the answers.
The ITCZ follows the sun as the convergence happens where most of the radiation comes in. As the ITCZ has finite depth it means that some regions are only under its influence when it is at its northernmost or southernmost location, and these are the regions your professor mentioned.