April things heat up, May sees some thunderstorms due to the intense heat and in June everyone is awaiting the onset of the rains, which in the first few days causes flooding.

July-Sept is OK to travel as the rains are more regular and the initial flooding due to clogged drains et al subsides. Everything is still warm/hot and very moist. You could have phases of 2-3 hours where it rains buckets. If you plan for that you can visit the sites inbetween the rain.