Why is equatorial region hot and wet throughout the year

That is the reason why Equatorial regions are hot. The angle made by Sun rays is almost constant throughout the year near these regions. So the region witnesses a fairly uniform temperature throughout the year ... High temperatures evaporates the water so that's why its humid and it often results in convectional rain.

Explanation:

They are perpetually hot throughout the year as the sun rays almost hit them directly with not much changes on the solstices too.

And the water vapor saturates the air which is why it is always humid and by late afternoon, there is just too much water vapor in the air that it starts to rain - heavily. And then the evenings are pleasant, and before you know it, night falls