good question
in the wet, or what we refer to as summer, there is a lot of water (moisture) in the air, or what we refer to as humidity
It takes a lot more of the sun's irradiation energy to increase the temperature of say, 1 cubic metre of air when it contains a lot of moisture
as we move into the dry season or our winter, the humidity drops and the air becomes dryer and so the sun's energy is able to make the air reach a higher temperature as it contains less water, this only happens to zones that are near the equator as there is still much energy generated by the sun in months like April