Although many people who have never been to Mexico assume it's just always warm and sunny, that's not true at all (there are many different elevations and climates within this large country), and while the seasons are less distinct, at latitude 20, I'm still quite far from the equator, so the length of days and nights do change throughout the year. In late Oct, early November, the rainy season will be over and the weather will start to cool down. Nights can be quite chilly in Jan./Feb. And it often won't rain at all, or almost never from Nov.-June.
So we are either dealing with rain, mud and a proliferation of insects in the summer or dust and dryness in the winter. Fall and spring here are less distinct, but there are many plants which only flower in the spring, just like up north, as it has to do with the number of hours of daylight, rather than the temperature.
@Lisa723 I wish I could send you some rain- we're in the middle of rainy season here and it rained so hard the other night I could hear big boulders tumbling down the rushing river which is 40 meters from my house, which woke me up at 3AM (I'm on high enough ground that I don't have to worry about getting flooded). It's actually an arroyo, as opposed to a river, so it goes dry in the winter and even after a big storm like the one the other night, when it overflows its banks, it recedes as soon as the rain stops.