Mexico climate :
The Tropic of Cancer effectively divides the country into temperate and tropical zones. Land north of the twenty-fourth parallel experiences cooler temperatures during the winter months. South of the twenty-fourth parallel, temperatures are fairly constant year round and vary solely as a function of elevation.This gives Mexico one of the worlds most diverse weather systems in the world.Areas south of the twenty-fourth parallel with elevations up to 1,000 meters (the southern parts of both coastal plains as well as the Yucatán Peninsula), have a yearly median temperature between 24 and 28 °C. Temperatures here remain high throughout the year, with only a 5 °C difference between winter and summer median temperatures. Although low-lying areas north of the twentieth-fourth parallel are hot and humid during the summer, they generally have lower yearly temperature averages (from 20 to 24 °C) because of more moderate conditions during the winter.
Many large cities in Mexico are located in the Valley of Mexico or in adjacent valleys with altitudes generally above 2,000 m, this gives them a year-round temperate climate with yearly temperature averages (from 16 to 18 °C) and cool nighttime temperatures throughout the year. Many parts of Mexico, particularly the north, have a dry climate with sporadic rainfall while parts of the tropical lowlands in the south average more than 200 cm of annual precipitation.
" The Tropic of Cancer, or Northern tropic, is one of five major circles of latitude that mark maps of the Earth. It is the northernmost latitude at which the Sun can appear directly overhead at noon. This event occurs at the June solstice, when the northern hemisphere is tilted towards the sun to its maximum extent."