The tropics are specific regions, not general hot places. Countries close to the Tropic of Cancer experience hot climates.
Pro Tip 2/3
23.5 Degrees
'Tropic' lines mark 23.5 degrees north and south of the equator. Mexico lies just inside the Tropic of Cancer.
Pro Tip 3/3
Seasonal Relevance
The position of the sun at solstices defines the tropic lines. The Tropic of Capricorn is the southern limit for the sun's vertical rays during December.