The body dissipates heat 4 ways:
Conduction – heat transfer from one solid object to another. The transfer is always from the warmer object to the cooler object.
Radiation – the loss of heat in the form of infrared rays
Convection – heat transfer from the body to the surrounding air. Air temperature must be cooler than skin temperature in order for this to occur. Wind is a good example.
Evaporation – sweat from the skin results in heat loss by the body.*
If the body isn't accustomed to warm weather exercises, it takes approximately 10-14 days of exercise in those conditions in order to fully acclimate yourself.
Your body's "temperature regulation center," called the hypothalamus, adjusts during this period. Changes during this period include sweat rate increases, sweating begins earlier, better distribution of sweat over the whole body, sweat becomes hypotonic (less salty), and blood volume increases.