Dangers of Heat and being prepared
Most of the year, when exercising, the cold weather provides an instant cooling system. The aim is not to cool down too fast and suffer hypothermia - when the body gets dangerously too cold.
Within only a few days the goal has changed to one of avoiding overheating - hyperthermia - which can be dangerous very quickly.
Water is the key. In hot weather, your body sweats. This releases a great deal more water and salts (minerals) out of the body. If this is not replaced, the body will over heat, and with it comes poor performance, and health risk.
Water is the key, by and large. Drinking water regularly through the day before a workout, keep drinking water during, and refill your body, after a workout. This ensures optimal muscle function - including transport of oxygen and removal of lactic acid and waste minerals from the muscles - AND it allows the body to continue cooling itself with sweat. Keeping cool relies on water, and plenty of it.
Keep a drink handy. Just thought I'd mention it.