As travelers prepare to set off on summer trips, scorching temperatures lie in wait. Above-average temperatures could be on the books this summer, according to forecasters, and a developing El Nino event could spell out warmer weather later in the year or next summer. Sizzling temperatures are more than an inconvenience: They can cause heat exhaustion and life-threatening heat stroke. Travelers can take precautions to have fun with heat preparedness in mind. “The same way that we prepare for...