This Guardian article, Heat: the next big inequality issue, highlights the issues of 2018 and the prognosis that can be expected. Let's face it, if we lose electrical power in a heat emergency, many more people will die than we have seen perish in the past. And, it won't be just the poor and homeless.
We are getting close to a time when construction workers will not be able to work outside when we have extreme heat days. Roofers in particular and those doing asphalt paving are extremely vulnerable to heat injuries.
Even Seattle, a typically cooler city, has cooling center plans. Yesterday and today, we have had record heat temperatures for May, topping out in the mid-80s. A nice summer day in many parts of the United States, but hot by our normal standards. It was in the 60s earlier in the week.
Your disaster response plan needs to have a section on heat emergencies, those that happen when the electrical power is on, and for when the lights and air conditioning won't come on due to a power outage.