INDIANAPOLIS — A hot stretch starts today, with heat indices expected to top 100 degrees by mid-week. The National Weather Service warns Hoosiers about the risk of heat exhaustion and advises staying hydrated if you have to be outside.  “We’re going to get into this hot stretch over the next 4-5 days,” says Aaron Updike. “Today, the humidity should stay low enough to help reduce some heat-related hazards.”  The warmest period is between noon and 6 p.m. Updike warns that heat exhaustion can occur quickly and unexpectedly.  “Being short of breath, high heart rate, those kinds of things can be a sign of heat exhaustion,” says Updike. “So try to avoid it as best as possible by taking those breaks and staying hydrated.”  Rain and thunderstorms are expected this week, which might help with Indiana’s drought after more than a week without measurable rain. Updike says a high-pressure system is causing these conditions.  “Whenever we get those systems, it causes these massive heat stretches across the Midwest,” he added.