Temperatures hopped into the low 90s on Friday evening along America's midwest and east coast in the first sign of the weekend's coming heat wave. About 195 million people were under a heat watch, warning or advisory Friday morning, and the National Weather Service issued an excessive heat warning across the entirety of some states going into Saturday. Philadelphia is projected to see a heat index of 115 degrees on Saturday, while cities stretching from Boston to Oklahoma City are expected to break into the triple digits. The National Weather Service has cautioned that heat is the top cause of weather-related deaths. The heat puts this month on track for the Earth's warmest July ever recorded, coming after the hottest June on record as well.

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