Calculate apparent temperature (feels like) from air temperature and humidity.
The heat index (also called "feels like" or apparent temperature) combines air temperature with relative humidity to estimate how hot it feels to the body. High humidity slows sweat evaporation, so the same air temperature feels hotter.
Method: NWS heat index procedure (Rothfusz regression with its low and high humidity adjustments; a simpler formula when the heat index is below about 80°F / 26.7°C). Categories follow the NOAA heat index chart and are for people in higher risk groups in shady conditions; full sun can add up to 15°F (about 8°C), and strong wind in very hot, dry air can be hazardous. NWS states the regression is not valid for extreme temperature and humidity conditions beyond the range of the data it was built on, so treat results at extremes as approximate. This is a general estimate, not medical advice. Sources: NWS equation, NOAA chart.
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